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- Committer: Package Import Robot
- Author(s): Jonathan Davies
- Date: 2014-01-20 19:00:59 UTC
- mfrom: (1.2.6)
- Revision ID: package-import@ubuntu.com-20140120190059-z8e4dl3g8cd09yi5
Tags: 5.1.2~dr3+git20130120-0ubuntu1
* Upstream Git snapshot for build fixes with regards to entropy.
* debian/rules:
- Enforcing DEB_BUILD_OPTIONS=nostrip for library integrity checking.
- Set TESTS_REDUCED_KEYLENGTHS to one generate smallest key-lengths in
tests.
* debian/rules:
- Enforcing DEB_BUILD_OPTIONS=nostrip for library integrity checking.
- Set TESTS_REDUCED_KEYLENGTHS to one generate smallest key-lengths in
tests.
- files added:
- HACKING
- doc
- doc/standards
- packages
- packages/maemo-applet
- packages/maemo-applet/debian
- packages/maemo-applet/debian/source
- packages/maemo-strongswan
- packages/maemo-strongswan/debian
- packages/maemo-strongswan/debian/patches
- packages/maemo-strongswan/debian/source
- packages/network-manager-strongswan
- packages/network-manager-strongswan/debian
- packages/strongswan
- packages/strongswan/debian
- src/dumm/patches
- src/dumm/scripts
- src/frontends
- src/frontends/android
- src/frontends/android/jni
- src/frontends/android/jni/libandroidbridge
- src/frontends/android/jni/libandroidbridge/backend
- src/frontends/android/jni/libandroidbridge/byod
- src/frontends/android/jni/libandroidbridge/kernel
- src/frontends/android/res
- src/frontends/android/res/drawable
- src/frontends/android/res/drawable-hdpi
- src/frontends/android/res/drawable-mdpi
- src/frontends/android/res/drawable-xhdpi
- src/frontends/android/res/layout
- src/frontends/android/res/layout-large
- src/frontends/android/res/menu
- src/frontends/android/res/values
- src/frontends/android/res/values-de
- src/frontends/android/res/values-pl
- src/frontends/android/res/values-ru
- src/frontends/android/res/values-ua
- src/frontends/android/src
- src/frontends/android/src/org
- src/frontends/android/src/org/strongswan
- src/frontends/android/src/org/strongswan/android
- src/frontends/android/src/org/strongswan/android/data
- src/frontends/android/src/org/strongswan/android/logic
- src/frontends/android/src/org/strongswan/android/logic/imc
- src/frontends/android/src/org/strongswan/android/logic/imc/attributes
- src/frontends/android/src/org/strongswan/android/logic/imc/collectors
- src/frontends/android/src/org/strongswan/android/ui
- src/frontends/android/src/org/strongswan/android/ui/adapter
- src/frontends/android/src/org/strongswan/android/utils
- src/frontends/gnome
- src/frontends/gnome/auth-dialog
- src/frontends/gnome/debian
- src/frontends/gnome/m4
- src/frontends/gnome/po
- src/frontends/gnome/properties
- src/frontends/maemo
- src/frontends/maemo/data
- src/frontends/maemo/data/icons
- src/frontends/maemo/data/icons/18x18
- src/frontends/maemo/data/icons/48x48
- src/frontends/maemo/src
- src/frontends/osx
- src/frontends/osx/charon-xpc
- src/frontends/osx/strongSwan.xcodeproj
- src/libpts/plugins/imc_swid/regid.1999-03.org.debian
- files removed:
- Android.common.mk
- files modified:
- NEWS
added
removed
doc/standards/rfc4186.txt
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Network Working Group H. Haverinen, Ed.
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Request for Comments: 4186 Nokia
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Category: Informational J. Salowey, Ed.
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Cisco Systems
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January 2006
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Extensible Authentication Protocol Method for
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Global System for Mobile Communications (GSM)
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Subscriber Identity Modules (EAP-SIM)
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Status of This Memo
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This memo provides information for the Internet community. It does
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not specify an Internet standard of any kind. Distribution of this
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memo is unlimited.
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Copyright Notice
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Copyright (C) The Internet Society (2006).
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IESG Note
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The EAP-SIM protocol was developed by 3GPP. The documentation of
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EAP-SIM is provided as information to the Internet community. While
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the EAP WG has verified that EAP-SIM is compatible with EAP, as
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defined in RFC 3748, no other review has been done, including
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validation of the security claims. The IETF has also not reviewed
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the security of the cryptographic algorithms.
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Abstract
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This document specifies an Extensible Authentication Protocol (EAP)
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mechanism for authentication and session key distribution using the
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Global System for Mobile Communications (GSM) Subscriber Identity
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Module (SIM). GSM is a second generation mobile network standard.
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The EAP-SIM mechanism specifies enhancements to GSM authentication
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and key agreement whereby multiple authentication triplets can be
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combined to create authentication responses and session keys of
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greater strength than the individual GSM triplets. The mechanism
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also includes network authentication, user anonymity support, result
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indications, and a fast re-authentication procedure.
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Haverinen & Salowey Informational [Page 1]
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RFC 4186 EAP-SIM Authentication January 2006
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Table of Contents
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1. Introduction ....................................................4
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2. Terms ...........................................................5
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3. Overview ........................................................8
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4. Operation ......................................................10
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4.1. Version Negotiation .......................................10
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4.2. Identity Management .......................................11
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4.2.1. Format, Generation and Usage of Peer Identities ....11
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4.2.2. Communicating the Peer Identity to the Server ......17
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4.2.3. Choice of Identity for the EAP-Response/Identity ...19
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4.2.4. Server Operation in the Beginning of
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EAP-SIM Exchange ...................................19
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4.2.5. Processing of EAP-Request/SIM/Start by the Peer ....20
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4.2.6. Attacks Against Identity Privacy ...................21
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4.2.7. Processing of AT_IDENTITY by the Server ............22
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4.3. Message Sequence Examples (Informative) ...................23
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4.3.1. Full Authentication ................................24
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4.3.2. Fast Re-authentication .............................25
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4.3.3. Fall Back to Full Authentication ...................26
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4.3.4. Requesting the Permanent Identity 1 ................27
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4.3.5. Requesting the Permanent Identity 2 ................28
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4.3.6. Three EAP-SIM/Start Roundtrips .....................28
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5. Fast Re-Authentication .........................................30
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5.1. General ...................................................30
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5.2. Comparison to UMTS AKA ....................................31
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5.3. Fast Re-authentication Identity ...........................31
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5.4. Fast Re-authentication Procedure ..........................33
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5.5. Fast Re-authentication Procedure when Counter Is
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Too Small .................................................36
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6. EAP-SIM Notifications ..........................................37
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6.1. General ...................................................37
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6.2. Result Indications ........................................39
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6.3. Error Cases ...............................................40
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6.3.1. Peer Operation .....................................40
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6.3.2. Server Operation ...................................41
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6.3.3. EAP-Failure ........................................42
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6.3.4. EAP-Success ........................................42
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7. Key Generation .................................................43
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8. Message Format and Protocol Extensibility ......................45
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8.1. Message Format ............................................45
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8.2. Protocol Extensibility ....................................47
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9. Messages .......................................................48
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9.1. EAP-Request/SIM/Start .....................................48
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9.2. EAP-Response/SIM/Start ....................................49
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9.3. EAP-Request/SIM/Challenge .................................49
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9.4. EAP-Response/SIM/Challenge ................................50
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9.5. EAP-Request/SIM/Re-authentication .........................51
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Haverinen & Salowey Informational [Page 2]
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9.6. EAP-Response/SIM/Re-authentication ........................51
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9.7. EAP-Response/SIM/Client-Error .............................52
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9.8. EAP-Request/SIM/Notification ..............................52
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9.9. EAP-Response/SIM/Notification .............................53
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10. Attributes ....................................................53
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10.1. Table of Attributes ......................................53
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10.2. AT_VERSION_LIST ..........................................54
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10.3. AT_SELECTED_VERSION ......................................55
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10.4. AT_NONCE_MT ..............................................55
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10.5. AT_PERMANENT_ID_REQ ......................................56
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10.6. AT_ANY_ID_REQ ............................................56
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10.7. AT_FULLAUTH_ID_REQ .......................................57
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10.8. AT_IDENTITY ..............................................57
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10.9. AT_RAND ..................................................58
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10.10. AT_NEXT_PSEUDONYM .......................................59
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10.11. AT_NEXT_REAUTH_ID .......................................59
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10.12. AT_IV, AT_ENCR_DATA, and AT_PADDING .....................60
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10.13. AT_RESULT_IND ...........................................62
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10.14. AT_MAC ..................................................62
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10.15. AT_COUNTER ..............................................63
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10.16. AT_COUNTER_TOO_SMALL ....................................63
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10.17. AT_NONCE_S ..............................................64
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10.18. AT_NOTIFICATION .........................................64
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10.19. AT_CLIENT_ERROR_CODE ....................................65
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11. IANA Considerations ...........................................66
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12. Security Considerations .......................................66
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12.1. A3 and A8 Algorithms .....................................66
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12.2. Identity Protection ......................................66
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12.3. Mutual Authentication and Triplet Exposure ...............67
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12.4. Flooding the Authentication Centre .......................69
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12.5. Key Derivation ...........................................69
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12.6. Cryptographic Separation of Keys and Session
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Independence .............................................70
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12.7. Dictionary Attacks .......................................71
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12.8. Credentials Re-use .......................................71
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12.9. Integrity and Replay Protection, and Confidentiality .....72
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12.10. Negotiation Attacks .....................................73
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12.11. Protected Result Indications ............................73
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12.12. Man-in-the-Middle Attacks ...............................74
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12.13. Generating Random Numbers ...............................74
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13. Security Claims ...............................................74
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14. Acknowledgements and Contributions ............................75
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14.1. Contributors .............................................75
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14.2. Acknowledgements .........................................75
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14.2.1. Contributors' Addresses ...........................77
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15. References ....................................................78
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15.1. Normative References .....................................78
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15.2. Informative References ...................................79
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Haverinen & Salowey Informational [Page 3]
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Appendix A. Test Vectors .........................................81
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A.1. EAP-Request/Identity .....................................81
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A.2. EAP-Response/Identity ....................................81
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A.3. EAP-Request/SIM/Start ....................................82
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A.4. EAP-Response/SIM/Start ...................................82
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A.5. EAP-Request/SIM/Challenge ................................83
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A.6. EAP-Response/SIM/Challenge ...............................86
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A.7. EAP-Success ..............................................86
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A.8. Fast Re-authentication ...................................86
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A.9. EAP-Request/SIM/Re-authentication ........................87
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A.10. EAP-Response/SIM/Re-authentication ......................89
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Appendix B. Pseudo-Random Number Generator .......................90
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1. Introduction
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This document specifies an Extensible Authentication Protocol (EAP)
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[RFC3748] mechanism for authentication and session key distribution
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using the Global System for Mobile Communications (GSM) Subscriber
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Identity Module (SIM).
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GSM is a second generation mobile network standard. Second
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generation mobile networks and third generation mobile networks use
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different authentication and key agreement mechanisms. EAP-AKA
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[EAP-AKA] specifies an EAP method that is based on the Authentication
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and Key Agreement (AKA) mechanism used in 3rd generation mobile
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networks.
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GSM authentication is based on a challenge-response mechanism. The
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A3/A8 authentication and key derivation algorithms that run on the
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SIM can be given a 128-bit random number (RAND) as a challenge. The
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SIM runs operator-specific algorithms, which take the RAND and a
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secret key Ki (stored on the SIM) as input, and produce a 32-bit
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response (SRES) and a 64-bit long key Kc as output. The Kc key is
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originally intended to be used as an encryption key over the air
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interface, but in this protocol, it is used for deriving keying
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material and is not directly used. Hence, the secrecy of Kc is
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critical to the security of this protocol. For more information
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about GSM authentication, see [GSM-03.20]. See Section 12.1 for more
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discussion about the GSM algorithms used in EAP-SIM.
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The lack of mutual authentication is a weakness in GSM
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authentication. The derived 64-bit cipher key (Kc) is not strong
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enough for data networks in which stronger and longer keys are
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required. Hence, in EAP-SIM, several RAND challenges are used for
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generating several 64-bit Kc keys, which are combined to constitute
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stronger keying material. In EAP-SIM, the client issues a random
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number NONCE_MT to the network in order to contribute to key
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derivation, and to prevent replays of EAP-SIM requests from previous
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Haverinen & Salowey Informational [Page 4]
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RFC 4186 EAP-SIM Authentication January 2006
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exchanges. The NONCE_MT can be conceived as the client's challenge
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to the network. EAP-SIM also extends the combined RAND challenges
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and other messages with a message authentication code in order to
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provide message integrity protection along with mutual
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authentication.
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EAP-SIM specifies optional support for protecting the privacy of
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subscriber identity using the same concept as the GSM, which uses
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pseudonyms/temporary identifiers. It also specifies an optional fast
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re-authentication procedure.
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The security of EAP-SIM builds on underlying GSM mechanisms. The
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security properties of EAP-SIM are documented in Section 11 of this
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document. Implementers and users of EAP-SIM are advised to carefully
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study the security considerations in Section 11 in order to determine
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whether the security properties are sufficient for the environment in
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question, especially as the secrecy of Kc keys is essential to the
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security of EAP-SIM. In brief, EAP-SIM is in no sense weaker than
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the GSM mechanisms. In some cases EAP-SIM provides better security
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properties than the underlying GSM mechanisms, particularly if the
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SIM credentials are only used for EAP-SIM and are not re-used from
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GSM/GPRS. Many of the security features of EAP-SIM rely upon the
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secrecy of the Kc values in the SIM triplets, so protecting these
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values is key to the security of the EAP-SIM protocol.
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The 3rd Generation Partnership Project (3GPP) has specified an
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enhanced Authentication and Key Agreement (AKA) architecture for the
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Universal Mobile Telecommunications System (UMTS). The 3rd
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generation AKA mechanism includes mutual authentication, replay
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protection, and derivation of longer session keys. EAP-AKA [EAP-AKA]
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specifies an EAP method that is based on the 3rd generation AKA.
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EAP-AKA, which is a more secure protocol, may be used instead of
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EAP-SIM, if 3rd generation identity modules and 3G network
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infrastructures are available.
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2. Terms
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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document are to be interpreted as described in [RFC2119].
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The terms and abbreviations "authenticator", "backend authentication
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server", "EAP server", "peer", "Silently Discard", "Master Session
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Key (MSK)", and "Extended Master Session Key (EMSK)" in this document
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are to be interpreted as described in [RFC3748].
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This document frequently uses the following terms and abbreviations:
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AAA protocol
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Authentication, Authorization, and Accounting protocol
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AuC
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Authentication Centre. The GSM network element that provides
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the authentication triplets for authenticating
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the subscriber.
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Authentication vector
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GSM triplets can be alternatively called authentication
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vectors.
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EAP
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Extensible Authentication Protocol
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Fast re-authentication
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An EAP-SIM authentication exchange that is based on keys
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derived upon a preceding full authentication exchange.
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The GSM authentication and key exchange algorithms are not
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used in the fast re-authentication procedure.
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Fast Re-authentication Identity
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A fast re-authentication identity of the peer, including an NAI
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realm portion in environments where a realm is used. Used on
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fast re-authentication only.
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Fast Re-authentication Username
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The username portion of fast re-authentication identity,
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i.e., not including any realm portions.
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Full authentication
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An EAP-SIM authentication exchange based on the GSM
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authentication and key agreement algorithms.
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GSM
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Global System for Mobile communications.
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GSM Triplet
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The tuple formed by the three GSM authentication values RAND,
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Kc, and SRES.
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IMSI
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International Mobile Subscriber Identifier, used in GSM to
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identify subscribers.
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MAC
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Message Authentication Code
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NAI
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Network Access Identifier
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Nonce
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A value that is used at most once or that is never repeated
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within the same cryptographic context. In general, a nonce can
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be predictable (e.g., a counter) or unpredictable (e.g., a
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random value). Since some cryptographic properties may depend
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on the randomness of the nonce, attention should be paid to
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whether a nonce is required to be random or not. In this
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document, the term nonce is only used to denote random nonces,
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and it is not used to denote counters.
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Permanent Identity
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The permanent identity of the peer, including an NAI realm
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portion in environments where a realm is used. The permanent
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identity is usually based on the IMSI. Used on full
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authentication only.
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Permanent Username
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The username portion of permanent identity, i.e., not including
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any realm portions.
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Pseudonym Identity
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A pseudonym identity of the peer, including an NAI realm
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portion in environments where a realm is used. Used on
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full authentication only.
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Pseudonym Username
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The username portion of pseudonym identity, i.e., not including
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any realm portions.
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SIM
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Subscriber Identity Module. The SIM is traditionally a smart
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card distributed by a GSM operator.
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3. Overview
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Figure 1 shows an overview of the EAP-SIM full authentication
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procedure, wherein optional protected success indications are not
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used. The authenticator typically communicates with an EAP server
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that is located on a backend authentication server using an AAA
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protocol. The authenticator shown in the figure is often simply
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relaying EAP messages to and from the EAP server, but these backend
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AAA communications are not shown.
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Peer Authenticator
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| EAP-Request/Identity |
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|<---------------------------------------------------------|
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| |
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| EAP-Response/Identity |
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|--------------------------------------------------------->|
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| |
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| EAP-Request/SIM/Start (AT_VERSION_LIST) |
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|<---------------------------------------------------------|
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| |
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| EAP-Response/SIM/Start (AT_NONCE_MT, AT_SELECTED_VERSION)|
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|--------------------------------------------------------->|
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| |
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| EAP-Request/SIM/Challenge (AT_RAND, AT_MAC) |
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|<---------------------------------------------------------|
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+-------------------------------------+ |
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| Peer runs GSM algorithms, verifies | |
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| AT_MAC and derives session keys | |
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+-------------------------------------+ |
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| EAP-Response/SIM/Challenge (AT_MAC) |
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|--------------------------------------------------------->|
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| |
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| EAP-Success |
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|<---------------------------------------------------------|
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| |
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Figure 1: EAP-SIM full authentication procedure
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RFC 4186 EAP-SIM Authentication January 2006
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The first EAP Request issued by the authenticator is
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EAP-Request/Identity. On full authentication, the peer's response
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includes either the user's International Mobile Subscriber Identity
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(IMSI) or a temporary identity (pseudonym) if identity privacy is in
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effect, as specified in Section 4.2.
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Following the peer's EAP-Response/Identity packet, the peer receives
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EAP Requests of Type 18 (SIM) from the EAP server and sends the
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corresponding EAP Responses. The EAP packets that are of the Type
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SIM also have a Subtype field. On full authentication, the first
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EAP-Request/SIM packet is of the Subtype 10 (Start). EAP-SIM packets
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encapsulate parameters in attributes, encoded in a Type, Length,
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Value format. The packet format and the use of attributes are
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specified in Section 8.
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The EAP-Request/SIM/Start packet contains the list of EAP-SIM
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versions supported by the EAP server in the AT_VERSION_LIST
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attribute. This packet may also include attributes for requesting
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the subscriber identity, as specified in Section 4.2.
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The peer responds to a EAP-Request/SIM/Start with the
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EAP-Response/SIM/Start packet, which includes the AT_NONCE_MT
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attribute that contains a random number NONCE_MT, chosen by the peer,
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and the AT_SELECTED_VERSION attribute that contains the version
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number selected by the peer. The version negotiation is protected by
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including the version list and the selected version in the
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calculation of keying material (Section 7).
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After receiving the EAP Response/SIM/Start, the EAP server obtains n
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GSM triplets for use in authenticating the subscriber, where n = 2 or
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n = 3. From the triplets, the EAP server derives the keying
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material, as specified in Section 7. The triplets may be obtained by
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contacting an Authentication Centre (AuC) on the GSM network; per GSM
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specifications, between 1 and 5 triplets may be obtained at a time.
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Triplets may be stored in the EAP server for use at a later time, but
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triplets MUST NOT be re-used, except in some error cases that are
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specified in Section 10.9.
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The next EAP Request the EAP Server issues is of the type SIM and
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subtype Challenge (11). It contains the RAND challenges and a
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message authentication code attribute AT_MAC to cover the challenges.
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The AT_MAC attribute is a general message authentication code
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attribute that is used in many EAP-SIM messages.
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On receipt of the EAP-Request/SIM/Challenge message, the peer runs
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the GSM authentication algorithm and calculates a copy of the message
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authentication code. The peer then verifies that the calculated MAC
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equals the received MAC. If the MAC's do not match, then the peer
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RFC 4186 EAP-SIM Authentication January 2006
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sends the EAP-Response/SIM/Client-Error packet and the authentication
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exchange terminates.
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Since the RANDs given to a peer are accompanied by the message
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authentication code AT_MAC, and since the peer's NONCE_MT value
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contributes to AT_MAC, the peer is able to verify that the EAP-SIM
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message is fresh (i.e., not a replay) and that the sender possesses
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valid GSM triplets for the subscriber.
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If all checks out, the peer responds with the
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EAP-Response/SIM/Challenge, containing the AT_MAC attribute that
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covers the peer's SRES response values (Section 9.4). The EAP server
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verifies that the MAC is correct. Because protected success
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indications are not used in this example, the EAP server sends the
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EAP-Success packet, indicating that the authentication was
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successful. (Protected success indications are discussed in
527
Section 6.2.) The EAP server may also include derived keying
528
material in the message it sends to the authenticator. The peer has
529
derived the same keying material, so the authenticator does not
530
forward the keying material to the peer along with EAP-Success.
531
532
EAP-SIM also includes a separate fast re-authentication procedure
533
that does not make use of the A3/A8 algorithms or the GSM
534
infrastructure. Fast re-authentication is based on keys derived on
535
full authentication. If the peer has maintained state information
536
for fast re-authentication and wants to use fast re-authentication,
537
then the peer indicates this by using a specific fast
538
re-authentication identity instead of the permanent identity or a
539
pseudonym identity. The fast re-authentication procedure is
540
described in Section 5.
541
542
4. Operation
543
544
4.1. Version Negotiation
545
546
EAP-SIM includes version negotiation so as to allow future
547
developments in the protocol. The version negotiation is performed
548
on full authentication and it uses two attributes, AT_VERSION_LIST,
549
which the server always includes in EAP-Request/SIM/Start, and
550
AT_SELECTED_VERSION, which the peer includes in
551
EAP-Response/SIM/Start on full authentication.
552
553
AT_VERSION_LIST includes the EAP-SIM versions supported by the
554
server. If AT_VERSION_LIST does not include a version that is
555
implemented by the peer and allowed in the peer's security policy,
556
then the peer MUST send the EAP-Response/SIM/Client-Error packet
557
(Section 9.7) to the server with the error code "unsupported
558
version". If a suitable version is included, then the peer includes
559
560
561
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565
566
567
the AT_SELECTED_VERSION attribute, containing the selected version in
568
the EAP-Response/SIM/Start packet. The peer MUST only indicate a
569
version that is included in the AT_VERSION_LIST. If several versions
570
are acceptable, then the peer SHOULD choose the version that occurs
571
first in the version list.
572
573
The version number list of AT_VERSION_LIST and the selected version
574
of AT_SELECTED_VERSION are included in the key derivation procedure
575
(Section 7). If an attacker modifies either one of these attributes,
576
then the peer and the server derive different keying material.
577
Because K_aut keys are different, the server and peer calculate
578
different AT_MAC values. Hence, the peer detects that AT_MAC,
579
included in EAP-Request/SIM/Challenge, is incorrect and sends the
580
EAP-Response/SIM/Client-Error packet. The authentication procedure
581
terminates.
582
583
4.2. Identity Management
584
585
4.2.1. Format, Generation and Usage of Peer Identities
586
587
4.2.1.1. General
588
589
In the beginning of EAP authentication, the Authenticator or the EAP
590
server usually issues the EAP-Request/Identity packet to the peer.
591
The peer responds with the EAP-Response/Identity, which contains the
592
user's identity. The formats of these packets are specified in
593
[RFC3748].
594
595
GSM subscribers are identified with the International Mobile
596
Subscriber Identity (IMSI) [GSM-03.03]. The IMSI is a string of not
597
more than 15 digits. It is composed of a three digit Mobile Country
598
Code (MCC), a two or three digit Mobile Network Code (MNC), and a
599
Mobile Subscriber Identification Number (MSIN) of no more than 10
600
digits. MCC and MNC uniquely identify the GSM operator and help
601
identify the AuC from which the authentication vectors need to be
602
retrieved for this subscriber.
603
604
Internet AAA protocols identify users with the Network Access
605
Identifier (NAI) [RFC4282]. When used in a roaming environment, the
606
NAI is composed of a username and a realm, separated with "@"
607
(username@realm). The username portion identifies the subscriber
608
within the realm.
609
610
This section specifies the peer identity format used in EAP-SIM. In
611
this document, the term "identity" or "peer identity" refers to the
612
whole identity string that is used to identify the peer. The peer
613
614
615
616
617
618
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621
622
623
identity may include a realm portion. "Username" refers to the
624
portion of the peer identity that identifies the user, i.e., the
625
username does not include the realm portion.
626
627
4.2.1.2. Identity Privacy Support
628
629
EAP-SIM includes optional identity privacy (anonymity) support that
630
can be used to hide the cleartext permanent identity and thereby make
631
the subscriber's EAP exchanges untraceable to eavesdroppers. Because
632
the permanent identity never changes, revealing it would help
633
observers to track the user. The permanent identity is usually based
634
on the IMSI, which may further help the tracking, because the same
635
identifier may be used in other contexts as well. Identity privacy
636
is based on temporary identities, or pseudonyms, which are equivalent
637
to but separate from the Temporary Mobile Subscriber Identities
638
(TMSI) that are used on cellular networks. Please see Section 12.2
639
for security considerations regarding identity privacy.
640
641
4.2.1.3. Username Types in EAP-SIM identities
642
643
There are three types of usernames in EAP-SIM peer identities:
644
645
(1) Permanent usernames. For example,
646
1123456789098765@myoperator.com might be a valid permanent identity.
647
In this example, 1123456789098765 is the permanent username.
648
649
(2) Pseudonym usernames. For example, 3s7ah6n9q@myoperator.com might
650
be a valid pseudonym identity. In this example, 3s7ah6n9q is the
651
pseudonym username.
652
653
(3) Fast re-authentication usernames. For example,
654
53953754@myoperator.com might be a valid fast re-authentication
655
identity. In this case, 53953754 is the fast re-authentication
656
username. Unlike permanent usernames and pseudonym usernames, fast
657
re-authentication usernames are one-time identifiers, which are not
658
re-used across EAP exchanges.
659
660
The first two types of identities are used only on full
661
authentication and the last one only on fast re-authentication. When
662
the optional identity privacy support is not used, the non-pseudonym
663
permanent identity is used on full authentication. The fast
664
re-authentication exchange is specified in Section 5.
665
666
4.2.1.4. Username Decoration
667
668
In some environments, the peer may need to decorate the identity by
669
prepending or appending the username with a string, in order to
670
indicate supplementary AAA routing information in addition to the NAI
671
672
673
674
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677
678
679
realm. (The usage of an NAI realm portion is not considered
680
decoration.) Username decoration is out of the scope of this
681
document. However, it should be noted that username decoration might
682
prevent the server from recognizing a valid username. Hence,
683
although the peer MAY use username decoration in the identities that
684
the peer includes in EAP-Response/Identity, and although the EAP
685
server MAY accept a decorated peer username in this message, the peer
686
or the EAP server MUST NOT decorate any other peer identities that
687
are used in various EAP-SIM attributes. Only the identity used in
688
the EAP-Response/Identity may be decorated.
689
690
4.2.1.5. NAI Realm Portion
691
692
The peer MAY include a realm portion in the peer identity, as per the
693
NAI format. The use of a realm portion is not mandatory.
694
695
If a realm is used, the realm MAY be chosen by the subscriber's home
696
operator and it MAY be a configurable parameter in the EAP-SIM peer
697
implementation. In this case, the peer is typically configured with
698
the NAI realm of the home operator. Operators MAY reserve a specific
699
realm name for EAP-SIM users. This convention makes it easy to
700
recognize that the NAI identifies a GSM subscriber. Such a reserved
701
NAI realm may be a useful hint as to the first authentication method
702
to use during method negotiation. When the peer is using a pseudonym
703
username instead of the permanent username, the peer selects the
704
realm name portion similarly as it select the realm portion when
705
using the permanent username.
706
707
If no configured realm name is available, the peer MAY derive the
708
realm name from the MCC and MNC portions of the IMSI. A RECOMMENDED
709
way to derive the realm from the IMSI using the realm 3gppnetwork.org
710
is specified in [3GPP-TS-23.003].
711
712
Some old implementations derive the realm name from the IMSI by
713
concatenating "mnc", the MNC digits of IMSI, ".mcc", the MCC digits
714
of IMSI, and ".owlan.org". For example, if the IMSI is
715
123456789098765, and the MNC is three digits long, then the derived
716
realm name is "mnc456.mcc123.owlan.org". As there are no DNS servers
717
running at owlan.org, these realm names can only be used with
718
manually configured AAA routing. New implementations SHOULD use the
719
mechanism specified in [3GPP-TS-23.003] instead of owlan.org.
720
721
The IMSI is a string of digits without any explicit structure, so the
722
peer may not be able to determine the length of the MNC portion. If
723
the peer is not able to determine whether the MNC is two or three
724
digits long, the peer MAY use a 3-digit MNC. If the correct length
725
of the MNC is two, then the MNC used in the realm name includes the
726
first digit of the MSIN. Hence, when configuring AAA networks for
727
728
729
730
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RFC 4186 EAP-SIM Authentication January 2006
733
734
735
operators that have 2-digit MNCs, the network SHOULD also be prepared
736
for realm names with incorrect, 3-digit MNCs.
737
738
4.2.1.6. Format of the Permanent Username
739
740
The non-pseudonym permanent username SHOULD be derived from the IMSI.
741
In this case, the permanent username MUST be of the format "1" |
742
IMSI, where the character "|" denotes concatenation. In other words,
743
the first character of the username is the digit one (ASCII value 31
744
hexadecimal), followed by the IMSI. The IMSI is encoded as an ASCII
745
string that consists of not more than 15 decimal digits (ASCII values
746
between 30 and 39 hexadecimal), one character per IMSI digit, in the
747
order specified in [GSM-03.03]. For example, a permanent username
748
derived from the IMSI 295023820005424 would be encoded as the ASCII
749
string "1295023820005424" (byte values in hexadecimal notation: 31 32
750
39 35 30 32 33 38 32 30 30 30 35 34 32 34).
751
752
The EAP server MAY use the leading "1" as a hint to try EAP-SIM as
753
the first authentication method during method negotiation, rather
754
than, for example EAP/AKA. The EAP-SIM server MAY propose EAP-SIM,
755
even if the leading character was not "1".
756
757
Alternatively, an implementation MAY choose a permanent username that
758
is not based on the IMSI. In this case, the selection of the
759
username, its format, and its processing is out of the scope of this
760
document. In this case, the peer implementation MUST NOT prepend any
761
leading characters to the username.
762
763
4.2.1.7. Generating Pseudonyms and Fast Re-authentication Identities by
764
the Server
765
766
Pseudonym usernames and fast re-authentication identities are
767
generated by the EAP server. The EAP server produces pseudonym
768
usernames and fast re-authentication identities in an
769
implementation-dependent manner. Only the EAP server needs to be
770
able to map the pseudonym username to the permanent identity, or to
771
recognize a fast re-authentication identity.
772
773
EAP-SIM includes no provisions to ensure that the same EAP server
774
that generated a pseudonym username will be used on the
775
authentication exchange when the pseudonym username is used. It is
776
recommended that the EAP servers implement some centralized mechanism
777
to allow all EAP servers of the home operator to map pseudonyms
778
generated by other severs to the permanent identity. If no such
779
mechanism is available, then the EAP server failing to understand a
780
pseudonym issued by another server can request the that peer send the
781
permanent identity.
782
783
784
785
786
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RFC 4186 EAP-SIM Authentication January 2006
789
790
791
When issuing a fast re-authentication identity, the EAP server may
792
include a realm name in the identity to make the fast
793
re-authentication request be forwarded to the same EAP server.
794
795
When generating fast re-authentication identities, the server SHOULD
796
choose a fresh, new fast re-authentication identity that is different
797
from the previous ones that were used after the same full
798
authentication exchange. A full authentication exchange and the
799
associated fast re-authentication exchanges are referred to here as
800
the same "full authentication context". The fast re-authentication
801
identity SHOULD include a random component. This random component
802
works as a full authentication context identifier. A
803
context-specific fast re-authentication identity can help the server
804
to detect whether its fast re-authentication state information
805
matches that of its peer (in other words, whether the state
806
information is from the same full authentication exchange). The
807
random component also makes the fast re-authentication identities
808
unpredictable, so an attacker cannot initiate a fast
809
re-authentication exchange to get the server's EAP-Request/SIM/
810
Re-authentication packet.
811
812
Transmitting pseudonyms and fast re-authentication identities from
813
the server to the peer is discussed in Section 4.2.1.8. The
814
pseudonym is transmitted as a username, without an NAI realm, and the
815
fast re-authentication identity is transmitted as a complete NAI,
816
including a realm portion if a realm is required. The realm is
817
included in the fast re-authentication identity to allow the server
818
to include a server-specific realm.
819
820
Regardless of the construction method, the pseudonym username MUST
821
conform to the grammar specified for the username portion of an NAI.
822
The fast re-authentication identity also MUST conform to the NAI
823
grammar. The EAP servers that the subscribers of an operator can use
824
MUST ensure that the pseudonym usernames and the username portions
825
used in fast re-authentication identities they generate are unique.
826
827
In any case, it is necessary that permanent usernames, pseudonym
828
usernames, and fast re-authentication usernames are separate and
829
recognizable from each other. It is also desirable that EAP-SIM and
830
EAP-AKA [EAP-AKA] usernames be distinguishable from each other as an
831
aid for the server on which method to offer.
832
833
In general, it is the task of the EAP server and the policies of its
834
administrator to ensure sufficient separation of the usernames.
835
Pseudonym usernames and fast re-authentication usernames are both
836
produced and used by the EAP server. The EAP server MUST compose
837
pseudonym usernames and fast re-authentication usernames so that it
838
can determine if an NAI username is an EAP-SIM pseudonym username or
839
840
841
842
Haverinen & Salowey Informational [Page 15]
843
844
RFC 4186 EAP-SIM Authentication January 2006
845
846
847
an EAP-SIM fast re-authentication username. For instance, when the
848
usernames have been derived from the IMSI, the server could use
849
different leading characters in the pseudonym usernames and fast
850
re-authentication usernames (e.g., the pseudonym could begin with a
851
leading "3" character). When mapping a fast re-authentication
852
identity to a permanent identity, the server SHOULD only examine the
853
username portion of the fast re-authentication identity and ignore
854
the realm portion of the identity.
855
856
Because the peer may fail to save a pseudonym username sent in an
857
EAP-Request/SIM/Challenge, for example due to malfunction, the EAP
858
server SHOULD maintain at least the most recently used pseudonym
859
username in addition to the most recently issued pseudonym username.
860
If the authentication exchange is not completed successfully, then
861
the server SHOULD NOT overwrite the pseudonym username that was
862
issued during the most recent successful authentication exchange.
863
864
4.2.1.8. Transmitting Pseudonyms and Fast Re-authentication Identities
865
to the Peer
866
867
The server transmits pseudonym usernames and fast re-authentication
868
identities to the peer in cipher, using the AT_ENCR_DATA attribute.
869
870
The EAP-Request/SIM/Challenge message MAY include an encrypted
871
pseudonym username and/or an encrypted fast re-authentication
872
identity in the value field of the AT_ENCR_DATA attribute. Because
873
identity privacy support and fast re-authentication are optional
874
implementations, the peer MAY ignore the AT_ENCR_DATA attribute and
875
always use the permanent identity. On fast re-authentication
876
(discussed in Section 5), the server MAY include a new, encrypted
877
fast re-authentication identity in the
878
EAP-Request/SIM/Re-authentication message.
879
880
On receipt of the EAP-Request/SIM/Challenge, the peer MAY decrypt the
881
encrypted data in AT_ENCR_DATA. If the authentication exchange is
882
successful, and the encrypted data includes a pseudonym username,
883
then the peer may use the obtained pseudonym username on the next
884
full authentication. If a fast re-authentication identity is
885
included, then the peer MAY save it together with other fast
886
re-authentication state information, as discussed in Section 5, for
887
the next fast re-authentication. If the authentication exchange does
888
not complete successfully, the peer MUST ignore the received
889
pseudonym username and the fast re-authentication identity.
890
891
If the peer does not receive a new pseudonym username in the
892
EAP-Request/SIM/Challenge message, the peer MAY use an old pseudonym
893
username instead of the permanent username on the next full
894
authentication. The username portions of fast re-authentication
895
896
897
898
Haverinen & Salowey Informational [Page 16]
899
900
RFC 4186 EAP-SIM Authentication January 2006
901
902
903
identities are one-time usernames, which the peer MUST NOT re-use.
904
When the peer uses a fast re-authentication identity in an EAP
905
exchange, the peer MUST discard the fast re-authentication identity
906
and not re-use it in another EAP authentication exchange, even if the
907
authentication exchange was not completed.
908
909
4.2.1.9. Usage of the Pseudonym by the Peer
910
911
When the optional identity privacy support is used on full
912
authentication, the peer MAY use a pseudonym username received as
913
part of a previous full authentication sequence as the username
914
portion of the NAI. The peer MUST NOT modify the pseudonym username
915
received in AT_NEXT_PSEUDONYM. However, as discussed above, the peer
916
MAY need to decorate the username in some environments by appending
917
or prepending the username with a string that indicates supplementary
918
AAA routing information.
919
920
When using a pseudonym username in an environment where a realm
921
portion is used, the peer concatenates the received pseudonym
922
username with the "@" character and an NAI realm portion. The
923
selection of the NAI realm is discussed above. The peer can select
924
the realm portion similarly, regardless of whether it uses the
925
permanent username or a pseudonym username.
926
927
4.2.1.10. Usage of the Fast Re-authentication Identity by the Peer
928
929
On fast re-authentication, the peer uses the fast re-authentication
930
identity that was received as part of the previous authentication
931
sequence. A new re-authentication identity may be delivered as part
932
of both full authentication and fast re-authentication. The peer
933
MUST NOT modify the username part of the fast re-authentication
934
identity received in AT_NEXT_REAUTH_ID, except in cases when username
935
decoration is required. Even in these cases, the "root" fast
936
re-authentication username must not be modified, but it may be
937
appended or prepended with another string.
938
939
4.2.2. Communicating the Peer Identity to the Server
940
941
4.2.2.1. General
942
943
The peer identity MAY be communicated to the server with the
944
EAP-Response/Identity message. This message MAY contain the
945
permanent identity, a pseudonym identity, or a fast re-authentication
946
identity. If the peer uses the permanent identity or a pseudonym
947
identity, which the server is able to map to the permanent identity,
948
then the authentication proceeds as discussed in the overview of
949
Section 3. If the peer uses a fast re-authentication identity, and
950
if the fast re-authentication identity matches with a valid fast
951
952
953
954
Haverinen & Salowey Informational [Page 17]
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956
RFC 4186 EAP-SIM Authentication January 2006
957
958
959
re-authentication identity maintained by the server, and if the
960
server agrees to use fast re-authentication, then a fast
961
re-authentication exchange is performed, as described in Section 5.
962
963
The peer identity can also be transmitted from the peer to the server
964
using EAP-SIM messages instead of the EAP-Response/Identity. In this
965
case, the server includes an identity-requesting attribute
966
(AT_ANY_ID_REQ, AT_FULLAUTH_ID_REQ or AT_PERMANENT_ID_REQ) in the
967
EAP-Request/SIM/Start message, and the peer includes the AT_IDENTITY
968
attribute, which contains the peer's identity, in the
969
EAP-Response/SIM/Start message. The AT_ANY_ID_REQ attribute is a
970
general identity-requesting attribute, which the server uses if it
971
does not specify which kind of an identity the peer should return in
972
AT_IDENTITY. The server uses the AT_FULLAUTH_ID_REQ attribute to
973
request either the permanent identity or a pseudonym identity. The
974
server uses the AT_PERMANENT_ID_REQ attribute to request that the
975
peer send its permanent identity.
976
977
The identity format in the AT_IDENTITY attribute is the same as in
978
the EAP-Response/Identity packet (except that identity decoration is
979
not allowed). The AT_IDENTITY attribute contains a permanent
980
identity, a pseudonym identity, or a fast re-authentication identity.
981
982
Please note that the EAP-SIM peer and the EAP-SIM server only process
983
the AT_IDENTITY attribute; entities that only pass through EAP
984
packets do not process this attribute. Hence, the authenticator and
985
other intermediate AAA elements (such as possible AAA proxy servers)
986
will continue to refer to the peer with the original identity from
987
the EAP-Response/Identity packet unless the identity authenticated in
988
the AT_IDENTITY attribute is communicated to them in another way
989
within the AAA protocol.
990
991
4.2.2.2. Relying on EAP-Response/Identity Discouraged
992
993
The EAP-Response/Identity packet is not method-specific, so in many
994
implementations it may be handled by an EAP Framework. This
995
introduces an additional layer of processing between the EAP peer and
996
EAP server. The extra layer of processing may cache identity
997
responses or add decorations to the identity. A modification of the
998
identity response will cause the EAP peer and EAP server to use
999
different identities in the key derivation, which will cause the
1000
protocol to fail.
1001
1002
For this reason, it is RECOMMENDED that the EAP peer and server use
1003
the method-specific identity attributes in EAP-SIM, and the server is
1004
strongly discouraged from relying upon the EAP-Response/Identity.
1005
1006
1007
1008
1009
1010
Haverinen & Salowey Informational [Page 18]
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1012
RFC 4186 EAP-SIM Authentication January 2006
1013
1014
1015
In particular, if the EAP server receives a decorated identity in
1016
EAP-Response/Identity, then the EAP server MUST use the
1017
identity-requesting attributes to request that the peer send an
1018
unmodified and undecorated copy of the identity in AT_IDENTITY.
1019
1020
4.2.3. Choice of Identity for the EAP-Response/Identity
1021
1022
If EAP-SIM peer is started upon receiving an EAP-Request/Identity
1023
message, then the peer MAY use an EAP-SIM identity in the EAP-
1024
Response/Identity packet. In this case, the peer performs the
1025
following steps.
1026
1027
If the peer has maintained fast re-authentication state information
1028
and wants to use fast re-authentication, then the peer transmits the
1029
fast re-authentication identity in EAP-Response/Identity.
1030
1031
Else, if the peer has a pseudonym username available, then the peer
1032
transmits the pseudonym identity in EAP-Response/Identity.
1033
1034
In other cases, the peer transmits the permanent identity in
1035
EAP-Response/Identity.
1036
1037
4.2.4. Server Operation in the Beginning of EAP-SIM Exchange
1038
1039
As discussed in Section 4.2.2.2, the server SHOULD NOT rely on an
1040
identity string received in EAP-Response/Identity. Therefore, the
1041
RECOMMENDED way to start an EAP-SIM exchange is to ignore any
1042
received identity strings. The server SHOULD begin the EAP-SIM
1043
exchange by issuing the EAP-Request/SIM/Start packet with an
1044
identity-requesting attribute to indicate that the server wants the
1045
peer to include an identity in the AT_IDENTITY attribute of the EAP-
1046
Response/SIM/Start message. Three methods to request an identity
1047
from the peer are discussed below.
1048
1049
If the server chooses not to ignore the contents of EAP-
1050
Response/Identity, then the server may have already received an EAP-
1051
SIM identity in this packet. However, if the EAP server has not
1052
received any EAP-SIM peer identity (permanent identity, pseudonym
1053
identity, or fast re-authentication identity) from the peer when
1054
sending the first EAP-SIM request, or if the EAP server has received
1055
an EAP-Response/Identity packet but the contents do not appear to be
1056
a valid permanent identity, pseudonym identity or a re-authentication
1057
identity, then the server MUST request an identity from the peer
1058
using one of the methods below.
1059
1060
The server sends the EAP-Request/SIM/Start message with the
1061
AT_PERMANENT_ID_REQ attribute to indicate that the server wants the
1062
peer to include the permanent identity in the AT_IDENTITY attribute
1063
1064
1065
1066
Haverinen & Salowey Informational [Page 19]
1067
1068
RFC 4186 EAP-SIM Authentication January 2006
1069
1070
1071
of the EAP-Response/SIM/Start message. This is done in the following
1072
cases:
1073
1074
o The server does not support fast re-authentication or identity
1075
privacy.
1076
1077
o The server decided to process a received identity, and the server
1078
recognizes the received identity as a pseudonym identity but the
1079
server is not able to map the pseudonym identity to a permanent
1080
identity.
1081
1082
The server issues the EAP-Request/SIM/Start packet with the
1083
AT_FULLAUTH_ID_REQ attribute to indicate that the server wants the
1084
peer to include a full authentication identity (pseudonym identity or
1085
permanent identity) in the AT_IDENTITY attribute of the
1086
EAP-Response/SIM/Start message. This is done in the following cases:
1087
1088
o The server does not support fast re-authentication and the server
1089
supports identity privacy.
1090
1091
o The server decided to process a received identity, and the server
1092
recognizes the received identity as a re-authentication identity
1093
but the server is not able to map the re-authentication identity
1094
to a permanent identity.
1095
1096
The server issues the EAP-Request/SIM/Start packet with the
1097
AT_ANY_ID_REQ attribute to indicate that the server wants the peer to
1098
include an identity in the AT_IDENTITY attribute of the
1099
EAP-Response/SIM/Start message, and the server does not indicate any
1100
preferred type for the identity. This is done in other cases, such
1101
as when the server ignores a received EAP-Response/Identity, the
1102
server does not have any identity, or the server does not recognize
1103
the format of a received identity.
1104
1105
4.2.5. Processing of EAP-Request/SIM/Start by the Peer
1106
1107
Upon receipt of an EAP-Request/SIM/Start message, the peer MUST
1108
perform the following steps.
1109
1110
If the EAP-Request/SIM/Start does not include an identity request
1111
attribute, then the peer responds with EAP-Response/SIM/Start without
1112
AT_IDENTITY. The peer includes the AT_SELECTED_VERSION and
1113
AT_NONCE_MT attributes, because the exchange is a full authentication
1114
exchange.
1115
1116
If the EAP-Request/SIM/Start includes AT_PERMANENT_ID_REQ, and if the
1117
peer does not have a pseudonym available, then the peer MUST respond
1118
with EAP-Response/SIM/Start and include the permanent identity in
1119
1120
1121
1122
Haverinen & Salowey Informational [Page 20]
1123
1124
RFC 4186 EAP-SIM Authentication January 2006
1125
1126
1127
AT_IDENTITY. If the peer has a pseudonym available, then the peer
1128
MAY refuse to send the permanent identity; hence, in this case the
1129
peer MUST either respond with EAP-Response/SIM/Start and include the
1130
permanent identity in AT_IDENTITY or respond with EAP-Response/SIM/
1131
Client-Error packet with the code "unable to process packet".
1132
1133
If the EAP-Request/SIM/Start includes AT_FULL_AUTH_ID_REQ, and if the
1134
peer has a pseudonym available, then the peer SHOULD respond with
1135
EAP-Response/SIM/Start and include the pseudonym identity in
1136
AT_IDENTITY. If the peer does not have a pseudonym when it receives
1137
this message, then the peer MUST respond with EAP-Response/SIM/Start
1138
and include the permanent identity in AT_IDENTITY. The Peer MUST NOT
1139
use a re-authentication identity in the AT_IDENTITY attribute.
1140
1141
If the EAP-Request/SIM/Start includes AT_ANY_ID_REQ, and if the peer
1142
has maintained fast re-authentication state information and the peer
1143
wants to use fast re-authentication, then the peer responds with
1144
EAP-Response/SIM/Start and includes the fast re-authentication
1145
identity in AT_IDENTITY. Else, if the peer has a pseudonym identity
1146
available, then the peer responds with EAP-Response/SIM/Start and
1147
includes the pseudonym identity in AT_IDENTITY. Else, the peer
1148
responds with EAP-Response/SIM/Start and includes the permanent
1149
identity in AT_IDENTITY.
1150
1151
An EAP-SIM exchange may include several EAP/SIM/Start rounds. The
1152
server may issue a second EAP-Request/SIM/Start if it was not able to
1153
recognize the identity that the peer used in the previous AT_IDENTITY
1154
attribute. At most, three EAP/SIM/Start rounds can be used, so the
1155
peer MUST NOT respond to more than three EAP-Request/SIM/Start
1156
messages within an EAP exchange. The peer MUST verify that the
1157
sequence of EAP-Request/SIM/Start packets that the peer receives
1158
comply with the sequencing rules defined in this document. That is,
1159
AT_ANY_ID_REQ can only be used in the first EAP-Request/SIM/Start; in
1160
other words, AT_ANY_ID_REQ MUST NOT be used in the second or third
1161
EAP-Request/SIM/Start. AT_FULLAUTH_ID_REQ MUST NOT be used if the
1162
previous EAP-Request/SIM/Start included AT_PERMANENT_ID_REQ. The
1163
peer operation, in cases when it receives an unexpected attribute or
1164
an unexpected message, is specified in Section 6.3.1.
1165
1166
4.2.6. Attacks Against Identity Privacy
1167
1168
The section above specifies two possible ways the peer can operate
1169
upon receipt of AT_PERMANENT_ID_REQ. This is because a received
1170
AT_PERMANENT_ID_REQ does not necessarily originate from the valid
1171
network, but an active attacker may transmit an EAP-Request/SIM/
1172
Start packet with an AT_PERMANENT_ID_REQ attribute to the peer, in an
1173
effort to find out the true identity of the user. If the peer does
1174
not want to reveal its permanent identity, then the peer sends the
1175
1176
1177
1178
Haverinen & Salowey Informational [Page 21]
1179
1180
RFC 4186 EAP-SIM Authentication January 2006
1181
1182
1183
EAP-Response/SIM/Client-Error packet with the error code "unable to
1184
process packet", and the authentication exchange terminates.
1185
1186
Basically, there are two different policies that the peer can employ
1187
with regard to AT_PERMANENT_ID_REQ. A "conservative" peer assumes
1188
that the network is able to maintain pseudonyms robustly. Therefore,
1189
if a conservative peer has a pseudonym username, the peer responds
1190
with EAP-Response/SIM/Client-Error to the EAP packet with
1191
AT_PERMANENT_ID_REQ, because the peer believes that the valid network
1192
is able to map the pseudonym identity to the peer's permanent
1193
identity. (Alternatively, the conservative peer may accept
1194
AT_PERMANENT_ID_REQ in certain circumstances, for example, if the
1195
pseudonym was received a long time ago.) The benefit of this policy
1196
is that it protects the peer against active attacks on anonymity. On
1197
the other hand, a "liberal" peer always accepts the
1198
AT_PERMANENT_ID_REQ and responds with the permanent identity. The
1199
benefit of this policy is that it works even if the valid network
1200
sometimes loses pseudonyms and is not able to map them to the
1201
permanent identity.
1202
1203
4.2.7. Processing of AT_IDENTITY by the Server
1204
1205
When the server receives an EAP-Response/SIM/Start message with the
1206
AT_IDENTITY (in response to the server's identity requesting
1207
attribute), the server MUST operate as follows.
1208
1209
If the server used AT_PERMANENT_ID_REQ, and if the AT_IDENTITY does
1210
not contain a valid permanent identity, then the server sends
1211
EAP-Request/SIM/Notification with AT_NOTIFICATION code "General
1212
failure" (16384), and the EAP exchange terminates. If the server
1213
recognizes the permanent identity and is able to continue, then the
1214
server proceeds with full authentication by sending EAP-Request/SIM/
1215
Challenge.
1216
1217
If the server used AT_FULLAUTH_ID_REQ, and if AT_IDENTITY contains a
1218
valid permanent identity or a pseudonym identity that the server can
1219
map to a valid permanent identity, then the server proceeds with full
1220
authentication by sending EAP-Request/SIM/Challenge. If AT_IDENTITY
1221
contains a pseudonym identity that the server is not able to map to a
1222
valid permanent identity, or an identity that the server is not able
1223
to recognize or classify, then the server sends EAP-Request/SIM/Start
1224
with AT_PERMANENT_ID_REQ.
1225
1226
If the server used AT_ANY_ID_REQ, and if the AT_IDENTITY contains a
1227
valid permanent identity or a pseudonym identity that the server can
1228
map to a valid permanent identity, then the server proceeds with full
1229
authentication by sending EAP-Request/SIM/Challenge.
1230
1231
1232
1233
1234
Haverinen & Salowey Informational [Page 22]
1235
1236
RFC 4186 EAP-SIM Authentication January 2006
1237
1238
1239
If the server used AT_ANY_ID_REQ, and if AT_IDENTITY contains a valid
1240
fast re-authentication identity and the server agrees on using
1241
re-authentication, then the server proceeds with fast
1242
re-authentication by sending EAP-Request/SIM/Re-authentication
1243
(Section 5).
1244
1245
If the server used AT_ANY_ID_REQ, and if the peer sent an
1246
EAP-Response/SIM/Start with only AT_IDENTITY (indicating
1247
re-authentication), but the server is not able to map the identity to
1248
a permanent identity, then the server sends EAP-Request/SIM/Start
1249
with AT_FULLAUTH_ID_REQ.
1250
1251
If the server used AT_ANY_ID_REQ, and if AT_IDENTITY contains a valid
1252
fast re-authentication identity that the server is able to map to a
1253
permanent identity, and if the server does not want to use fast
1254
re-authentication, then the server sends EAP-Request/SIM/Start
1255
without any identity requesting attributes.
1256
1257
If the server used AT_ANY_ID_REQ, and AT_IDENTITY contains an
1258
identity that the server recognizes as a pseudonym identity but the
1259
server is not able to map the pseudonym identity to a permanent
1260
identity, then the server sends EAP-Request/SIM/Start with
1261
AT_PERMANENT_ID_REQ.
1262
1263
If the server used AT_ANY_ID_REQ, and AT_IDENTITY contains an
1264
identity that the server is not able to recognize or classify, then
1265
the server sends EAP-Request/SIM/Start with AT_FULLAUTH_ID_REQ.
1266
1267
4.3. Message Sequence Examples (Informative)
1268
1269
This section contains non-normative message sequence examples to
1270
illustrate how the peer identity can be communicated to the server.
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
Haverinen & Salowey Informational [Page 23]
1291
1292
RFC 4186 EAP-SIM Authentication January 2006
1293
1294
1295
4.3.1. Full Authentication
1296
1297
This case for full authentication is illustrated below in Figure 2.
1298
In this case, AT_IDENTITY contains either the permanent identity or a
1299
pseudonym identity. The same sequence is also used in case the
1300
server uses the AT_FULLAUTH_ID_REQ in EAP-Request/SIM/Start.
1301
1302
Peer Authenticator
1303
| |
1304
| +------------------------------+
1305
| | Server does not have a |
1306
| | Subscriber identity available|
1307
| | When starting EAP-SIM |
1308
| +------------------------------+
1309
| |
1310
| EAP-Request/SIM/Start |
1311
| (AT_ANY_ID_REQ, AT_VERSION_LIST) |
1312
|<------------------------------------------------------|
1313
| |
1314
| |
1315
| EAP-Response/SIM/Start |
1316
| (AT_IDENTITY, AT_NONCE_MT, |
1317
| AT_SELECTED_VERSION) |
1318
|------------------------------------------------------>|
1319
| |
1320
1321
Figure 2: Requesting any identity, full authentication
1322
1323
If the peer uses its full authentication identity and the AT_IDENTITY
1324
attribute contains a valid permanent identity or a valid pseudonym
1325
identity that the EAP server is able to map to the permanent
1326
identity, then the full authentication sequence proceeds as usual
1327
with the EAP Server issuing the EAP-Request/SIM/Challenge message.
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
Haverinen & Salowey Informational [Page 24]
1347
1348
RFC 4186 EAP-SIM Authentication January 2006
1349
1350
1351
4.3.2. Fast Re-authentication
1352
1353
The case when the server uses the AT_ANY_ID_REQ and the peer wants to
1354
perform fast re-authentication is illustrated below in Figure 3.
1355
1356
Peer Authenticator
1357
| |
1358
| +------------------------------+
1359
| | Server does not have a |
1360
| | Subscriber identity available|
1361
| | When starting EAP-SIM |
1362
| +------------------------------+
1363
| |
1364
| EAP-Request/SIM/Start |
1365
| (AT_ANY_ID_REQ, AT_VERSION_LIST) |
1366
|<------------------------------------------------------|
1367
| |
1368
| |
1369
| EAP-Response/SIM/Start |
1370
| (AT_IDENTITY containing a fast re-auth. identity) |
1371
|------------------------------------------------------>|
1372
| |
1373
1374
Figure 3: Requesting any identity, fast re-authentication
1375
1376
On fast re-authentication, if the AT_IDENTITY attribute contains a
1377
valid fast re-authentication identity and the server agrees on using
1378
fast re-authentication, then the server proceeds with the fast
1379
re-authentication sequence and issues the EAP-Request/SIM/
1380
Re-authentication packet, as specified in Section 5.
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
Haverinen & Salowey Informational [Page 25]
1403
1404
RFC 4186 EAP-SIM Authentication January 2006
1405
1406
1407
4.3.3. Fall Back to Full Authentication
1408
1409
Figure 4 illustrates cases in which the server does not recognize the
1410
fast re-authentication identity the peer used in AT_IDENTITY, and
1411
issues a second EAP-Request/SIM/Start message.
1412
1413
Peer Authenticator
1414
| |
1415
| +------------------------------+
1416
| | Server does not have a |
1417
| | Subscriber identity available|
1418
| | When starting EAP-SIM |
1419
| +------------------------------+
1420
| |
1421
| EAP-Request/SIM/Start |
1422
| (AT_ANY_ID_REQ, AT_VERSION_LIST) |
1423
|<------------------------------------------------------|
1424
| |
1425
| |
1426
| EAP-Response/SIM/Start |
1427
| (AT_IDENTITY containing a fast re-auth. identity) |
1428
|------------------------------------------------------>|
1429
| |
1430
| +------------------------------+
1431
| | Server does not recognize |
1432
| | The fast re-auth. |
1433
| | Identity |
1434
| +------------------------------+
1435
| |
1436
| EAP-Request/SIM/Start |
1437
| (AT_FULLAUTH_ID_REQ, AT_VERSION_LIST) |
1438
|<------------------------------------------------------|
1439
| |
1440
| |
1441
| EAP-Response/SIM/Start |
1442
| (AT_IDENTITY with a full-auth. identity, AT_NONCE_MT, |
1443
| AT_SELECTED_VERSION) |
1444
|------------------------------------------------------>|
1445
| |
1446
1447
Figure 4: Fall back to full authentication
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
Haverinen & Salowey Informational [Page 26]
1459
1460
RFC 4186 EAP-SIM Authentication January 2006
1461
1462
1463
4.3.4. Requesting the Permanent Identity 1
1464
1465
Figure 5 illustrates the case in which the EAP server fails to map
1466
the pseudonym identity included in the EAP-Response/Identity packet
1467
to a valid permanent identity.
1468
1469
Peer Authenticator
1470
| |
1471
| EAP-Request/Identity |
1472
|<------------------------------------------------------|
1473
| |
1474
| EAP-Response/Identity |
1475
| (Includes a pseudonym) |
1476
|------------------------------------------------------>|
1477
| |
1478
| +------------------------------+
1479
| | Server fails to map the |
1480
| | Pseudonym to a permanent id. |
1481
| +------------------------------+
1482
| EAP-Request/SIM/Start |
1483
| (AT_PERMANENT_ID_REQ, AT_VERSION_LIST) |
1484
|<------------------------------------------------------|
1485
| |
1486
| EAP-Response/SIM/Start |
1487
| (AT_IDENTITY with permanent identity, AT_NONCE_MT, |
1488
| AT_SELECTED_VERSION) |
1489
|------------------------------------------------------>|
1490
| |
1491
1492
Figure 5: Requesting the permanent identity
1493
1494
If the server recognizes the permanent identity, then the
1495
authentication sequence proceeds as usual with the EAP Server issuing
1496
the EAP-Request/SIM/Challenge message.
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
Haverinen & Salowey Informational [Page 27]
1515
1516
RFC 4186 EAP-SIM Authentication January 2006
1517
1518
1519
4.3.5. Requesting the Permanent Identity 2
1520
1521
Figure 6 illustrates the case in which the EAP server fails to map
1522
the pseudonym included in the AT_IDENTITY attribute to a valid
1523
permanent identity.
1524
1525
Peer Authenticator
1526
| |
1527
| +------------------------------+
1528
| | Server does not have a |
1529
| | Subscriber identity available|
1530
| | When starting EAP-SIM |
1531
| +------------------------------+
1532
| EAP-Request/SIM/Start |
1533
| (AT_ANY_ID_REQ, AT_VERSION_LIST) |
1534
|<------------------------------------------------------|
1535
| |
1536
|EAP-Response/SIM/Start |
1537
|(AT_IDENTITY with a pseudonym identity, AT_NONCE_MT, |
1538
| AT_SELECTED_VERSION) |
1539
|------------------------------------------------------>|
1540
| +-------------------------------+
1541
| | Server fails to map the |
1542
| | Pseudonym in AT_IDENTITY |
1543
| | to a valid permanent identity |
1544
| +-------------------------------+
1545
| |
1546
| EAP-Request/SIM/Start |
1547
| (AT_PERMANENT_ID_REQ, AT_VERSION_LIST) |
1548
|<------------------------------------------------------|
1549
| |
1550
| EAP-Response/SIM/Start |
1551
| (AT_IDENTITY with permanent identity, |
1552
| AT_NONCE_MT, AT_SELECTED_VERSION) |
1553
|------------------------------------------------------>|
1554
| |
1555
1556
Figure 6: Requesting a permanent identity (two EAP-SIM Start rounds)
1557
1558
4.3.6. Three EAP-SIM/Start Roundtrips
1559
1560
In the worst case, there are three EAP/SIM/Start round trips before
1561
the server obtains an acceptable identity. This case is illustrated
1562
in Figure 7.
1563
1564
1565
1566
1567
1568
1569
1570
Haverinen & Salowey Informational [Page 28]
1571
1572
RFC 4186 EAP-SIM Authentication January 2006
1573
1574
1575
Peer Authenticator
1576
| |
1577
| +------------------------------+
1578
| | Server does not have a |
1579
| | Subscriber identity available|
1580
| | When starting EAP-SIM |
1581
| +------------------------------+
1582
| EAP-Request/SIM/Start |
1583
| (Includes AT_ANY_ID_REQ, AT_VERSION_LIST) |
1584
|<------------------------------------------------------|
1585
| |
1586
| EAP-Response/SIM/Start |
1587
| (AT_IDENTITY with fast re-auth. identity) |
1588
|------------------------------------------------------>|
1589
| |
1590
| +------------------------------+
1591
| | Server does not accept |
1592
| | The fast re-auth. |
1593
| | Identity |
1594
| +------------------------------+
1595
| EAP-Request/SIM/Start |
1596
| (AT_FULLAUTH_ID_REQ, AT_VERSION_LIST) |
1597
|<------------------------------------------------------|
1598
| |
1599
: :
1600
: :
1601
: :
1602
: :
1603
|EAP-Response/SIM/Start |
1604
|(AT_IDENTITY with a pseudonym identity, AT_NONCE_MT, |
1605
| AT_SELECTED_VERSION) |
1606
|------------------------------------------------------>|
1607
| |
1608
| +-------------------------------+
1609
| | Server fails to map the |
1610
| | Pseudonym in AT_IDENTITY |
1611
| | to a valid permanent identity |
1612
| +-------------------------------+
1613
| EAP-Request/SIM/Start |
1614
| (AT_PERMANENT_ID_REQ, AT_VERSION_LIST) |
1615
|<------------------------------------------------------|
1616
| |
1617
| EAP-Response/SIM/Start |
1618
| (AT_IDENTITY with permanent identity, AT_NONCE_MT, |
1619
| AT_SELECTED_VERSION) |
1620
|------------------------------------------------------>|
1621
| |
1622
Figure 7: Three EAP-SIM Start rounds
1623
1624
1625
1626
Haverinen & Salowey Informational [Page 29]
1627
1628
RFC 4186 EAP-SIM Authentication January 2006
1629
1630
1631
After the last EAP-Response/SIM/Start message, the full
1632
authentication sequence proceeds as usual. If the EAP Server
1633
recognizes the permanent identity and is able to proceed, the server
1634
issues the EAP-Request/SIM/Challenge message.
1635
1636
5. Fast Re-Authentication
1637
1638
5.1. General
1639
1640
In some environments, EAP authentication may be performed frequently.
1641
Because the EAP-SIM full authentication procedure makes use of the
1642
GSM SIM A3/A8 algorithms, and therefore requires 2 or 3 fresh
1643
triplets from the Authentication Centre, the full authentication
1644
procedure is not very well suited for frequent use. Therefore,
1645
EAP-SIM includes a more inexpensive fast re-authentication procedure
1646
that does not make use of the SIM A3/A8 algorithms and does not need
1647
new triplets from the Authentication Centre. Re-authentication can
1648
be performed in fewer roundtrips than the full authentication.
1649
1650
Fast re-authentication is optional to implement for both the EAP-SIM
1651
server and peer. On each EAP authentication, either one of the
1652
entities may also fall back on full authentication if it does not
1653
want to use fast re-authentication.
1654
1655
Fast re-authentication is based on the keys derived on the preceding
1656
full authentication. The same K_aut and K_encr keys that were used
1657
in full authentication are used to protect EAP-SIM packets and
1658
attributes, and the original Master Key from full authentication is
1659
used to generate a fresh Master Session Key, as specified in Section
1660
7.
1661
1662
The fast re-authentication exchange makes use of an unsigned 16-bit
1663
counter, included in the AT_COUNTER attribute. The counter has three
1664
goals: 1) it can be used to limit the number of successive
1665
reauthentication exchanges without full authentication 2) it
1666
contributes to the keying material, and 3) it protects the peer and
1667
the server from replays. On full authentication, both the server and
1668
the peer initialize the counter to one. The counter value of at
1669
least one is used on the first fast re-authentication. On subsequent
1670
fast re-authentications, the counter MUST be greater than on any of
1671
the previous re-authentications. For example, on the second fast
1672
re-authentication, the counter value is two or greater. The
1673
AT_COUNTER attribute is encrypted.
1674
1675
Both the peer and the EAP server maintain a copy of the counter. The
1676
EAP server sends its counter value to the peer in the fast
1677
re-authentication request. The peer MUST verify that its counter
1678
value is less than or equal to the value sent by the EAP server.
1679
1680
1681
1682
Haverinen & Salowey Informational [Page 30]
1683
1684
RFC 4186 EAP-SIM Authentication January 2006
1685
1686
1687
The server includes an encrypted server random nonce (AT_NONCE_S) in
1688
the fast re-authentication request. The AT_MAC attribute in the
1689
peer's response is calculated over NONCE_S to provide a
1690
challenge/response authentication scheme. The NONCE_S also
1691
contributes to the new Master Session Key.
1692
1693
Both the peer and the server SHOULD have an upper limit for the
1694
number of subsequent fast re-authentications allowed before a full
1695
authentication needs to be performed. Because a 16-bit counter is
1696
used in fast re-authentication, the theoretical maximum number of
1697
re-authentications is reached when the counter value reaches FFFF
1698
hexadecimal.
1699
1700
In order to use fast re-authentication, the peer and the EAP server
1701
need to store the following values: Master Key, latest counter value
1702
and the next fast re-authentication identity. K_aut, K_encr may
1703
either be stored or derived again from MK. The server may also need
1704
to store the permanent identity of the user.
1705
1706
5.2. Comparison to UMTS AKA
1707
1708
When analyzing the fast re-authentication exchange, it may be helpful
1709
to compare it with the UMTS Authentication and Key Agreement (AKA)
1710
exchange, which it resembles closely. The counter corresponds to the
1711
UMTS AKA sequence number, NONCE_S corresponds to RAND, AT_MAC in
1712
EAP-Request/SIM/Re-authentication corresponds to AUTN, the AT_MAC in
1713
EAP-Response/SIM/Re-authentication corresponds to RES,
1714
AT_COUNTER_TOO_SMALL corresponds to AUTS, and encrypting the counter
1715
corresponds to the usage of the Anonymity Key. Also, the key
1716
generation on fast re-authentication, with regard to random or fresh
1717
material, is similar to UMTS AKA -- the server generates the NONCE_S
1718
and counter values, and the peer only verifies that the counter value
1719
is fresh.
1720
1721
It should also be noted that encrypting the AT_NONCE_S, AT_COUNTER,
1722
or AT_COUNTER_TOO_SMALL attributes is not important to the security
1723
of the fast re-authentication exchange.
1724
1725
5.3. Fast Re-authentication Identity
1726
1727
The fast re-authentication procedure makes use of separate
1728
re-authentication user identities. Pseudonyms and the permanent
1729
identity are reserved for full authentication only. If a
1730
re-authentication identity is lost and the network does not recognize
1731
it, the EAP server can fall back on full authentication.
1732
1733
1734
1735
1736
1737
1738
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1739
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RFC 4186 EAP-SIM Authentication January 2006
1741
1742
1743
If the EAP server supports fast re-authentication, it MAY include the
1744
skippable AT_NEXT_REAUTH_ID attribute in the encrypted data of
1745
EAP-Request/SIM/Challenge message (Section 9.3). This attribute
1746
contains a new fast re-authentication identity for the next fast
1747
re-authentication. The attribute also works as a capability flag
1748
that, indicating that the server supports fast re-authentication, and
1749
that the server wants to continue using fast re-authentication within
1750
the current context. The peer MAY ignore this attribute, in which
1751
case it MUST use full authentication next time. If the peer wants to
1752
use re-authentication, it uses this fast re-authentication identity
1753
on next authentication. Even if the peer has a fast
1754
re-authentication identity, the peer MAY discard the fast
1755
re-authentication identity and use a pseudonym or the permanent
1756
identity instead, in which case full authentication MUST be
1757
performed. If the EAP server does not include the AT_NEXT_REAUTH_ID
1758
in the encrypted data of EAP-Request/SIM/Challenge or
1759
EAP-Request/SIM/ Re-authentication, then the peer MUST discard its
1760
current fast re-authentication state information and perform a full
1761
authentication next time.
1762
1763
In environments where a realm portion is needed in the peer identity,
1764
the fast re-authentication identity received in AT_NEXT_REAUTH_ID
1765
MUST contain both a username portion and a realm portion, as per the
1766
NAI format. The EAP Server can choose an appropriate realm part in
1767
order to have the AAA infrastructure route subsequent fast
1768
re-authentication related requests to the same AAA server. For
1769
example, the realm part MAY include a portion that is specific to the
1770
AAA server. Hence, it is sufficient to store the context required
1771
for fast re-authentication in the AAA server that performed the full
1772
authentication.
1773
1774
The peer MAY use the fast re-authentication identity in the
1775
EAP-Response/Identity packet or, in response to the server's
1776
AT_ANY_ID_REQ attribute, the peer MAY use the fast re-authentication
1777
identity in the AT_IDENTITY attribute of the EAP-Response/SIM/Start
1778
packet.
1779
1780
The peer MUST NOT modify the username portion of the fast
1781
re-authentication identity, but the peer MAY modify the realm portion
1782
or replace it with another realm portion. The peer might need to
1783
modify the realm in order to influence the AAA routing, for example,
1784
to make sure that the correct server is reached. It should be noted
1785
that sharing the same fast re-authentication key among several
1786
servers may have security risks, so changing the realm portion of the
1787
NAI in order to change the EAP server is not desirable.
1788
1789
1790
1791
1792
1793
1794
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1795
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RFC 4186 EAP-SIM Authentication January 2006
1797
1798
1799
Even if the peer uses a fast re-authentication identity, the server
1800
may want to fall back on full authentication, for example because the
1801
server does not recognize the fast re-authentication identity or does
1802
not want to use fast re-authentication. In this case, the server
1803
starts the full authentication procedure by issuing an
1804
EAP-Request/SIM/Start packet. This packet always starts a full
1805
authentication sequence if it does not include the AT_ANY_ID_REQ
1806
attribute. If the server was not able to recover the peer's identity
1807
from the fast re-authentication identity, the server includes either
1808
the AT_FULLAUTH_ID_REQ or the AT_PERMANENT_ID_REQ attribute in this
1809
EAP request.
1810
1811
5.4. Fast Re-authentication Procedure
1812
1813
Figure 8 illustrates the fast re-authentication procedure. In this
1814
example, the optional protected success indication is not used.
1815
Encrypted attributes are denoted with '*'. The peer uses its
1816
re-authentication identity in the EAP-Response/Identity packet. As
1817
discussed above, an alternative way to communicate the
1818
re-authentication identity to the server is for the peer to use the
1819
AT_IDENTITY attribute in the EAP-Response/SIM/Start message. This
1820
latter case is not illustrated in the figure below, and it is only
1821
possible when the server requests that the peer send its identity by
1822
including the AT_ANY_ID_REQ attribute in the EAP-Request/SIM/Start
1823
packet.
1824
1825
If the server recognizes the identity as a valid fast
1826
re-authentication identity, and if the server agrees to use fast
1827
re-authentication, then the server sends the EAP-Request/SIM/
1828
Re-authentication packet to the peer. This packet MUST include the
1829
encrypted AT_COUNTER attribute, with a fresh counter value, the
1830
encrypted AT_NONCE_S attribute that contains a random number chosen
1831
by the server, the AT_ENCR_DATA and the AT_IV attributes used for
1832
encryption, and the AT_MAC attribute that contains a message
1833
authentication code over the packet. The packet MAY also include an
1834
encrypted AT_NEXT_REAUTH_ID attribute that contains the next fast
1835
re-authentication identity.
1836
1837
Fast re-authentication identities are one-time identities. If the
1838
peer does not receive a new fast re-authentication identity, it MUST
1839
use either the permanent identity or a pseudonym identity on the next
1840
authentication to initiate full authentication.
1841
1842
The peer verifies that AT_MAC is correct, and that the counter value
1843
is fresh (greater than any previously used value). The peer MAY save
1844
the next fast re-authentication identity from the encrypted
1845
AT_NEXT_REAUTH_ID for next time. If all checks are successful, the
1846
peer responds with the EAP-Response/SIM/Re-authentication packet,
1847
1848
1849
1850
Haverinen & Salowey Informational [Page 33]
1851
1852
RFC 4186 EAP-SIM Authentication January 2006
1853
1854
1855
including the AT_COUNTER attribute with the same counter value and
1856
AT_MAC attribute.
1857
1858
The server verifies the AT_MAC attribute and also verifies that the
1859
counter value is the same that it used in the EAP-Request/SIM/
1860
Re-authentication packet. If these checks are successful, the
1861
re-authentication has succeeded and the server sends the EAP-Success
1862
packet to the peer.
1863
1864
If protected success indications (Section 6.2) were used, the
1865
EAP-Success packet would be preceded by an EAP-SIM notification
1866
round.
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
Haverinen & Salowey Informational [Page 34]
1907
1908
RFC 4186 EAP-SIM Authentication January 2006
1909
1910
1911
Peer Authenticator
1912
| |
1913
| EAP-Request/Identity |
1914
|<------------------------------------------------------|
1915
| |
1916
| EAP-Response/Identity |
1917
| (Includes a fast re-authentication identity) |
1918
|------------------------------------------------------>|
1919
| |
1920
| +--------------------------------+
1921
| | Server recognizes the identity |
1922
| | and agrees to use fast |
1923
| | re-authentication |
1924
| +--------------------------------+
1925
| |
1926
: :
1927
: :
1928
: :
1929
: :
1930
| EAP-Request/SIM/Re-authentication |
1931
| (AT_IV, AT_ENCR_DATA, *AT_COUNTER, |
1932
| *AT_NONCE_S, *AT_NEXT_REAUTH_ID, AT_MAC) |
1933
|<------------------------------------------------------|
1934
| |
1935
+-----------------------------------------------+ |
1936
| Peer verifies AT_MAC and the freshness of | |
1937
| the counter. Peer MAY store the new fast re- | |
1938
| authentication identity for next re-auth. | |
1939
+-----------------------------------------------+ |
1940
| |
1941
| EAP-Response/SIM/Re-authentication |
1942
| (AT_IV, AT_ENCR_DATA, *AT_COUNTER with same value, |
1943
| AT_MAC) |
1944
|------------------------------------------------------>|
1945
| +--------------------------------+
1946
| | Server verifies AT_MAC and |
1947
| | the counter |
1948
| +--------------------------------+
1949
| |
1950
| EAP-Success |
1951
|<------------------------------------------------------|
1952
| |
1953
1954
Figure 8: Fast Re-authentication
1955
1956
1957
1958
1959
1960
1961
1962
Haverinen & Salowey Informational [Page 35]
1963
1964
RFC 4186 EAP-SIM Authentication January 2006
1965
1966
1967
5.5. Fast Re-authentication Procedure when Counter Is Too Small
1968
1969
If the peer does not accept the counter value of EAP-Request/SIM/
1970
Re-authentication, it indicates the counter synchronization problem
1971
by including the encrypted AT_COUNTER_TOO_SMALL in EAP-Response/SIM/
1972
Re-authentication. The server responds with EAP-Request/SIM/Start to
1973
initiate a normal full authentication procedure. This is illustrated
1974
in Figure 9. Encrypted attributes are denoted with '*'.
1975
1976
Peer Authenticator
1977
| EAP-Request/SIM/Start |
1978
| (AT_ANY_ID_REQ, AT_VERSION_LIST) |
1979
|<------------------------------------------------------|
1980
| |
1981
| EAP-Response/SIM/Start |
1982
| (AT_IDENTITY) |
1983
| (Includes a fast re-authentication identity) |
1984
|------------------------------------------------------>|
1985
| |
1986
| EAP-Request/SIM/Re-authentication |
1987
| (AT_IV, AT_ENCR_DATA, *AT_COUNTER, |
1988
| *AT_NONCE_S, *AT_NEXT_REAUTH_ID, AT_MAC) |
1989
|<------------------------------------------------------|
1990
+-----------------------------------------------+ |
1991
| AT_MAC is valid but the counter is not fresh. | |
1992
+-----------------------------------------------+ |
1993
| |
1994
| EAP-Response/SIM/Re-authentication |
1995
| (AT_IV, AT_ENCR_DATA, *AT_COUNTER_TOO_SMALL, |
1996
| *AT_COUNTER, AT_MAC) |
1997
|------------------------------------------------------>|
1998
| +----------------------------------------------+
1999
| | Server verifies AT_MAC but detects |
2000
| | That peer has included AT_COUNTER_TOO_SMALL |
2001
| +----------------------------------------------+
2002
| |
2003
| EAP-Request/SIM/Start |
2004
| (AT_VERSION_LIST) |
2005
|<------------------------------------------------------|
2006
+---------------------------------------------------------------+
2007
| Normal full authentication follows. |
2008
+---------------------------------------------------------------+
2009
| |
2010
2011
Figure 9: Fast Re-authentication, counter is not fresh
2012
2013
2014
2015
2016
2017
2018
Haverinen & Salowey Informational [Page 36]
2019
2020
RFC 4186 EAP-SIM Authentication January 2006
2021
2022
2023
In the figure above, the first three messages are similar to the
2024
basic fast re-authentication case. When the peer detects that the
2025
counter value is not fresh, it includes the AT_COUNTER_TOO_SMALL
2026
attribute in EAP-Response/SIM/Re-authentication. This attribute
2027
doesn't contain any data, but it is a request for the server to
2028
initiate full authentication. In this case, the peer MUST ignore the
2029
contents of the server's AT_NEXT_REAUTH_ID attribute.
2030
2031
On receipt of AT_COUNTER_TOO_SMALL, the server verifies AT_MAC and
2032
verifies that AT_COUNTER contains the same counter value as in the
2033
EAP-Request/SIM/Re-authentication packet. If not, the server
2034
terminates the authentication exchange by sending the
2035
EAP-Request/SIM/Notification with AT_NOTIFICATION code "General
2036
failure" (16384). If all checks on the packet are successful, the
2037
server transmits a new EAP-Request/SIM/Start packet and the full
2038
authentication procedure is performed as usual. Since the server
2039
already knows the subscriber identity, it MUST NOT include
2040
AT_ANY_ID_REQ, AT_FULLAUTH_ID_REQ, or AT_PERMANENT_ID_REQ in the
2041
EAP-Request/SIM/Start.
2042
2043
It should be noted that in this case, peer identity is only
2044
transmitted in the AT_IDENTITY attribute at the beginning of the
2045
whole EAP exchange. The fast re-authentication identity used in this
2046
AT_IDENTITY attribute will be used in key derivation (see Section 7).
2047
2048
6. EAP-SIM Notifications
2049
2050
6.1. General
2051
2052
EAP-SIM does not prohibit the use of the EAP Notifications as
2053
specified in [RFC3748]. EAP Notifications can be used at any time in
2054
the EAP-SIM exchange. It should be noted that EAP-SIM does not
2055
protect EAP Notifications. EAP-SIM also specifies method-specific
2056
EAP-SIM notifications that are protected in some cases.
2057
2058
The EAP server can use EAP-SIM notifications to convey notifications
2059
and result indications (Section 6.2) to the peer.
2060
2061
The server MUST use notifications in cases discussed in
2062
Section 6.3.2. When the EAP server issues an
2063
EAP-Request/SIM/Notification packet to the peer, the peer MUST
2064
process the notification packet. The peer MAY show a notification
2065
message to the user and the peer MUST respond to the EAP server with
2066
an EAP-Response/SIM/Notification packet, even if the peer did not
2067
recognize the notification code.
2068
2069
2070
2071
2072
2073
2074
Haverinen & Salowey Informational [Page 37]
2075
2076
RFC 4186 EAP-SIM Authentication January 2006
2077
2078
2079
An EAP-SIM full authentication exchange or a fast re-authentication
2080
exchange MUST NOT include more than one EAP-SIM notification round.
2081
2082
The notification code is a 16-bit number. The most significant bit
2083
is called the Success bit (S bit). The S bit specifies whether the
2084
notification implies failure. The code values with the S bit set to
2085
zero (code values 0...32767) are used on unsuccessful cases. The
2086
receipt of a notification code from this range implies a failed EAP
2087
exchange, so the peer can use the notification as a failure
2088
indication. After receiving the EAP-Response/SIM/Notification for
2089
these notification codes, the server MUST send the EAP-Failure
2090
packet.
2091
2092
The receipt of a notification code with the S bit set to one (values
2093
32768...65536) does not imply failure. Notification code "Success"
2094
(32768) has been reserved as a general notification code to indicate
2095
successful authentication.
2096
2097
The second most significant bit of the notification code is called
2098
the Phase bit (P bit). It specifies at which phase of the EAP-SIM
2099
exchange the notification can be used. If the P bit is set to zero,
2100
the notification can only be used after a successful
2101
EAP/SIM/Challenge round in full authentication or a successful
2102
EAP/SIM/Re-authentication round in reauthentication. A
2103
re-authentication round is considered successful only if the peer has
2104
successfully verified AT_MAC and AT_COUNTER attributes, and does not
2105
include the AT_COUNTER_TOO_SMALL attribute in
2106
EAP-Response/SIM/Re-authentication.
2107
2108
If the P bit is set to one, the notification can only by used before
2109
the EAP/SIM/Challenge round in full authentication, or before the
2110
EAP/SIM/Re-authentication round in reauthentication. These
2111
notifications can only be used to indicate various failure cases. In
2112
other words, if the P bit is set to one, then the S bit MUST be set
2113
to zero.
2114
2115
Section 9.8 and Section 9.9 specify what other attributes must be
2116
included in the notification packets.
2117
2118
Some of the notification codes are authorization related and, hence,
2119
are not usually considered part of the responsibility of an EAP
2120
method. However, they are included as part of EAP-SIM because there
2121
are currently no other ways to convey this information to the user in
2122
a localizable way, and the information is potentially useful for the
2123
user. An EAP-SIM server implementation may decide never to send
2124
these EAP-SIM notifications.
2125
2126
2127
2128
2129
2130
Haverinen & Salowey Informational [Page 38]
2131
2132
RFC 4186 EAP-SIM Authentication January 2006
2133
2134
2135
6.2. Result Indications
2136
2137
As discussed in Section 6.3, the server and the peer use explicit
2138
error messages in all error cases. If the server detects an error
2139
after successful authentication, the server uses an EAP-SIM
2140
notification to indicate failure to the peer. In this case, the
2141
result indication is integrity and replay protected.
2142
2143
By sending an EAP-Response/SIM/Challenge packet or an
2144
EAP-Response/SIM/Re-authentication packet (without
2145
AT_COUNTER_TOO_SMALL), the peer indicates that it has successfully
2146
authenticated the server and that the peer's local policy accepts the
2147
EAP exchange. In other words, these packets are implicit success
2148
indications from the peer to the server.
2149
2150
EAP-SIM also supports optional protected success indications from the
2151
server to the peer. If the EAP server wants to use protected success
2152
indications, it includes the AT_RESULT_IND attribute in the
2153
EAP-Request/SIM/Challenge or the EAP-Request/SIM/Re-authentication
2154
packet. This attribute indicates that the EAP server would like to
2155
use result indications in both successful and unsuccessful cases. If
2156
the peer also wants this, the peer includes AT_RESULT_IND in
2157
EAP-Response/SIM/Challenge or EAP-Response/SIM/Re-authentication.
2158
The peer MUST NOT include AT_RESULT_IND if it did not receive
2159
AT_RESULT_IND from the server. If both the peer and the server used
2160
AT_RESULT_IND, then the EAP exchange is not complete yet, but an
2161
EAP-SIM notification round will follow. The following EAP-SIM
2162
notification may indicate either failure or success.
2163
2164
Success indications with the AT_NOTIFICATION code "Success" (32768)
2165
can only be used if both the server and the peer indicate they want
2166
to use them with AT_RESULT_IND. If the server did not include
2167
AT_RESULT_IND in the EAP-Request/SIM/Challenge or
2168
EAP-Request/SIM/Re-authentication packet, or if the peer did not
2169
include AT_RESULT_IND in the corresponding response packet, then the
2170
server MUST NOT use protected success indications.
2171
2172
Because the server uses the AT_NOTIFICATION code "Success" (32768) to
2173
indicate that the EAP exchange has completed successfully, the EAP
2174
exchange cannot fail when the server processes the EAP-SIM response
2175
to this notification. Hence, the server MUST ignore the contents of
2176
the EAP-SIM response it receives from the
2177
EAP-Request/SIM/Notification with this code. Regardless of the
2178
contents of the EAP-SIM response, the server MUST send EAP-Success as
2179
the next packet.
2180
2181
2182
2183
2184
2185
2186
Haverinen & Salowey Informational [Page 39]
2187
2188
RFC 4186 EAP-SIM Authentication January 2006
2189
2190
2191
6.3. Error Cases
2192
2193
This section specifies the operation of the peer and the server in
2194
error cases. The subsections below require the EAP-SIM peer and
2195
server to send an error packet (EAP-Response/SIM/Client-Error from
2196
the peer or EAP-Request/SIM/Notification from the server) in error
2197
cases. However, implementations SHOULD NOT rely upon the correct
2198
error reporting behavior of the peer, authenticator, or the server.
2199
It is possible for error and other messages to be lost in transit or
2200
for a malicious participant to attempt to consume resources by not
2201
issuing error messages. Both the peer and the EAP server SHOULD have
2202
a mechanism to clean up state, even if an error message or
2203
EAP-Success is not received after a timeout period.
2204
2205
6.3.1. Peer Operation
2206
2207
In general, if an EAP-SIM peer detects an error in a received EAP-SIM
2208
packet, the EAP-SIM implementation responds with the
2209
EAP-Response/SIM/Client-Error packet. In response to the
2210
EAP-Response/SIM/Client-Error, the EAP server MUST issue the
2211
EAP-Failure packet and the authentication exchange terminates.
2212
2213
By default, the peer uses the client error code 0, "unable to process
2214
packet". This error code is used in the following cases:
2215
2216
o EAP exchange is not acceptable according to the peer's local
2217
policy.
2218
2219
o the peer is not able to parse the EAP request, i.e., the EAP
2220
request is malformed.
2221
2222
o the peer encountered a malformed attribute.
2223
2224
o wrong attribute types or duplicate attributes have been included
2225
in the EAP request.
2226
2227
o a mandatory attribute is missing.
2228
2229
o unrecognized, non-skippable attribute.
2230
2231
o unrecognized or unexpected EAP-SIM Subtype in the EAP request.
2232
2233
o A RAND challenge repeated in AT_RAND.
2234
2235
o invalid AT_MAC. The peer SHOULD log this event.
2236
2237
o invalid pad bytes in AT_PADDING.
2238
2239
2240
2241
2242
Haverinen & Salowey Informational [Page 40]
2243
2244
RFC 4186 EAP-SIM Authentication January 2006
2245
2246
2247
o the peer does not want to process AT_PERMANENT_ID_REQ.
2248
2249
Separate error codes have been defined for the following error cases
2250
in Section 10.19:
2251
2252
As specified in Section 4.1, when processing the AT_VERSION_LIST
2253
attribute, which lists the EAP-SIM versions supported by the server,
2254
if the attribute does not include a version that is implemented by
2255
the peer and allowed in the peer's security policy, then the peer
2256
MUST send the EAP-Response/SIM/Client-Error packet with the error
2257
code "unsupported version".
2258
2259
If the number of RAND challenges is smaller than what is required by
2260
peer's local policy when processing the AT_RAND attribute, the peer
2261
MUST send the EAP-Response/SIM/Client-Error packet with the error
2262
code "insufficient number of challenges".
2263
2264
If the peer believes that the RAND challenges included in AT_RAND are
2265
not fresh e.g., because it is capable of remembering some previously
2266
used RANDs, the peer MUST send the EAP-Response/SIM/Client-Error
2267
packet with the error code "RANDs are not fresh".
2268
2269
6.3.2. Server Operation
2270
2271
If an EAP-SIM server detects an error in a received EAP-SIM response,
2272
the server MUST issue the EAP-Request/SIM/Notification packet with an
2273
AT_NOTIFICATION code that implies failure. By default, the server
2274
uses one of the general failure codes ("General failure after
2275
authentication" (0), or "General failure" (16384)). The choice
2276
between these two codes depends on the phase of the EAP-SIM exchange,
2277
see Section 6. When the server issues an EAP-
2278
Request/SIM/Notification that implies failure, the error cases
2279
include the following:
2280
2281
o the server is not able to parse the peer's EAP response
2282
2283
o the server encounters a malformed attribute, a non-recognized
2284
non-skippable attribute, or a duplicate attribute
2285
2286
o a mandatory attribute is missing or an invalid attribute was
2287
included
2288
2289
o unrecognized or unexpected EAP-SIM Subtype in the EAP Response
2290
2291
o invalid AT_MAC. The server SHOULD log this event.
2292
2293
o invalid AT_COUNTER
2294
2295
2296
2297
2298
Haverinen & Salowey Informational [Page 41]
2299
2300
RFC 4186 EAP-SIM Authentication January 2006
2301
2302
2303
6.3.3. EAP-Failure
2304
2305
The EAP-SIM server sends EAP-Failure in two cases:
2306
2307
1) In response to an EAP-Response/SIM/Client-Error packet the server
2308
has received from the peer, or
2309
2310
2) Following an EAP-SIM notification round, when the AT_NOTIFICATION
2311
code implies failure.
2312
2313
The EAP-SIM server MUST NOT send EAP-Failure in cases other than
2314
these two. However, it should be noted that even though the EAP-SIM
2315
server would not send an EAP-Failure, an authorization decision that
2316
happens outside EAP-SIM, such as in the AAA server or in an
2317
intermediate AAA proxy, may result in a failed exchange.
2318
2319
The peer MUST accept the EAP-Failure packet in case 1) and case 2),
2320
above. The peer SHOULD silently discard the EAP-Failure packet in
2321
other cases.
2322
2323
6.3.4. EAP-Success
2324
2325
On full authentication, the server can only send EAP-Success after
2326
the EAP/SIM/Challenge round. The peer MUST silently discard any
2327
EAP-Success packets if they are received before the peer has
2328
successfully authenticated the server and sent the
2329
EAP-Response/SIM/Challenge packet.
2330
2331
If the peer did not indicate that it wants to use protected success
2332
indications with AT_RESULT_IND (as discussed in Section 6.2) on full
2333
authentication, then the peer MUST accept EAP-Success after a
2334
successful EAP/SIM/Challenge round.
2335
2336
If the peer indicated that it wants to use protected success
2337
indications with AT_RESULT_IND (as discussed in Section 6.2), then
2338
the peer MUST NOT accept EAP-Success after a successful
2339
EAP/SIM/Challenge round. In this case, the peer MUST only accept
2340
EAP-Success after receiving an EAP-SIM Notification with the
2341
AT_NOTIFICATION code "Success" (32768).
2342
2343
On fast re-authentication, EAP-Success can only be sent after the
2344
EAP/SIM/Re-authentication round. The peer MUST silently discard any
2345
EAP-Success packets if they are received before the peer has
2346
successfully authenticated the server and sent the
2347
EAP-Response/SIM/Re-authentication packet.
2348
2349
If the peer did not indicate that it wants to use protected success
2350
indications with AT_RESULT_IND (as discussed in Section 6.2) on fast
2351
2352
2353
2354
Haverinen & Salowey Informational [Page 42]
2355
2356
RFC 4186 EAP-SIM Authentication January 2006
2357
2358
2359
re-authentication, then the peer MUST accept EAP-Success after a
2360
successful EAP/SIM/Re-authentication round.
2361
2362
If the peer indicated that it wants to use protected success
2363
indications with AT_RESULT_IND (as discussed in Section 6.2), then
2364
the peer MUST NOT accept EAP-Success after a successful EAP/SIM/Re-
2365
authentication round. In this case, the peer MUST only accept
2366
EAP-Success after receiving an EAP-SIM Notification with the
2367
AT_NOTIFICATION code "Success" (32768).
2368
2369
If the peer receives an EAP-SIM notification (Section 6) that
2370
indicates failure, then the peer MUST no longer accept the
2371
EAP-Success packet, even if the server authentication was
2372
successfully completed.
2373
2374
7. Key Generation
2375
2376
This section specifies how keying material is generated.
2377
2378
On EAP-SIM full authentication, a Master Key (MK) is derived from the
2379
underlying GSM authentication values (Kc keys), the NONCE_MT, and
2380
other relevant context as follows.
2381
2382
MK = SHA1(Identity|n*Kc| NONCE_MT| Version List| Selected Version)
2383
2384
In the formula above, the "|" character denotes concatenation.
2385
"Identity" denotes the peer identity string without any terminating
2386
null characters. It is the identity from the last AT_IDENTITY
2387
attribute sent by the peer in this exchange, or, if AT_IDENTITY was
2388
not used, it is the identity from the EAP-Response/Identity packet.
2389
The identity string is included as-is, without any changes. As
2390
discussed in Section 4.2.2.2, relying on EAP-Response/Identity for
2391
conveying the EAP-SIM peer identity is discouraged, and the server
2392
SHOULD use the EAP-SIM method-specific identity attributes.
2393
2394
The notation n*Kc in the formula above denotes the n Kc values
2395
concatenated. The Kc keys are used in the same order as the RAND
2396
challenges in AT_RAND attribute. NONCE_MT denotes the NONCE_MT value
2397
(not the AT_NONCE_MT attribute, but only the nonce value). The
2398
Version List includes the 2-byte-supported version numbers from
2399
AT_VERSION_LIST, in the same order as in the attribute. The Selected
2400
Version is the 2-byte selected version from AT_SELECTED_VERSION.
2401
Network byte order is used, just as in the attributes. The hash
2402
function SHA-1 is specified in [SHA-1]. If several EAP/SIM/Start
2403
roundtrips are used in an EAP-SIM exchange, then the NONCE_MT,
2404
Version List and Selected version from the last EAP/SIM/Start round
2405
are used, and the previous EAP/SIM/Start rounds are ignored.
2406
2407
2408
2409
2410
Haverinen & Salowey Informational [Page 43]
2411
2412
RFC 4186 EAP-SIM Authentication January 2006
2413
2414
2415
The Master Key is fed into a Pseudo-Random number Function (PRF)
2416
which generates separate Transient EAP Keys (TEKs) for protecting
2417
EAP-SIM packets, as well as a Master Session Key (MSK) for link layer
2418
security, and an Extended Master Session Key (EMSK) for other
2419
purposes. On fast re-authentication, the same TEKs MUST be used for
2420
protecting EAP packets, but a new MSK and a new EMSK MUST be derived
2421
from the original MK and from new values exchanged in the fast
2422
re-authentication.
2423
2424
EAP-SIM requires two TEKs for its own purposes; the authentication
2425
key K_aut is to be used with the AT_MAC attribute, and the encryption
2426
key K_encr is to be used with the AT_ENCR_DATA attribute. The same
2427
K_aut and K_encr keys are used in full authentication and subsequent
2428
fast re-authentications.
2429
2430
Key derivation is based on the random number generation specified in
2431
NIST Federal Information Processing Standards (FIPS) Publication
2432
186-2 [PRF]. The pseudo-random number generator is specified in the
2433
change notice 1 (2001 October 5) of [PRF] (Algorithm 1). As
2434
specified in the change notice (page 74), when Algorithm 1 is used as
2435
a general-purpose pseudo-random number generator, the "mod q" term in
2436
step 3.3 is omitted. The function G used in the algorithm is
2437
constructed via the Secure Hash Standard, as specified in Appendix
2438
3.3 of the standard. It should be noted that the function G is very
2439
similar to SHA-1, but the message padding is different. Please refer
2440
to [PRF] for full details. For convenience, the random number
2441
algorithm with the correct modification is cited in Appendix B.
2442
2443
160-bit XKEY and XVAL values are used, so b = 160. On each full
2444
authentication, the Master Key is used as the initial secret seed-key
2445
XKEY. The optional user input values (XSEED_j) in step 3.1 are set
2446
to zero.
2447
2448
On full authentication, the resulting 320-bit random numbers (x_0,
2449
x_1, ..., x_m-1) are concatenated and partitioned into suitable-sized
2450
chunks and used as keys in the following order: K_encr (128 bits),
2451
K_aut (128 bits), Master Session Key (64 bytes), Extended Master
2452
Session Key (64 bytes).
2453
2454
On fast re-authentication, the same pseudo-random number generator
2455
can be used to generate a new Master Session Key and a new Extended
2456
Master Session Key. The seed value XKEY' is calculated as follows:
2457
2458
XKEY' = SHA1(Identity|counter|NONCE_S| MK)
2459
2460
In the formula above, the Identity denotes the fast re-authentication
2461
identity, without any terminating null characters, from the
2462
AT_IDENTITY attribute of the EAP-Response/SIM/Start packet, or, if
2463
2464
2465
2466
Haverinen & Salowey Informational [Page 44]
2467
2468
RFC 4186 EAP-SIM Authentication January 2006
2469
2470
2471
EAP-Response/SIM/Start was not used on fast re-authentication, it
2472
denotes the identity string from the EAP-Response/Identity packet.
2473
The counter denotes the counter value from the AT_COUNTER attribute
2474
used in the EAP-Response/SIM/Re-authentication packet. The counter
2475
is used in network byte order. NONCE_S denotes the 16-byte NONCE_S
2476
value from the AT_NONCE_S attribute used in the
2477
EAP-Request/SIM/Re-authentication packet. The MK is the Master Key
2478
derived on the preceding full authentication.
2479
2480
On fast re-authentication, the pseudo-random number generator is run
2481
with the new seed value XKEY', and the resulting 320-bit random
2482
numbers (x_0, x_1, ..., x_m-1) are concatenated and partitioned into
2483
two 64-byte chunks and used as the new 64-byte Master Session Key and
2484
the new 64-byte Extended Master Session Key. Note that because
2485
K_encr and K_aut are not derived on fast re-authentication, the
2486
Master Session Key and the Extended Master Session key are obtained
2487
from the beginning of the key stream (x_0, x_1, ...).
2488
2489
The first 32 bytes of the MSK can be used as the Pairwise Master Key
2490
(PMK) for IEEE 802.11i.
2491
2492
When the RADIUS attributes specified in [RFC2548] are used to
2493
transport keying material, then the first 32 bytes of the MSK
2494
correspond to MS-MPPE-RECV-KEY and the second 32 bytes to
2495
MS-MPPE-SEND-KEY. In this case, only 64 bytes of keying material
2496
(the MSK) are used.
2497
2498
When generating the initial Master Key, the hash function is used as
2499
a mixing function to combine several session keys (Kc's) generated by
2500
the GSM authentication procedure and the random number NONCE_MT into
2501
a single session key. There are several reasons for this. The
2502
current GSM session keys are, at most, 64 bits, so two or more of
2503
them are needed to generate a longer key. By using a one-way
2504
function to combine the keys, we are assured that, even if an
2505
attacker managed to learn one of the EAP-SIM session keys, it
2506
wouldn't help him in learning the original GSM Kc's. In addition,
2507
since we include the random number NONCE_MT in the calculation, the
2508
peer is able to verify that the EAP-SIM packets it receives from the
2509
network are fresh and not replays (also see Section 11).
2510
2511
8. Message Format and Protocol Extensibility
2512
2513
8.1. Message Format
2514
2515
As specified in [RFC3748], EAP packets begin with the Code,
2516
Identifiers, Length, and Type fields, which are followed by EAP-
2517
method-specific Type-Data. The Code field in the EAP header is set
2518
to 1 for EAP requests, and to 2 for EAP Responses. The usage of the
2519
2520
2521
2522
Haverinen & Salowey Informational [Page 45]
2523
2524
RFC 4186 EAP-SIM Authentication January 2006
2525
2526
2527
Length and Identifier fields in the EAP header are also specified in
2528
[RFC3748]. In EAP-SIM, the Type field is set to 18.
2529
2530
In EAP-SIM, the Type-Data begins with an EAP-SIM header that consists
2531
of a 1-octet Subtype field and a 2-octet reserved field. The Subtype
2532
values used in EAP-SIM are defined in the IANA considerations section
2533
of the EAP-AKA specification [EAP-AKA]. The formats of the EAP
2534
header and the EAP-SIM header are shown below.
2535
2536
0 1 2 3
2537
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
2538
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2539
| Code | Identifier | Length |
2540
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2541
| Type | Subtype | Reserved |
2542
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2543
2544
The rest of the Type-Data that immediately follows the EAP-SIM header
2545
consists of attributes that are encoded in Type, Length, Value
2546
format. The figure below shows the generic format of an attribute.
2547
2548
0 1 2 3
2549
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
2550
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2551
| Type | Length | Value...
2552
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2553
2554
2555
Attribute Type
2556
2557
Indicates the particular type of attribute. The attribute type
2558
values are listed in the IANA considerations section of the
2559
EAP-AKA specification [EAP-AKA].
2560
2561
Length
2562
2563
Indicates the length of this attribute in multiples of four
2564
bytes. The maximum length of an attribute is 1024 bytes. The
2565
length includes the Attribute Type and Length bytes.
2566
2567
Value
2568
2569
The particular data associated with this attribute. This field
2570
is always included and it may be two or more bytes in length.
2571
The type and length fields determine the format and length
2572
of the value field.
2573
2574
2575
2576
2577
2578
Haverinen & Salowey Informational [Page 46]
2579
2580
RFC 4186 EAP-SIM Authentication January 2006
2581
2582
2583
Attributes numbered within the range 0 through 127 are called
2584
non-skippable attributes. When an EAP-SIM peer encounters a
2585
non-skippable attribute that the peer does not recognize, the peer
2586
MUST send the EAP-Response/SIM/Client-Error packet, which terminates
2587
the authentication exchange. If an EAP-SIM server encounters a
2588
non-skippable attribute that the server does not recognize, then the
2589
server sends the EAP-Request/SIM/Notification packet with an
2590
AT_NOTIFICATION code, which implies general failure ("General failure
2591
after authentication" (0), or "General failure" (16384), depending on
2592
the phase of the exchange), which terminates the authentication
2593
exchange.
2594
2595
Attributes within the range of 128 through 255 are called skippable
2596
attributes. When a skippable attribute is encountered and is not
2597
recognized, it is ignored. The rest of the attributes and message
2598
data MUST still be processed. The Length field of the attribute is
2599
used to skip the attribute value in searching for the next attribute.
2600
2601
Unless otherwise specified, the order of the attributes in an EAP-SIM
2602
message is insignificant and an EAP-SIM implementation should not
2603
assume a certain order to be used.
2604
2605
Attributes can be encapsulated within other attributes. In other
2606
words, the value field of an attribute type can be specified to
2607
contain other attributes.
2608
2609
8.2. Protocol Extensibility
2610
2611
EAP-SIM can be extended by specifying new attribute types. If
2612
skippable attributes are used, it is possible to extend the protocol
2613
without breaking old implementations.
2614
2615
However, any new attributes added to the EAP-Request/SIM/Start or
2616
EAP-Response/SIM/Start packets would not be integrity-protected.
2617
Therefore, these messages MUST NOT be extended in the current version
2618
of EAP-SIM. If the list of supported EAP-SIM versions in the
2619
AT_VERSION_LIST does not include versions other than 1, then the
2620
server MUST NOT include attributes other than those specified in this
2621
document in the EAP-Request/SIM/Start message. Note that future
2622
versions of this protocol might specify new attributes for
2623
EAP-Request/SIM/Start and still support version 1 of the protocol.
2624
In this case, the server might send an EAP-Request/SIM/Start message
2625
that includes new attributes and indicates support for protocol
2626
version 1 and other versions in the AT_VERSION_LIST attribute. If
2627
the peer selects version 1, then the peer MUST ignore any other
2628
attributes included in EAP-Request/SIM/Start, other than those
2629
specified in this document. If the selected EAP-SIM version in
2630
peer's AT_SELECTED_VERSION is 1, then the peer MUST NOT include other
2631
2632
2633
2634
Haverinen & Salowey Informational [Page 47]
2635
2636
RFC 4186 EAP-SIM Authentication January 2006
2637
2638
2639
attributes aside from those specified in this document in the
2640
EAP-Response/SIM/Start message.
2641
2642
When specifying new attributes, it should be noted that EAP-SIM does
2643
not support message fragmentation. Hence, the sizes of the new
2644
extensions MUST be limited so that the maximum transfer unit (MTU) of
2645
the underlying lower layer is not exceeded. According to [RFC3748],
2646
lower layers must provide an EAP MTU of 1020 bytes or greater, so any
2647
extensions to EAP-SIM SHOULD NOT exceed the EAP MTU of 1020 bytes.
2648
2649
Because EAP-SIM supports version negotiation, new versions of the
2650
protocol can also be specified by using a new version number.
2651
2652
9. Messages
2653
2654
This section specifies the messages used in EAP-SIM. It specifies
2655
when a message may be transmitted or accepted, which attributes are
2656
allowed in a message, which attributes are required in a message, and
2657
other message-specific details. The general message format is
2658
specified in Section 8.1.
2659
2660
9.1. EAP-Request/SIM/Start
2661
2662
In full authentication the first SIM-specific EAP Request is
2663
EAP-Request/SIM/Start. The EAP/SIM/Start roundtrip is used for two
2664
purposes. In full authentication this packet is used to request the
2665
peer to send the AT_NONCE_MT attribute to the server. In addition,
2666
as specified in Section 4.2, the Start round trip may be used by the
2667
server for obtaining the peer identity. As discussed in Section 4.2,
2668
several Start rounds may be required to obtain a valid peer identity.
2669
2670
The server MUST always include the AT_VERSION_LIST attribute.
2671
2672
The server MAY include one of the following identity-requesting
2673
attributes: AT_PERMANENT_ID_REQ, AT_FULLAUTH_ID_REQ, or
2674
AT_ANY_ID_REQ. These three attributes are mutually exclusive, so the
2675
server MUST NOT include more than one of the attributes.
2676
2677
If the server has received a response from the peer, it MUST NOT
2678
issue a new EAP-Request/SIM/Start packet if it has previously issued
2679
an EAP-Request/SIM/Start message either without any identity
2680
requesting attributes or with the AT_PERMANENT_ID_REQ attribute.
2681
2682
If the server has received a response from the peer, it MUST NOT
2683
issue a new EAP-Request/SIM/Start packet with the AT_ANY_ID_REQ or
2684
AT_FULLAUTH_ID_REQ attributes if it has previously issued an
2685
EAP-Request/SIM/Start message with the AT_FULLAUTH_ID_REQ attribute.
2686
2687
2688
2689
2690
Haverinen & Salowey Informational [Page 48]
2691
2692
RFC 4186 EAP-SIM Authentication January 2006
2693
2694
2695
If the server has received a response from the peer, it MUST NOT
2696
issue a new EAP-Request/SIM/Start packet with the AT_ANY_ID_REQ
2697
attribute if the server has previously issued an
2698
EAP-Request/SIM/Start message with the AT_ANY_ID_REQ attribute.
2699
2700
This message MUST NOT include AT_MAC, AT_IV, or AT_ENCR_DATA.
2701
2702
9.2. EAP-Response/SIM/Start
2703
2704
The peer sends EAP-Response/SIM/Start in response to a valid
2705
EAP-Request/SIM/Start from the server.
2706
2707
If and only if the server's EAP-Request/SIM/Start includes one of the
2708
identity-requesting attributes, then the peer MUST include the
2709
AT_IDENTITY attribute. The usage of AT_IDENTITY is defined in
2710
Section 4.2.
2711
2712
The AT_NONCE_MT attribute MUST NOT be included if the AT_IDENTITY
2713
with a fast re-authentication identity is present for fast
2714
re-authentication. AT_NONCE_MT MUST be included in all other cases
2715
(full authentication).
2716
2717
The AT_SELECTED_VERSION attribute MUST NOT be included if the
2718
AT_IDENTITY attribute with a fast re-authentication identity is
2719
present for fast re-authentication. In all other cases,
2720
AT_SELECTED_VERSION MUST be included (full authentication). This
2721
attribute is used in version negotiation, as specified in
2722
Section 4.1.
2723
2724
This message MUST NOT include AT_MAC, AT_IV, or AT_ENCR_DATA.
2725
2726
9.3. EAP-Request/SIM/Challenge
2727
2728
The server sends the EAP-Request/SIM/Challenge after receiving a
2729
valid EAP-Response/SIM/Start that contains AT_NONCE_MT and
2730
AT_SELECTED_VERSION, and after successfully obtaining the subscriber
2731
identity.
2732
2733
The AT_RAND attribute MUST be included.
2734
2735
The AT_RESULT_IND attribute MAY be included. The usage of this
2736
attribute is discussed in Section 6.2.
2737
2738
The AT_MAC attribute MUST be included. For
2739
EAP-Request/SIM/Challenge, the MAC code is calculated over the
2740
following data:
2741
2742
EAP packet| NONCE_MT
2743
2744
2745
2746
Haverinen & Salowey Informational [Page 49]
2747
2748
RFC 4186 EAP-SIM Authentication January 2006
2749
2750
2751
The EAP packet is represented as specified in Section 8.1. It is
2752
followed by the 16-byte NONCE_MT value from the peer's AT_NONCE_MT
2753
attribute.
2754
2755
The EAP-Request/SIM/Challenge packet MAY include encrypted attributes
2756
for identity privacy and for communicating the next fast
2757
re-authentication identity. In this case, the AT_IV and AT_ENCR_DATA
2758
attributes are included (Section 10.12).
2759
2760
The plaintext of the AT_ENCR_DATA value field consists of nested
2761
attributes. The nested attributes MAY include AT_PADDING (as
2762
specified in Section 10.12). If the server supports identity privacy
2763
and wants to communicate a pseudonym to the peer for the next full
2764
authentication, then the nested encrypted attributes include the
2765
AT_NEXT_PSEUDONYM attribute. If the server supports
2766
re-authentication and wants to communicate a fast re-authentication
2767
identity to the peer, then the nested encrypted attributes include
2768
the AT_NEXT_REAUTH_ID attribute.
2769
2770
When processing this message, the peer MUST process AT_RAND before
2771
processing other attributes. Only if AT_RAND is verified to be
2772
valid, the peer derives keys and verifies AT_MAC. The operation in
2773
case an error occurs is specified in Section 6.3.1.
2774
2775
9.4. EAP-Response/SIM/Challenge
2776
2777
The peer sends EAP-Response/SIM/Challenge in response to a valid
2778
EAP-Request/SIM/Challenge.
2779
2780
Sending this packet indicates that the peer has successfully
2781
authenticated the server and that the EAP exchange will be accepted
2782
by the peer's local policy. Hence, if these conditions are not met,
2783
then the peer MUST NOT send EAP-Response/SIM/Challenge, but the peer
2784
MUST send EAP-Response/SIM/Client-Error.
2785
2786
The AT_MAC attribute MUST be included. For EAP-
2787
Response/SIM/Challenge, the MAC code is calculated over the following
2788
data:
2789
2790
EAP packet| n*SRES
2791
2792
The EAP packet is represented as specified in Section 8.1. The EAP
2793
packet bytes are immediately followed by the two or three SRES values
2794
concatenated, denoted above with the notation n*SRES. The SRES
2795
values are used in the same order as the corresponding RAND
2796
challenges in the server's AT_RAND attribute.
2797
2798
2799
2800
2801
2802
Haverinen & Salowey Informational [Page 50]
2803
2804
RFC 4186 EAP-SIM Authentication January 2006
2805
2806
2807
The AT_RESULT_IND attribute MAY be included if it was included in
2808
EAP-Request/SIM/Challenge. The usage of this attribute is discussed
2809
in Section 6.2.
2810
2811
Later versions of this protocol MAY make use of the AT_ENCR_DATA and
2812
AT_IV attributes in this message to include encrypted (skippable)
2813
attributes. The EAP server MUST process EAP-Response/SIM/Challenge
2814
messages that include these attributes even if the server did not
2815
implement these optional attributes.
2816
2817
9.5. EAP-Request/SIM/Re-authentication
2818
2819
The server sends the EAP-Request/SIM/Re-authentication message if it
2820
wants to use fast re-authentication, and if it has received a valid
2821
fast re-authentication identity in EAP-Response/Identity or
2822
EAP-Response/SIM/Start.
2823
2824
AT_MAC MUST be included. No message-specific data is included in the
2825
MAC calculation. See Section 10.14.
2826
2827
The AT_RESULT_IND attribute MAY be included. The usage of this
2828
attribute is discussed in Section 6.2.
2829
2830
The AT_IV and AT_ENCR_DATA attributes MUST be included. The
2831
plaintext consists of the following nested encrypted attributes,
2832
which MUST be included: AT_COUNTER and AT_NONCE_S. In addition, the
2833
nested encrypted attributes MAY include the following attributes:
2834
AT_NEXT_REAUTH_ID and AT_PADDING.
2835
2836
9.6. EAP-Response/SIM/Re-authentication
2837
2838
The client sends the EAP-Response/SIM/Re-authentication packet in
2839
response to a valid EAP-Request/SIM/Re-authentication.
2840
2841
The AT_MAC attribute MUST be included. For
2842
EAP-Response/SIM/Re-authentication, the MAC code is calculated over
2843
the following data:
2844
2845
EAP packet| NONCE_S
2846
2847
The EAP packet is represented as specified in Section 8.1. It is
2848
followed by the 16-byte NONCE_S value from the server's AT_NONCE_S
2849
attribute.
2850
2851
The AT_IV and AT_ENCR_DATA attributes MUST be included. The nested
2852
encrypted attributes MUST include the AT_COUNTER attribute. The
2853
AT_COUNTER_TOO_SMALL attribute MAY be included in the nested
2854
2855
2856
2857
2858
Haverinen & Salowey Informational [Page 51]
2859
2860
RFC 4186 EAP-SIM Authentication January 2006
2861
2862
2863
encrypted attributes, and it is included in cases specified in
2864
Section 5. The AT_PADDING attribute MAY be included.
2865
2866
The AT_RESULT_IND attribute MAY be included if it was included in
2867
EAP-Request/SIM/Re-authentication. The usage of this attribute is
2868
discussed in Section 6.2.
2869
2870
Sending this packet without AT_COUNTER_TOO_SMALL indicates that the
2871
peer has successfully authenticated the server and that the EAP
2872
exchange will be accepted by the peer's local policy. Hence, if
2873
these conditions are not met, then the peer MUST NOT send
2874
EAP-Response/SIM/Re-authentication, but the peer MUST send
2875
EAP-Response/SIM/Client-Error.
2876
2877
9.7. EAP-Response/SIM/Client-Error
2878
2879
The peer sends EAP-Response/SIM/Client-Error in error cases, as
2880
specified in Section 6.3.1.
2881
2882
The AT_CLIENT_ERROR_CODE attribute MUST be included.
2883
2884
The AT_MAC, AT_IV, or AT_ENCR_DATA attributes MUST NOT be used with
2885
this packet.
2886
2887
9.8. EAP-Request/SIM/Notification
2888
2889
The usage of this message is specified in Section 6. The
2890
AT_NOTIFICATION attribute MUST be included.
2891
2892
The AT_MAC attribute MUST be included if the P bit of the
2893
notification code in AT_NOTIFICATION is set to zero, and MUST NOT be
2894
included in cases when the P bit is set to one. The P bit is
2895
discussed in Section 6.
2896
2897
No message-specific data is included in the MAC calculation. See
2898
Section 10.14.
2899
2900
If EAP-Request/SIM/Notification is used on a fast re-authentication
2901
exchange, and if the P bit in AT_NOTIFICATION is set to zero, then
2902
AT_COUNTER is used for replay protection. In this case, the
2903
AT_ENCR_DATA and AT_IV attributes MUST be included, and the
2904
encapsulated plaintext attributes MUST include the AT_COUNTER
2905
attribute. The counter value included in AT_COUNTER MUST be the same
2906
as in the EAP-Request/SIM/Re-authentication packet on the same fast
2907
re-authentication exchange.
2908
2909
2910
2911
2912
2913
2914
Haverinen & Salowey Informational [Page 52]
2915
2916
RFC 4186 EAP-SIM Authentication January 2006
2917
2918
2919
9.9. EAP-Response/SIM/Notification
2920
2921
The usage of this message is specified in Section 6. This packet is
2922
an acknowledgement of EAP-Request/SIM/Notification.
2923
2924
The AT_MAC attribute MUST be included in cases when the P bit of the
2925
notification code in AT_NOTIFICATION of EAP-Request/SIM/Notification
2926
is set to zero, and MUST NOT be included in cases when the P bit is
2927
set to one. The P bit is discussed in Section 6.
2928
2929
No message-specific data is included in the MAC calculation, see
2930
Section 10.14.
2931
2932
If EAP-Request/SIM/Notification is used on a fast re-authentication
2933
exchange, and if the P bit in AT_NOTIFICATION is set to zero, then
2934
AT_COUNTER is used for replay protection. In this case, the
2935
AT_ENCR_DATA and AT_IV attributes MUST be included, and the
2936
encapsulated plaintext attributes MUST include the AT_COUNTER
2937
attribute. The counter value included in AT_COUNTER MUST be the same
2938
as in the EAP-Request/SIM/Re-authentication packet on the same fast
2939
re-authentication exchange.
2940
2941
10. Attributes
2942
2943
This section specifies the format of message attributes. The
2944
attribute type numbers are specified in the IANA considerations
2945
section of the EAP-AKA specification [EAP-AKA].
2946
2947
10.1. Table of Attributes
2948
2949
The following table provides a guide to which attributes may be found
2950
in which kinds of messages, and in what quantity. Messages are
2951
denoted with numbers in parentheses as follows: (1)
2952
EAP-Request/SIM/Start, (2) EAP-Response/SIM/Start, (3)
2953
EAP-Request/SIM/Challenge, (4) EAP-Response/SIM/Challenge, (5)
2954
EAP-Request/SIM/Notification, (6) EAP-Response/SIM/Notification, (7)
2955
EAP-Response/SIM/Client-Error, (8) EAP-Request/SIM/Re-authentication,
2956
and (9) EAP-Response/SIM/Re-authentication. The column denoted with
2957
"Encr" indicates whether the attribute is a nested attribute that
2958
MUST be included within AT_ENCR_DATA, and the column denoted with
2959
"Skip" indicates whether the attribute is a skippable attribute.
2960
2961
"0" indicates that the attribute MUST NOT be included in the message,
2962
"1" indicates that the attribute MUST be included in the message,
2963
"0-1" indicates that the attribute is sometimes included in the
2964
message, and "0*" indicates that the attribute is not included in the
2965
message in cases specified in this document, but MAY be included in
2966
future versions of the protocol.
2967
2968
2969
2970
Haverinen & Salowey Informational [Page 53]
2971
2972
RFC 4186 EAP-SIM Authentication January 2006
2973
2974
2975
Attribute (1) (2) (3) (4) (5) (6) (7) (8) (9) Encr Skip
2976
AT_VERSION_LIST 1 0 0 0 0 0 0 0 0 N N
2977
AT_SELECTED_VERSION 0 0-1 0 0 0 0 0 0 0 N N
2978
AT_NONCE_MT 0 0-1 0 0 0 0 0 0 0 N N
2979
AT_PERMANENT_ID_REQ 0-1 0 0 0 0 0 0 0 0 N N
2980
AT_ANY_ID_REQ 0-1 0 0 0 0 0 0 0 0 N N
2981
AT_FULLAUTH_ID_REQ 0-1 0 0 0 0 0 0 0 0 N N
2982
AT_IDENTITY 0 0-1 0 0 0 0 0 0 0 N N
2983
AT_RAND 0 0 1 0 0 0 0 0 0 N N
2984
AT_NEXT_PSEUDONYM 0 0 0-1 0 0 0 0 0 0 Y Y
2985
AT_NEXT_REAUTH_ID 0 0 0-1 0 0 0 0 0-1 0 Y Y
2986
AT_IV 0 0 0-1 0* 0-1 0-1 0 1 1 N Y
2987
AT_ENCR_DATA 0 0 0-1 0* 0-1 0-1 0 1 1 N Y
2988
AT_PADDING 0 0 0-1 0* 0-1 0-1 0 0-1 0-1 Y N
2989
AT_RESULT_IND 0 0 0-1 0-1 0 0 0 0-1 0-1 N Y
2990
AT_MAC 0 0 1 1 0-1 0-1 0 1 1 N N
2991
AT_COUNTER 0 0 0 0 0-1 0-1 0 1 1 Y N
2992
AT_COUNTER_TOO_SMALL 0 0 0 0 0 0 0 0 0-1 Y N
2993
AT_NONCE_S 0 0 0 0 0 0 0 1 0 Y N
2994
AT_NOTIFICATION 0 0 0 0 1 0 0 0 0 N N
2995
AT_CLIENT_ERROR_CODE 0 0 0 0 0 0 1 0 0 N N
2996
2997
It should be noted that attributes AT_PERMANENT_ID_REQ,
2998
AT_ANY_ID_REQ, and AT_FULLAUTH_ID_REQ are mutually exclusive; only
2999
one of them can be included at the same time. If one of the
3000
attributes AT_IV and AT_ENCR_DATA is included, then both of the
3001
attributes MUST be included.
3002
3003
10.2. AT_VERSION_LIST
3004
3005
The format of the AT_VERSION_LIST attribute is shown below.
3006
3007
0 1 2 3
3008
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
3009
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3010
| AT_VERSION_L..| Length | Actual Version List Length |
3011
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3012
| Supported Version 1 | Supported Version 2 |
3013
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3014
. .
3015
. .
3016
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3017
| Supported Version N | Padding |
3018
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3019
3020
This attribute is used in version negotiation, as specified in
3021
Section 4.1. The attribute contains the version numbers supported by
3022
the EAP-SIM server. The server MUST only include versions that it
3023
3024
3025
3026
Haverinen & Salowey Informational [Page 54]
3027
3028
RFC 4186 EAP-SIM Authentication January 2006
3029
3030
3031
implements and that are allowed in its security policy. The server
3032
SHOULD list the versions in the order of preference, with the most
3033
preferred versions listed first. At least one version number MUST be
3034
included. The version number for the protocol described in this
3035
document is one (0001 hexadecimal).
3036
3037
The value field of this attribute begins with 2-byte Actual Version
3038
List Length, which specifies the length of the Version List in bytes,
3039
not including the Actual Version List Length attribute length. This
3040
field is followed by the list of the versions supported by the
3041
server, which each have a length of 2 bytes. For example, if there
3042
is only one supported version, then the Actual Version List Length is
3043
2. Because the length of the attribute must be a multiple of 4
3044
bytes, the sender pads the value field with zero bytes when
3045
necessary.
3046
3047
10.3. AT_SELECTED_VERSION
3048
3049
The format of the AT_SELECTED_VERSION attribute is shown below.
3050
3051
0 1 2 3
3052
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
3053
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3054
| AT_SELECTED...| Length = 1 | Selected Version |
3055
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3056
3057
This attribute is used in version negotiation, as specified in
3058
Section 4.1. The value field of this attribute contains a two-byte
3059
version number, which indicates the EAP-SIM version that the peer
3060
wants to use.
3061
3062
10.4. AT_NONCE_MT
3063
3064
The format of the AT_NONCE_MT attribute is shown below.
3065
3066
0 1 2 3
3067
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
3068
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3069
|AT_NONCE_MT | Length = 5 | Reserved |
3070
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3071
| |
3072
| NONCE_MT |
3073
| |
3074
| |
3075
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3076
3077
3078
3079
3080
3081
3082
Haverinen & Salowey Informational [Page 55]
3083
3084
RFC 4186 EAP-SIM Authentication January 2006
3085
3086
3087
The value field of the NONCE_MT attribute contains two reserved bytes
3088
followed by a random number freshly generated by the peer (16 bytes
3089
long) for this EAP-SIM authentication exchange. The random number is
3090
used as a seed value for the new keying material. The reserved bytes
3091
are set to zero upon sending and ignored upon reception.
3092
3093
The peer MUST NOT re-use the NONCE_MT value from a previous EAP-SIM
3094
authentication exchange. If an EAP-SIM exchange includes several
3095
EAP/SIM/Start rounds, then the peer SHOULD use the same NONCE_MT
3096
value in all EAP-Response/SIM/Start packets. The peer SHOULD use a
3097
good source of randomness to generate NONCE_MT. Please see [RFC4086]
3098
for more information about generating random numbers for security
3099
applications.
3100
3101
10.5. AT_PERMANENT_ID_REQ
3102
3103
The format of the AT_PERMANENT_ID_REQ attribute is shown below.
3104
3105
0 1 2 3
3106
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
3107
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3108
|AT_PERM..._REQ | Length = 1 | Reserved |
3109
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3110
3111
The use of the AT_PERMANENT_ID_REQ is defined in Section 4.2. The
3112
value field contains only two reserved bytes, which are set to zero
3113
on sending and ignored on reception.
3114
3115
10.6. AT_ANY_ID_REQ
3116
3117
The format of the AT_ANY_ID_REQ attribute is shown below.
3118
3119
0 1 2 3
3120
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
3121
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3122
|AT_ANY_ID_REQ | Length = 1 | Reserved |
3123
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3124
3125
The use of the AT_ANY_ID_REQ is defined in Section 4.2. The value
3126
field contains only two reserved bytes, which are set to zero on
3127
sending and ignored on reception.
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
Haverinen & Salowey Informational [Page 56]
3139
3140
RFC 4186 EAP-SIM Authentication January 2006
3141
3142
3143
10.7. AT_FULLAUTH_ID_REQ
3144
3145
The format of the AT_FULLAUTH_ID_REQ attribute is shown below.
3146
3147
0 1 2 3
3148
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
3149
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3150
|AT_FULLAUTH_...| Length = 1 | Reserved |
3151
+---------------+---------------+-------------------------------+
3152
3153
The use of the AT_FULLAUTH_ID_REQ is defined in Section 4.2. The
3154
value field contains only two reserved bytes, which are set to zero
3155
on sending and ignored on reception.
3156
3157
10.8. AT_IDENTITY
3158
3159
The format of the AT_IDENTITY attribute is shown below.
3160
3161
0 1 2 3
3162
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
3163
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3164
| AT_IDENTITY | Length | Actual Identity Length |
3165
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3166
| |
3167
. Identity (optional) .
3168
. .
3169
| |
3170
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3171
3172
The use of the AT_IDENTITY is defined in Section 4.2. The value
3173
field of this attribute begins with a 2-byte actual identity length,
3174
which specifies the length of the identity in bytes. This field is
3175
followed by the subscriber identity of the indicated actual length.
3176
The identity is the permanent identity, a pseudonym identity, or a
3177
fast re-authentication identity. The identity format is specified in
3178
Section 4.2.1. The same identity format is used in the AT_IDENTITY
3179
attribute and the EAP-Response/Identity packet, with the exception
3180
that the peer MUST NOT decorate the identity it includes in
3181
AT_IDENTITY. The identity does not include any terminating null
3182
characters. Because the length of the attribute must be a multiple
3183
of 4 bytes, the sender pads the identity with zero bytes when
3184
necessary.
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
Haverinen & Salowey Informational [Page 57]
3195
3196
RFC 4186 EAP-SIM Authentication January 2006
3197
3198
3199
10.9. AT_RAND
3200
3201
The format of the AT_RAND attribute is shown below.
3202
3203
0 1 2 3
3204
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
3205
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3206
| AT_RAND | Length | Reserved |
3207
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3208
| |
3209
. n*RAND .
3210
. .
3211
| |
3212
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3213
3214
The value field of this attribute contains two reserved bytes
3215
followed by n GSM RANDs, each 16 bytes long. The value of n can be
3216
determined by the attribute length. The reserved bytes are set to
3217
zero upon sending and ignored upon reception.
3218
3219
The number of RAND challenges (n) MUST be two or three. The peer
3220
MUST verify that the number of RAND challenges is sufficient
3221
according to the peer's policy. The server MUST use different RAND
3222
values. In other words, a RAND value can only be included once in
3223
AT_RAND. When processing the AT_RAND attribute, the peer MUST check
3224
that the RANDs are different.
3225
3226
The EAP server MUST obtain fresh RANDs for each EAP-SIM full
3227
authentication exchange. More specifically, the server MUST consider
3228
RANDs it included in AT_RAND to be consumed if the server receives an
3229
EAP-Response/SIM/Challenge packet with a valid AT_MAC, or an
3230
EAP-Response/SIM/Client-Error with the code "insufficient number of
3231
challenges" or "RANDs are not fresh". However, in other cases (if
3232
the server does not receive a response to its
3233
EAP-Request/SIM/Challenge packet, or if the server receives a
3234
response other than the cases listed above), the server does not need
3235
to consider the RANDs to be consumed, and the server MAY re-use the
3236
RANDs in the AT_RAND attribute of the next full authentication
3237
attempt.
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
Haverinen & Salowey Informational [Page 58]
3251
3252
RFC 4186 EAP-SIM Authentication January 2006
3253
3254
3255
10.10. AT_NEXT_PSEUDONYM
3256
3257
The format of the AT_NEXT_PSEUDONYM attribute is shown below.
3258
3259
0 1 2 3
3260
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
3261
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3262
| AT_NEXT_PSEU..| Length | Actual Pseudonym Length |
3263
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3264
| |
3265
. Next Pseudonym .
3266
. .
3267
| |
3268
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3269
3270
The value field of this attribute begins with the 2-byte actual
3271
pseudonym length, which specifies the length of the following
3272
pseudonym in bytes. This field is followed by a pseudonym username
3273
that the peer can use in the next authentication. The username MUST
3274
NOT include any realm portion. The username does not include any
3275
terminating null characters. Because the length of the attribute
3276
must be a multiple of 4 bytes, the sender pads the pseudonym with
3277
zero bytes when necessary. The username encoding MUST follow the
3278
UTF-8 transformation format [RFC3629]. This attribute MUST always be
3279
encrypted by encapsulating it within the AT_ENCR_DATA attribute.
3280
3281
10.11. AT_NEXT_REAUTH_ID
3282
3283
The format of the AT_NEXT_REAUTH_ID attribute is shown below.
3284
3285
0 1 2 3
3286
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
3287
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3288
| AT_NEXT_REAU..| Length | Actual Re-Auth Identity Length|
3289
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3290
| |
3291
. Next Fast Re-authentication Username .
3292
. .
3293
| |
3294
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3295
3296
The value field of this attribute begins with the 2-byte actual
3297
re-authentication identity length which specifies the length of the
3298
following fast re-authentication identity in bytes. This field is
3299
followed by a fast re-authentication identity that the peer can use
3300
in the next fast re-authentication, as described in Section 5. In
3301
environments where a realm portion is required, the fast
3302
re-authentication identity includes both a username portion and a
3303
3304
3305
3306
Haverinen & Salowey Informational [Page 59]
3307
3308
RFC 4186 EAP-SIM Authentication January 2006
3309
3310
3311
realm name portion. The fast re-authentication identity does not
3312
include any terminating null characters. Because the length of the
3313
attribute must be a multiple of 4 bytes, the sender pads the fast
3314
re-authentication identity with zero bytes when necessary. The
3315
identity encoding MUST follow the UTF-8 transformation format
3316
[RFC3629]. This attribute MUST always be encrypted by encapsulating
3317
it within the AT_ENCR_DATA attribute.
3318
3319
10.12. AT_IV, AT_ENCR_DATA, and AT_PADDING
3320
3321
AT_IV and AT_ENCR_DATA attributes can be used to transmit encrypted
3322
information between the EAP-SIM peer and server.
3323
3324
The value field of AT_IV contains two reserved bytes followed by a
3325
16-byte initialization vector required by the AT_ENCR_DATA attribute.
3326
The reserved bytes are set to zero when sending and ignored on
3327
reception. The AT_IV attribute MUST be included if and only if the
3328
AT_ENCR_DATA is included. Section 6.3 specifies the operation if a
3329
packet that does not meet this condition is encountered.
3330
3331
The sender of the AT_IV attribute chooses the initialization vector
3332
at random. The sender MUST NOT re-use the initialization vector
3333
value from previous EAP-SIM packets. The sender SHOULD use a good
3334
source of randomness to generate the initialization vector. Please
3335
see [RFC4086] for more information about generating random numbers
3336
for security applications. The format of AT_IV is shown below.
3337
3338
0 1 2 3
3339
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
3340
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3341
| AT_IV | Length = 5 | Reserved |
3342
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3343
| |
3344
| Initialization Vector |
3345
| |
3346
| |
3347
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3348
3349
The value field of the AT_ENCR_DATA attribute consists of two
3350
reserved bytes followed by cipher text bytes encrypted using the
3351
Advanced Encryption Standard (AES) [AES] with a 128-bit key in the
3352
Cipher Block Chaining (CBC) mode of operation using the
3353
initialization vector from the AT_IV attribute. The reserved bytes
3354
are set to zero when sending and ignored on reception. Please see
3355
[CBC] for a description of the CBC mode. The format of the
3356
AT_ENCR_DATA attribute is shown below.
3357
3358
3359
3360
3361
3362
Haverinen & Salowey Informational [Page 60]
3363
3364
RFC 4186 EAP-SIM Authentication January 2006
3365
3366
3367
0 1 2 3
3368
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
3369
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3370
| AT_ENCR_DATA | Length | Reserved |
3371
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3372
| |
3373
. Encrypted Data .
3374
. .
3375
| |
3376
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3377
3378
The derivation of the encryption key (K_encr) is specified in Section
3379
7.
3380
3381
The plaintext consists of nested EAP-SIM attributes.
3382
3383
The encryption algorithm requires the length of the plaintext to be a
3384
multiple of 16 bytes. The sender may need to include the AT_PADDING
3385
attribute as the last attribute within AT_ENCR_DATA. The AT_PADDING
3386
attribute is not included if the total length of other nested
3387
attributes within the AT_ENCR_DATA attribute is a multiple of 16
3388
bytes. As usual, the Length of the Padding attribute includes the
3389
Attribute Type and Attribute Length fields. The length of the
3390
Padding attribute is 4, 8, or 12 bytes. It is chosen so that the
3391
length of the value field of the AT_ENCR_DATA attribute becomes a
3392
multiple of 16 bytes. The actual pad bytes in the value field are
3393
set to zero (00 hexadecimal) on sending. The recipient of the
3394
message MUST verify that the pad bytes are set to zero. If this
3395
verification fails on the peer, then it MUST send the
3396
EAP-Response/SIM/Client-Error packet with the error code "unable to
3397
process packet" to terminate the authentication exchange. If this
3398
verification fails on the server, then the server sends the peer the
3399
EAP-Request/SIM/Notification packet with an AT_NOTIFICATION code that
3400
implies failure to terminate the authentication exchange. The format
3401
of the AT_PADDING attribute is shown below.
3402
3403
0 1 2 3
3404
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
3405
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3406
| AT_PADDING | Length | Padding... |
3407
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
3408
| |
3409
| |
3410
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3411
3412
3413
3414
3415
3416
3417
3418
Haverinen & Salowey Informational [Page 61]
3419
3420
RFC 4186 EAP-SIM Authentication January 2006
3421
3422
3423
10.13. AT_RESULT_IND
3424
3425
The format of the AT_RESULT_IND attribute is shown below.
3426
3427
0 1 2 3
3428
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
3429
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3430
| AT_RESULT_...| Length = 1 | Reserved |
3431
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3432
3433
The value field of this attribute consists of two reserved bytes,
3434
which are set to zero upon sending and ignored upon reception. This
3435
attribute is always sent unencrypted, so it MUST NOT be encapsulated
3436
within the AT_ENCR_DATA attribute.
3437
3438
10.14. AT_MAC
3439
3440
The AT_MAC attribute is used for EAP-SIM message authentication.
3441
Section 8 specifies in which messages AT_MAC MUST be included.
3442
3443
The value field of the AT_MAC attribute contains two reserved bytes
3444
followed by a keyed message authentication code (MAC). The MAC is
3445
calculated over the whole EAP packet and concatenated with optional
3446
message-specific data, with the exception that the value field of the
3447
MAC attribute is set to zero when calculating the MAC. The EAP
3448
packet includes the EAP header that begins with the Code field, the
3449
EAP-SIM header that begins with the Subtype field, and all the
3450
attributes, as specified in Section 8.1. The reserved bytes in
3451
AT_MAC are set to zero when sending and ignored on reception. The
3452
contents of the message-specific data that may be included in the MAC
3453
calculation are specified separately for each EAP-SIM message in
3454
Section 9.
3455
3456
The format of the AT_MAC attribute is shown below.
3457
3458
0 1 2 3
3459
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
3460
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3461
| AT_MAC | Length = 5 | Reserved |
3462
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3463
| |
3464
| MAC |
3465
| |
3466
| |
3467
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3468
3469
3470
3471
3472
3473
3474
Haverinen & Salowey Informational [Page 62]
3475
3476
RFC 4186 EAP-SIM Authentication January 2006
3477
3478
3479
The MAC algorithm is an HMAC-SHA1-128 [RFC2104] keyed hash value.
3480
(The HMAC-SHA1-128 value is obtained from the 20-byte HMAC-SHA1 value
3481
by truncating the output to the first 16 bytes. Hence, the length of
3482
the MAC is 16 bytes. The derivation of the authentication key
3483
(K_aut) used in the calculation of the MAC is specified in Section 7.
3484
3485
When the AT_MAC attribute is included in an EAP-SIM message, the
3486
recipient MUST process the AT_MAC attribute before looking at any
3487
other attributes, except when processing EAP-Request/SIM/Challenge.
3488
The processing of EAP-Request/SIM/Challenge is specified in Section
3489
9.3. If the message authentication code is invalid, then the
3490
recipient MUST ignore all other attributes in the message and operate
3491
as specified in Section 6.3.
3492
3493
10.15. AT_COUNTER
3494
3495
The format of the AT_COUNTER attribute is shown below.
3496
3497
0 1 2 3
3498
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
3499
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3500
| AT_COUNTER | Length = 1 | Counter |
3501
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3502
3503
The value field of the AT_COUNTER attribute consists of a 16-bit
3504
unsigned integer counter value, represented in network byte order.
3505
This attribute MUST always be encrypted by encapsulating it within
3506
the AT_ENCR_DATA attribute.
3507
3508
10.16. AT_COUNTER_TOO_SMALL
3509
3510
The format of the AT_COUNTER_TOO_SMALL attribute is shown below.
3511
3512
0 1 2 3
3513
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
3514
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3515
| AT_COUNTER...| Length = 1 | Reserved |
3516
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3517
3518
The value field of this attribute consists of two reserved bytes,
3519
which are set to zero upon sending and ignored upon reception. This
3520
attribute MUST always be encrypted by encapsulating it within the
3521
AT_ENCR_DATA attribute.
3522
3523
3524
3525
3526
3527
3528
3529
3530
Haverinen & Salowey Informational [Page 63]
3531
3532
RFC 4186 EAP-SIM Authentication January 2006
3533
3534
3535
10.17. AT_NONCE_S
3536
3537
The format of the AT_NONCE_S attribute is shown below.
3538
3539
0 1 2 3
3540
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
3541
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3542
| AT_NONCE_S | Length = 5 | Reserved |
3543
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3544
| |
3545
| |
3546
| NONCE_S |
3547
| |
3548
| |
3549
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3550
3551
The value field of the AT_NONCE_S attribute contains two reserved
3552
bytes followed by a random number freshly generated by the server (16
3553
bytes) for this EAP-SIM fast re-authentication. The random number is
3554
used as a challenge for the peer and also as a seed value for the new
3555
keying material. The reserved bytes are set to zero upon sending and
3556
ignored upon reception. This attribute MUST always be encrypted by
3557
encapsulating it within the AT_ENCR_DATA attribute.
3558
3559
The server MUST NOT re-use the NONCE_S value from any previous
3560
EAP-SIM fast re-authentication exchange. The server SHOULD use a
3561
good source of randomness to generate NONCE_S. Please see [RFC4086]
3562
for more information about generating random numbers for security
3563
applications.
3564
3565
10.18. AT_NOTIFICATION
3566
3567
The format of the AT_NOTIFICATION attribute is shown below.
3568
3569
0 1 2 3
3570
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
3571
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3572
|AT_NOTIFICATION| Length = 1 |S|P| Notification Code |
3573
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3574
3575
The value field of this attribute contains a two-byte notification
3576
code. The first and second bit (S and P) of the notification code
3577
are interpreted as described in Section 6.
3578
3579
The notification code values listed below have been reserved. The
3580
descriptions below illustrate the semantics of the notifications.
3581
3582
3583
3584
3585
3586
Haverinen & Salowey Informational [Page 64]
3587
3588
RFC 4186 EAP-SIM Authentication January 2006
3589
3590
3591
The peer implementation MAY use different wordings when presenting
3592
the notifications to the user. The "requested service" depends on
3593
the environment where EAP-SIM is applied.
3594
3595
0 - General failure after authentication. (Implies failure, used
3596
after successful authentication.)
3597
3598
16384 - General failure. (Implies failure, used before
3599
authentication.)
3600
3601
32768 - Success. User has been successfully authenticated. (Does
3602
not imply failure, used after successful authentication). The usage
3603
of this code is discussed in Section 6.2.
3604
3605
1026 - User has been temporarily denied access to the requested
3606
service. (Implies failure, used after successful authentication.)
3607
3608
1031 - User has not subscribed to the requested service. (Implies
3609
failure, used after successful authentication.)
3610
3611
10.19. AT_CLIENT_ERROR_CODE
3612
3613
The format of the AT_CLIENT_ERROR_CODE attribute is shown below.
3614
3615
0 1 2 3
3616
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
3617
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3618
|AT_CLIENT_ERR..| Length = 1 | Client Error Code |
3619
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3620
3621
The value field of this attribute contains a two-byte client error
3622
code. The following error code values have been reserved.
3623
3624
3625
0 "unable to process packet": a general error code
3626
3627
1 "unsupported version": the peer does not support any of
3628
the versions listed in AT_VERSION_LIST
3629
3630
2 "insufficient number of challenges": the peer's policy
3631
requires more triplets than the server included in AT_RAND
3632
3633
3 "RANDs are not fresh": the peer believes that the RAND
3634
challenges included in AT_RAND were not fresh
3635
3636
3637
3638
3639
3640
3641
3642
Haverinen & Salowey Informational [Page 65]
3643
3644
RFC 4186 EAP-SIM Authentication January 2006
3645
3646
3647
11. IANA Considerations
3648
3649
IANA has assigned the EAP type number 18 for this protocol.
3650
3651
EAP-SIM shares most of the protocol design, such as attributes and
3652
message Subtypes, with EAP-AKA [EAP-AKA]. EAP-SIM protocol numbers
3653
should be administered in the same IANA registry as EAP-AKA. The
3654
initial values are listed in [EAP-AKA] for both protocols, so this
3655
document does not require any new registries or parameter allocation.
3656
As a common registry is used for EAP-SIM and EAP-AKA, the protocol
3657
number allocation policy for both protocols is specified in
3658
[EAP-AKA].
3659
3660
12. Security Considerations
3661
3662
The EAP specification [RFC3748] describes the security
3663
vulnerabilities of EAP, which does not include its own security
3664
mechanisms. This section discusses the claimed security properties
3665
of EAP-SIM, as well as vulnerabilities and security recommendations.
3666
3667
12.1. A3 and A8 Algorithms
3668
3669
The GSM A3 and A8 algorithms are used in EAP-SIM. [GSM-03.20]
3670
specifies the general GSM authentication procedure and the external
3671
interface (inputs and outputs) of the A3 and A8 algorithms. The
3672
operation of these functions falls completely within the domain of an
3673
individual operator, and therefore, the functions are specified by
3674
each operator rather than being fully standardised. The GSM-MILENAGE
3675
algorithm, specified publicly in [3GPP-TS-55.205], is an example
3676
algorithm set for A3 and A8 algorithms.
3677
3678
The security of the A3 and A8 algorithms is important to the security
3679
of EAP-SIM. Some A3/A8 algorithms have been compromised; see [GSM-
3680
Cloning] for discussion about the security of COMP-128 version 1.
3681
Note that several revised versions of the COMP-128 A3/A8 algorithm
3682
have been devised after the publication of these weaknesses and that
3683
the publicly specified GSM-MILENAGE algorithm is not vulnerable to
3684
any known attacks.
3685
3686
12.2. Identity Protection
3687
3688
EAP-SIM includes optional identity privacy support that protects the
3689
privacy of the subscriber identity against passive eavesdropping.
3690
This document only specifies a mechanism to deliver pseudonyms from
3691
the server to the peer as part of an EAP-SIM exchange. Hence, a peer
3692
that has not yet performed any EAP-SIM exchanges does not typically
3693
have a pseudonym available. If the peer does not have a pseudonym
3694
available, then the privacy mechanism cannot be used, but the
3695
3696
3697
3698
Haverinen & Salowey Informational [Page 66]
3699
3700
RFC 4186 EAP-SIM Authentication January 2006
3701
3702
3703
permanent identity will have to be sent in the clear. The terminal
3704
SHOULD store the pseudonym in a non-volatile memory so that it can be
3705
maintained across reboots. An active attacker that impersonates the
3706
network may use the AT_PERMANENT_ID_REQ attribute to attempt to learn
3707
the subscriber's permanent identity. However, as discussed in
3708
Section 4.2.2, the terminal can refuse to send the cleartext
3709
permanent identity if it believes that the network should be able to
3710
recognize the pseudonym.
3711
3712
If the peer and server cannot guarantee that the pseudonym will be
3713
maintained reliably, and identity privacy is required, then
3714
additional protection from an external security mechanism (such as
3715
Protected Extensible Authentication Protocol (PEAP) [PEAP]) may be
3716
used. If an external security mechanism is in use, the identity
3717
privacy features of EAP-SIM may not be useful. The security
3718
considerations of using an external security mechanism with EAP-SIM
3719
are beyond the scope of this document.
3720
3721
12.3. Mutual Authentication and Triplet Exposure
3722
3723
EAP-SIM provides mutual authentication. The peer believes that the
3724
network is authentic because the network can calculate a correct
3725
AT_MAC value in the EAP-Request/SIM/Challenge packet. To calculate
3726
AT_MAC it is sufficient to know the RAND and Kc values from the GSM
3727
triplets (RAND, SRES, Kc) used in the authentication. Because the
3728
network selects the RAND challenges and the triplets, an attacker
3729
that knows n (2 or 3) GSM triplets for the subscriber is able to
3730
impersonate a valid network to the peer. (Some peers MAY employ an
3731
implementation-specific counter-measure against impersonating a valid
3732
network by re-using a previously used RAND; see below.) In other
3733
words, the security of EAP-SIM is based on the secrecy of Kc keys,
3734
which are considered secret intermediate results in the EAP-SIM
3735
cryptographic calculations.
3736
3737
Given physical access to the SIM card, it is easy to obtain any
3738
number of GSM triplets.
3739
3740
Another way to obtain triplets is to mount an attack on the peer
3741
platform via a virus or other malicious piece of software. The peer
3742
SHOULD be protected against triplet querying attacks by malicious
3743
software. Care should be taken not to expose Kc keys to attackers
3744
when they are stored or handled by the peer, or transmitted between
3745
subsystems of the peer. Steps should be taken to limit the
3746
transport, storage, and handling of these values outside a protected
3747
environment within the peer. However, the virus protection of the
3748
peer and the security capabilities of the peer's operating system are
3749
outside the scope of this document.
3750
3751
3752
3753
3754
Haverinen & Salowey Informational [Page 67]
3755
3756
RFC 4186 EAP-SIM Authentication January 2006
3757
3758
3759
The EAP-SIM server typically obtains the triplets from the Home
3760
Location Register (HLR). An attacker might try to obtain triplets by
3761
attacking against the network used between the EAP-SIM server and the
3762
HLR. Care should be taken not to expose Kc keys to attackers when
3763
they are stored or handled by the EAP-SIM server, or transmitted
3764
between the EAP server and the HLR. Steps should be taken to limit
3765
the transport, storage, and handling of these values outside a
3766
protected environment. However, the protection of the communications
3767
between the EAP-SIM server and the HLR is outside the scope of this
3768
document.
3769
3770
If the same SIM credentials are also used for GSM traffic, the
3771
triplets could be revealed in the GSM network; see Section 12.8.
3772
3773
In GSM, the network is allowed to re-use the RAND challenge in
3774
consecutive authentication exchanges. This is not allowed in
3775
EAP-SIM. The EAP-SIM server is mandated to use fresh triplets (RAND
3776
challenges) in consecutive authentication exchanges, as specified in
3777
Section 3. EAP-SIM does not mandate any means for the peer to check
3778
if the RANDs are fresh, so the security of the scheme leans on the
3779
secrecy of the triplets. However, the peer MAY employ
3780
implementation-specific mechanisms to remember some of the previously
3781
used RANDs, and the peer MAY check the freshness of the server's
3782
RANDs. The operation in cases when the peer detects that the RANDs
3783
are not fresh is specified in Section 6.3.1.
3784
3785
Preventing the re-use of authentication vectors has been taken into
3786
account in the design of the UMTS Authentication and Key Agreement
3787
(AKA), which is used in EAP-AKA [EAP-AKA]. In cases when the triplet
3788
re-use properties of EAP-SIM are not considered sufficient, it is
3789
advised to use EAP-AKA.
3790
3791
Note that EAP-SIM mutual authentication is done with the EAP server.
3792
In general, EAP methods do not authenticate the identity or services
3793
provided by the EAP authenticator (if distinct from the EAP server)
3794
unless they provide the so-called channel bindings property. The
3795
vulnerabilities related to this have been discussed in [RFC3748],
3796
[EAP-Keying], [Service-Identity].
3797
3798
EAP-SIM does not provide the channel bindings property, so it only
3799
authenticates the EAP server. However, ongoing work such as
3800
[Service-Identity] may provide such support as an extension to
3801
popular EAP methods such as EAP-TLS, EAP-SIM, or EAP-AKA.
3802
3803
3804
3805
3806
3807
3808
3809
3810
Haverinen & Salowey Informational [Page 68]
3811
3812
RFC 4186 EAP-SIM Authentication January 2006
3813
3814
3815
12.4. Flooding the Authentication Centre
3816
3817
The EAP-SIM server typically obtains authentication vectors from the
3818
Authentication Centre (AuC). EAP-SIM introduces a new usage for the
3819
AuC. The protocols between the EAP-SIM server and the AuC are out of
3820
the scope of this document. However, it should be noted that a
3821
malicious EAP-SIM peer may generate a lot of protocol requests to
3822
mount a denial of service attack. The EAP-SIM server implementation
3823
SHOULD take this into account and SHOULD take steps to limit the
3824
traffic that it generates towards the AuC, preventing the attacker
3825
from flooding the AuC and from extending the denial of service attack
3826
from EAP-SIM to other users of the AuC.
3827
3828
12.5. Key Derivation
3829
3830
EAP-SIM supports key derivation. The key hierarchy is specified in
3831
Section 7. EAP-SIM combines several GSM triplets in order to
3832
generate stronger keying material and stronger AT_MAC values. The
3833
actual strength of the resulting keys depends, among other things, on
3834
operator-specific parameters including authentication algorithms, the
3835
strength of the Ki key, and the quality of the RAND challenges. For
3836
example, some SIM cards generate Kc keys with 10 bits set to zero.
3837
Such restrictions may prevent the concatenation technique from
3838
yielding strong session keys. Because the strength of the Ki key is
3839
128 bits, the ultimate strength of any derived secret key material is
3840
never more than 128 bits.
3841
3842
It should also be noted that a security policy that allows n=2 to be
3843
used may compromise the security of a future policy that requires
3844
three triplets, because adversaries may be able to exploit the
3845
messages exchanged when the weaker policy is applied.
3846
3847
There is no known way to obtain complete GSM triplets by mounting an
3848
attack against EAP-SIM. A passive eavesdropper can learn n*RAND and
3849
AT_MAC and may be able to link this information to the subscriber
3850
identity. An active attacker that impersonates a GSM subscriber can
3851
easily obtain n*RAND and AT_MAC values from the EAP server for any
3852
given subscriber identity. However, calculating the Kc and SRES
3853
values from AT_MAC would require the attacker to reverse the keyed
3854
message authentication code function HMAC-SHA1-128.
3855
3856
As EAP-SIM does not expose any values calculated from an individual
3857
GSM Kc keys, it is not possible to mount a brute force attack on only
3858
one of the Kc keys in EAP-SIM. Therefore, when considering brute
3859
force attacks on the values exposed in EAP-SIM, the effective length
3860
of EAP-SIM session keys is not compromised by the fact that they are
3861
3862
3863
3864
3865
3866
Haverinen & Salowey Informational [Page 69]
3867
3868
RFC 4186 EAP-SIM Authentication January 2006
3869
3870
3871
combined from several shorter keys, i.e., the effective length of 128
3872
bits may be achieved. For additional considerations, see Section
3873
12.8.
3874
3875
12.6. Cryptographic Separation of Keys and Session Independence
3876
3877
The EAP Transient Keys used to protect EAP-SIM packets (K_encr,
3878
K_aut), the Master Session Key, and the Extended Master Session Key
3879
are cryptographically separate in EAP-SIM. An attacker cannot derive
3880
any non-trivial information about any of these keys based on the
3881
other keys. An attacker also cannot calculate the pre-shared secret
3882
(Ki) from the GSM Kc keys, from EAP-SIM K_encr, from EAP-SIM K_aut,
3883
from the Master Session Key, or from the Extended Master Session Key.
3884
3885
Each EAP-SIM exchange generates fresh keying material, and the keying
3886
material exported from the method upon separate EAP-SIM exchanges is
3887
cryptographically separate. The EAP-SIM peer contributes to the
3888
keying material with the NONCE_MT parameter, which must be chosen
3889
freshly for each full authentication exchange. The EAP server is
3890
mandated to choose the RAND challenges freshly for each full
3891
authentication exchange. If either the server or the peer chooses
3892
its random value (NONCE_MT or RAND challenges) freshly, even if the
3893
other entity re-used its value from a previous exchange, then the EAP
3894
Transient Keys, the Master Session Key, and the Extended Master
3895
Session Key will be different and cryptographically separate from the
3896
corresponding values derived upon the previous full authentication
3897
exchange.
3898
3899
On fast re-authentication, freshness of the Master Session Key and
3900
the Extended Master Session Key is provided with a counter
3901
(AT_COUNTER). The same EAP Transient Keys (K_encr, K_aut) that were
3902
used in the full authentication exchange are used to protect the EAP
3903
negotiation. However, replay and integrity protection across all the
3904
fast re-authentication exchanges that use the same EAP Transient Keys
3905
is provided with AT_COUNTER.
3906
3907
[RFC3748] defines session independence as the "demonstration that
3908
passive attacks (such as capture of the EAP conversation) or active
3909
attacks (including compromise of the MSK or EMSK) do not enable
3910
compromise of subsequent or prior MSKs or EMSKs". Because the MSKs
3911
and EMSKs are separate between EAP exchanges, EAP-SIM supports this
3912
security claim.
3913
3914
It should be noted that [Patel-2003], which predates [RFC3748], uses
3915
a slightly different meaning for session independence. The EAP-SIM
3916
protocol does not allow the peer to ensure that different Kc key
3917
values would be used in different exchanges. Only the server is able
3918
to ensure that fresh RANDs, and therefore, fresh Kc keys are used.
3919
3920
3921
3922
Haverinen & Salowey Informational [Page 70]
3923
3924
RFC 4186 EAP-SIM Authentication January 2006
3925
3926
3927
Hence, the peer cannot guarantee EAP-SIM sessions to be independent
3928
with regard to the internal Kc values. However, in EAP-SIM, the Kc
3929
keys are considered to be secret intermediate results, which are not
3930
exported outside the method. See Section 12.3 for more information
3931
about RAND re-use.
3932
3933
12.7. Dictionary Attacks
3934
3935
Because EAP-SIM is not a password protocol, it is not vulnerable to
3936
dictionary attacks. (The pre-shared symmetric secret stored on the
3937
SIM card is not a passphrase, nor is it derived from a passphrase.)
3938
3939
12.8. Credentials Re-use
3940
3941
EAP-SIM cannot prevent attacks over the GSM or GPRS radio networks.
3942
If the same SIM credentials are also used in GSM or GPRS, it is
3943
possible to mount attacks over the cellular interface.
3944
3945
A passive attacker can eavesdrop GSM or GPRS traffic and obtain RAND,
3946
SRES pairs. He can then use a brute force attack or other
3947
cryptanalysis techniques to obtain the 64-bit Kc keys used to encrypt
3948
the GSM or GPRS data. This makes it possible to attack each 64-bit
3949
key separately.
3950
3951
An active attacker can mount a "rogue GSM/GPRS base station attack",
3952
replaying previously seen RAND challenges to obtain SRES values. He
3953
can then use a brute force attack to obtain the Kc keys. If
3954
successful, the attacker can impersonate a valid network or decrypt
3955
previously seen traffic, because EAP-SIM does not provide perfect
3956
forward secrecy (PFS).
3957
3958
Due to several weaknesses in the GSM encryption algorithms, the
3959
effective key strength of the Kc keys is much less than the expected
3960
64 bits (no more than 40 bits if the A5/1 GSM encryption algorithm is
3961
used; as documented in [Barkan-2003], an active attacker can force
3962
the peer to use the weaker A5/2 algorithm that can be broken in less
3963
than a second).
3964
3965
Because the A5 encryption algorithm is not used in EAP-SIM, and
3966
because EAP-SIM does not expose any values calculated from individual
3967
Kc keys, it should be noted that these attacks are not possible if
3968
the SIM credentials used in EAP-SIM are not shared in GSM/GPRS.
3969
3970
At the time this document was written, the 3rd Generation Partnership
3971
Project (3GPP) has started to work on fixes to these A5
3972
vulnerabilities. One of the solution proposals discussed in 3GPP is
3973
integrity-protected A5 version negotiation, which would require the
3974
base station to prove knowledge of the Kc key before the terminal
3975
3976
3977
3978
Haverinen & Salowey Informational [Page 71]
3979
3980
RFC 4186 EAP-SIM Authentication January 2006
3981
3982
3983
sends any values calculated from the Kc to the network. Another
3984
proposal is so-called special RANDs, where some bits of the RAND
3985
challenge would be used for cryptographic separation by indicating
3986
the allowed use of the triplet, such as the allowed A5 algorithm in
3987
GSM or the fact that the triplet is intended for EAP-SIM. This is
3988
currently a work in progress, and the mechanisms have not been
3989
selected yet.
3990
3991
12.9. Integrity and Replay Protection, and Confidentiality
3992
3993
AT_MAC, AT_IV, AT_ENCR_DATA, and AT_COUNTER attributes are used to
3994
provide integrity, replay and confidentiality protection for EAP-SIM
3995
requests and responses. Integrity protection with AT_MAC includes
3996
the EAP header. These attributes cannot be used during the
3997
EAP/SIM/Start roundtrip. However, the protocol values (user identity
3998
string, NONCE_MT, and version negotiation parameters) are
3999
(implicitly) protected by later EAP-SIM messages by including them in
4000
key derivation.
4001
4002
Integrity protection (AT_MAC) is based on a keyed message
4003
authentication code. Confidentiality (AT_ENCR_DATA and AT_IV) is
4004
based on a block cipher.
4005
4006
Confidentiality protection is applied only to a part of the protocol
4007
fields. The table of attributes in Section 10.1 summarizes which
4008
fields are confidentiality-protected. It should be noted that the
4009
error and notification code attributes AT_CLIENT_ERROR_CODE and
4010
AT_NOTIFICATION are not confidential, but they are transmitted in the
4011
clear. Identity protection is discussed in Section 12.2.
4012
4013
On full authentication, replay protection of the EAP exchange is
4014
provided by the RAND values from the underlying GSM authentication
4015
scheme and the use of the NONCE_MT value. Protection against replays
4016
of EAP-SIM messages is also based on the fact that messages that can
4017
include AT_MAC can only be sent once with a certain EAP-SIM Subtype,
4018
and on the fact that a different K_aut key will be used for
4019
calculating AT_MAC in each full authentication exchange.
4020
4021
On fast re-authentication, a counter included in AT_COUNTER and a
4022
server random nonce is used to provide replay protection. The
4023
AT_COUNTER attribute is also included in EAP-SIM notifications if it
4024
is used after successful authentication in order to provide replay
4025
protection between re-authentication exchanges.
4026
4027
Because EAP-SIM is not a tunneling method, EAP-Request/Notification,
4028
EAP-Response/Notification, EAP-Success, or EAP-Failure packets are
4029
not confidential, integrity-protected, or replay-protected in
4030
EAP-SIM. On physically insecure networks, this may enable an
4031
4032
4033
4034
Haverinen & Salowey Informational [Page 72]
4035
4036
RFC 4186 EAP-SIM Authentication January 2006
4037
4038
4039
attacker to send false notifications to the peer and to mount denial
4040
of service attacks by spoofing these packets. As discussed in
4041
Section 6.3, the peer will only accept EAP-Success after the peer
4042
successfully authenticates the server. Hence, the attacker cannot
4043
force the peer to believe successful mutual authentication has
4044
occurred until the peer successfully authenticates the server or
4045
after the peer fails to authenticate the server.
4046
4047
The security considerations of EAP-SIM result indications are covered
4048
in Section 12.11
4049
4050
An eavesdropper will see the EAP-Request/Notification,
4051
EAP-Response/Notification, EAP-Success, and EAP-Failure packets sent
4052
in the clear. With EAP-SIM, confidential information MUST NOT be
4053
transmitted in EAP Notification packets.
4054
4055
12.10. Negotiation Attacks
4056
4057
EAP-SIM does not protect the EAP-Response/Nak packet. Because
4058
EAP-SIM does not protect the EAP method negotiation, EAP method
4059
downgrading attacks may be possible, especially if the user uses the
4060
same identity with EAP-SIM and other EAP methods.
4061
4062
EAP-SIM includes a version negotiation procedure. In EAP-SIM the
4063
keying material derivation includes the version list and selected
4064
version to ensure that the protocol cannot be downgraded and that the
4065
peer and server use the same version of EAP-SIM.
4066
4067
EAP-SIM does not support ciphersuite negotiation.
4068
4069
12.11. Protected Result Indications
4070
4071
EAP-SIM supports optional protected success indications and
4072
acknowledged failure indications. If a failure occurs after
4073
successful authentication, then the EAP-SIM failure indication is
4074
integrity- and replay-protected.
4075
4076
Even if an EAP-Failure packet is lost when using EAP-SIM over an
4077
unreliable medium, then the EAP-SIM failure indications will help
4078
ensure that the peer and EAP server will know the other party's
4079
authentication decision. If protected success indications are used,
4080
then the loss of Success packet will also be addressed by the
4081
acknowledged, integrity- and replay-protected EAP-SIM success
4082
indication. If the optional success indications are not used, then
4083
the peer may end up believing that the server succeeded
4084
authentication, when it actually failed. Since access will not be
4085
4086
4087
4088
4089
4090
Haverinen & Salowey Informational [Page 73]
4091
4092
RFC 4186 EAP-SIM Authentication January 2006
4093
4094
4095
granted in this case, protected result indications are not needed
4096
unless the client is not able to realize it does not have access for
4097
an extended period of time.
4098
4099
12.12. Man-in-the-Middle Attacks
4100
4101
In order to avoid man-in-the-middle attacks and session hijacking,
4102
user data SHOULD be integrity-protected on physically insecure
4103
networks. The EAP-SIM Master Session Key, or keys derived from it,
4104
MAY be used as the integrity protection keys, or, if an external
4105
security mechanism such as PEAP is used, then the link integrity
4106
protection keys MAY be derived by the external security mechanism.
4107
4108
There are man-in-the-middle attacks associated with the use of any
4109
EAP method within a tunneled protocol. For instance, an early
4110
version of PEAP [PEAP-02] was vulnerable to this attack. This
4111
specification does not address these attacks. If EAP-SIM is used
4112
with a tunneling protocol, there should be cryptographic binding
4113
provided between the protocol and EAP-SIM to prevent
4114
man-in-the-middle attacks through rogue authenticators being able to
4115
setup one-way authenticated tunnels. For example, newer versions of
4116
PEAP include such cryptographic binding. The EAP-SIM Master Session
4117
Key MAY be used to provide the cryptographic binding. However, the
4118
mechanism by which the binding is provided depends on the tunneling
4119
protocol and is beyond the scope of this document.
4120
4121
12.13. Generating Random Numbers
4122
4123
An EAP-SIM implementation SHOULD use a good source of randomness to
4124
generate the random numbers required in the protocol. Please see
4125
[RFC4086] for more information on generating random numbers for
4126
security applications.
4127
4128
13. Security Claims
4129
4130
This section provides the security claims required by [RFC3748].
4131
4132
Auth. mechanism: EAP-SIM is based on the GSM SIM mechanism, which is
4133
a challenge/response authentication and key agreement mechanism based
4134
on a symmetric 128-bit pre-shared secret. EAP-SIM also makes use of
4135
a peer challenge to provide mutual authentication.
4136
4137
Ciphersuite negotiation: No
4138
4139
Mutual authentication: Yes (Section 12.3)
4140
4141
Integrity protection: Yes (Section 12.9)
4142
4143
4144
4145
4146
Haverinen & Salowey Informational [Page 74]
4147
4148
RFC 4186 EAP-SIM Authentication January 2006
4149
4150
4151
Replay protection: Yes (Section 12.9)
4152
4153
Confidentiality: Yes, except method-specific success and failure
4154
indications (Section 12.2, Section 12.9)
4155
4156
Key derivation: Yes
4157
4158
Key strength: EAP-SIM supports key derivation with 128-bit effective
4159
key strength (Section 12.5). However, as discussed in Section 11, if
4160
the same credentials are used in GSM/GPRS and in EAP-SIM, then the
4161
key strength may be reduced considerably, basically to the same level
4162
as in GSM, by mounting attacks over GSM/GPRS. For example an active
4163
attack using a false GSM/GPRS base station reduces the effective key
4164
strength to almost zero.
4165
4166
Description of key hierarchy: Please see Section 7.
4167
4168
Dictionary attack protection: N/A (Section 12.7)
4169
4170
Fast reconnect: Yes
4171
4172
Cryptographic binding: N/A
4173
4174
Session independence: Yes (Section 12.6)
4175
4176
Fragmentation: No
4177
4178
Channel binding: No
4179
4180
Indication of vulnerabilities: Vulnerabilities are discussed in
4181
Section 12.
4182
4183
14. Acknowledgements and Contributions
4184
4185
14.1. Contributors
4186
4187
In addition to the editors, Nora Dabbous, Jose Puthenkulam, and
4188
Prasanna Satarasinghe were significant contributors to this document.
4189
4190
Pasi Eronen and Jukka-Pekka Honkanen contributed Appendix A.
4191
4192
14.2. Acknowledgements
4193
4194
Juha Ala-Laurila, N. Asokan, Jan-Erik Ekberg, Patrik Flykt,
4195
Jukka-Pekka Honkanen, Antti Kuikka, Jukka Latva, Lassi Lehtinen, Jyri
4196
Rinnemaa, Timo Takamaki, and Raimo Vuonnala contributed many original
4197
ideas and concepts to this protocol.
4198
4199
4200
4201
4202
Haverinen & Salowey Informational [Page 75]
4203
4204
RFC 4186 EAP-SIM Authentication January 2006
4205
4206
4207
N. Asokan, Pasi Eronen, and Jukka-Pekka Honkanen contributed and
4208
helped in innumerable ways during the development of the protocol.
4209
4210
Valtteri Niemi and Kaisa Nyberg contributed substantially to the
4211
design of the key derivation and the fast re-authentication
4212
procedure, and have also provided their cryptographic expertise in
4213
many discussions related to this protocol.
4214
4215
Simon Blake-Wilson provided very helpful comments on key derivation
4216
and version negotiation.
4217
4218
Thanks to Greg Rose for his very valuable comments to an early
4219
version of this specification [S3-020125], and for reviewing and
4220
providing very useful comments on version 12.
4221
4222
Thanks to Bernard Aboba, Vladimir Alperovich, Florent Bersani,
4223
Jacques Caron, Gopal Dommety, Augustin Farrugia, Mark Grayson, Max de
4224
Groot, Prakash Iyer, Nishi Kant, Victor Lortz, Jouni Malinen, Sarvar
4225
Patel, Tom Porcher, Michael Richardson, Stefan Schroeder, Uma
4226
Shankar, Jesse Walker, and Thomas Wieland for their contributions and
4227
critiques. Special thanks to Max for proposing improvements to the
4228
MAC calculation.
4229
4230
Thanks to Glen Zorn for reviewing this document and for providing
4231
very useful comments on the protocol.
4232
4233
Thanks to Sarvar Patel for his review of the protocol [Patel-2003].
4234
4235
Thanks to Bernard Aboba for reviewing this document for RFC 3748
4236
compliance.
4237
4238
The identity privacy support is based on the identity privacy support
4239
of [EAP-SRP]. The attribute format is based on the extension format
4240
of Mobile IPv4 [RFC3344].
4241
4242
This protocol has been partly developed in parallel with EAP-AKA
4243
[EAP-AKA], and hence this specification incorporates many ideas from
4244
Jari Arkko.
4245
4246
4247
4248
4249
4250
4251
4252
4253
4254
4255
4256
4257
4258
Haverinen & Salowey Informational [Page 76]
4259
4260
RFC 4186 EAP-SIM Authentication January 2006
4261
4262
4263
14.2.1. Contributors' Addresses
4264
4265
Nora Dabbous
4266
Gemplus
4267
34 rue Guynemer
4268
92447 Issy les Moulineaux
4269
France
4270
4271
Phone: +33 1 4648 2000
4272
EMail: nora.dabbous@gemplus.com
4273
4274
4275
Jose Puthenkulam
4276
Intel Corporation
4277
2111 NE 25th Avenue, JF2-58
4278
Hillsboro, OR 97124
4279
USA
4280
4281
Phone: +1 503 264 6121
4282
EMail: jose.p.puthenkulam@intel.com
4283
4284
4285
Prasanna Satarasinghe
4286
Transat Technologies
4287
180 State Street, Suite 240
4288
Southlake, TX 76092
4289
USA
4290
4291
Phone: + 1 817 4814412
4292
EMail: prasannas@transat-tech.com
4293
4294
4295
4296
4297
4298
4299
4300
4301
4302
4303
4304
4305
4306
4307
4308
4309
4310
4311
4312
4313
4314
Haverinen & Salowey Informational [Page 77]
4315
4316
RFC 4186 EAP-SIM Authentication January 2006
4317
4318
4319
15. References
4320
4321
15.1. Normative References
4322
4323
[GSM-03.20] European Telecommunications Standards Institute,
4324
"GSM Technical Specification GSM 03.20 (ETS 300
4325
534): "Digital cellular telecommunication system
4326
(Phase 2); Security related network functions"",
4327
August 1997.
4328
4329
[RFC2119] Bradner, S., "Key words for use in RFCs to
4330
Indicate Requirement Levels", BCP 14, RFC 2119,
4331
March 1997.
4332
4333
[GSM-03.03] European Telecommunications Standards Institute,
4334
"GSM Technical Specification GSM 03.03 (ETS 300
4335
523): "Digital cellular telecommunication system
4336
(Phase 2); Numbering, addressing and
4337
identification"", April 1997.
4338
4339
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC:
4340
Keyed-Hashing for Message Authentication", RFC
4341
2104, February 1997.
4342
4343
[RFC4282] Aboba, B., Beadles, M., Arkko, J., and P. Eronen,
4344
"The Network Access Identifier", RFC 4282,
4345
December 2005.
4346
4347
[AES] National Institute of Standards and Technology,
4348
"Federal Information Processing Standards (FIPS)
4349
Publication 197, "Advanced Encryption Standard
4350
(AES)"", November 2001.
4351
http://csrc.nist.gov/publications/fips/fips197/
4352
fips-197.pdf
4353
4354
[CBC] National Institute of Standards and Technology,
4355
"NIST Special Publication 800-38A, "Recommendation
4356
for Block Cipher Modes of Operation - Methods and
4357
Techniques"", December 2001.
4358
http://csrc.nist.gov/publications/nistpubs/
4359
800-38a/sp800-38a.pdf
4360
4361
[SHA-1] National Institute of Standards and Technology,
4362
U.S. Department of Commerce, "Federal Information
4363
Processing Standard (FIPS) Publication 180-1,
4364
"Secure Hash Standard"", April 1995.
4365
4366
4367
4368
4369
4370
Haverinen & Salowey Informational [Page 78]
4371
4372
RFC 4186 EAP-SIM Authentication January 2006
4373
4374
4375
[PRF] National Institute of Standards and Technology,
4376
"Federal Information Processing Standards (FIPS)
4377
Publication 186-2 (with change notice); Digital
4378
Signature Standard (DSS)", January 2000.
4379
Available on-line at:
4380
http://csrc.nist.gov/publications/
4381
fips/fips186-2/fips186-2-change1.pdf
4382
4383
[RFC3629] Yergeau, F., "UTF-8, a transformation format of
4384
ISO 10646", STD 63, RFC 3629, November 2003.
4385
4386
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J.,
4387
and H. Levkowetz, "Extensible Authentication
4388
Protocol (EAP)", RFC 3748, June 2004.
4389
4390
[EAP-AKA] Arkko, J. and H. Haverinen, "Extensible
4391
Authentication Protocol Method for 3rd Generation
4392
Authentication and Key Agreement (EAP-AKA)", RFC
4393
4187, January 2006.
4394
4395
15.2. Informative References
4396
4397
[3GPP-TS-23.003] 3rd Generation Partnership Project, "3GPP
4398
Technical Specification 3GPP TS 23.003 V6.8.0:
4399
"3rd Generation Parnership Project; Technical
4400
Specification Group Core Network; Numbering,
4401
addressing and identification (Release 6)"",
4402
December 2005.
4403
4404
[3GPP-TS-55.205] 3rd Generation Partnership Project, "3GPP
4405
Technical Specification 3GPP TS 55.205 V 6.0.0:
4406
"3rd Generation Partnership Project; Technical
4407
Specification Group Services and System Aspects;
4408
Specification of the GSM-MILENAGE Algorithms: An
4409
example algorithm set for the GSM Authentication
4410
and Key Generation functions A3 and A8 (Release
4411
6)"", December 2002.
4412
4413
[PEAP] Palekar, A., Simon, D., Zorn, G., Salowey, J.,
4414
Zhou, H., and S. Josefsson, "Protected EAP
4415
Protocol (PEAP) Version 2", Work in Progress,
4416
October 2004.
4417
4418
[PEAP-02] Anderson, H., Josefsson, S., Zorn, G., Simon, D.,
4419
and A. Palekar, "Protected EAP Protocol (PEAP)",
4420
Work in Progress, February 2002.
4421
4422
4423
4424
4425
4426
Haverinen & Salowey Informational [Page 79]
4427
4428
RFC 4186 EAP-SIM Authentication January 2006
4429
4430
4431
[EAP-Keying] Aboba, B., Simon, D., Arkko, J., Eronen, P., and
4432
H. Levkowetz, "Extensible Authentication Protocol
4433
(EAP) Key Management Framework", Work in Progress,
4434
October 2005.
4435
4436
[Service-Identity] Arkko, J. and P. Eronen, "Authenticated Service
4437
Information for the Extensible Authentication
4438
Protocol (EAP)", Work in Progress, October 2004.
4439
4440
[RFC4086] Eastlake, D., 3rd, Schiller, J., and S. Crocker,
4441
"Randomness Requirements for Security", BCP 106,
4442
RFC 4086, June 2005.
4443
4444
[S3-020125] Qualcomm, "Comments on draft EAP/SIM, 3rd
4445
Generation Partnership Project document 3GPP TSG
4446
SA WG3 Security S3#22, S3-020125", February 2002.
4447
4448
[RFC3344] Perkins, C., "IP Mobility Support for IPv4", RFC
4449
3344, August 2002.
4450
4451
[RFC2548] Zorn, G., "Microsoft Vendor-specific RADIUS
4452
Attributes ", RFC 2548, March 1999.
4453
4454
[EAP-SRP] Carlson, J., Aboba, B., and H. Haverinen, "EAP
4455
SRP-SHA1 Authentication Protocol", Work in
4456
Progress, July 2001.
4457
4458
[GSM-Cloning] Wagner, D., "GSM Cloning". Web page about
4459
COMP-128 version 1 vulnerabilities, available at
4460
http://www.isaac.cs.berkeley.edu/isaac/gsm.html
4461
4462
[Barkan-2003] Barkan, E., Biham, E., and N. Keller, "Instant
4463
Ciphertext-Only Cryptanalysis of GSM Encrypted
4464
Communications". available on-line at
4465
http://cryptome.org/gsm-crack-bbk.pdf
4466
4467
[Patel-2003] Patel, S., "Analysis of EAP-SIM Session Key
4468
Agreement". Posted to the EAP mailing list 29
4469
May,2003. http://
4470
mail.frascone.com/pipermail/public/eap/2003-May/
4471
001267.html
4472
4473
4474
4475
4476
4477
4478
4479
4480
4481
4482
Haverinen & Salowey Informational [Page 80]
4483
4484
RFC 4186 EAP-SIM Authentication January 2006
4485
4486
4487
Appendix A. Test Vectors
4488
4489
Test vectors for the NIST FIPS 186-2 pseudo-random number generator
4490
[PRF] are available at the following URL:
4491
http://csrc.nist.gov/encryption/dss/Examples-1024bit.pdf
4492
4493
The following examples show the contents of EAP-SIM packets on full
4494
authentication and fast re-authentication.
4495
4496
A.1. EAP-Request/Identity
4497
4498
The first packet is a plain Identity Request:
4499
4500
01 ; Code: Request
4501
00 ; Identifier: 0
4502
00 05 ; Length: 5 octets
4503
01 ; Type: Identity
4504
4505
A.2. EAP-Response/Identity
4506
4507
The client's identity is "1244070100000001@eapsim.foo", so it
4508
responds with the following packet:
4509
4510
02 ; Code: Response
4511
00 ; Identifier: 0
4512
00 20 ; Length: 32 octets
4513
01 ; Type: Identity
4514
31 32 34 34 ; "1244070100000001@eapsim.foo"
4515
30 37 30 31
4516
30 30 30 30
4517
30 30 30 31
4518
40 65 61 70
4519
73 69 6d 2e
4520
66 6f 6f
4521
4522
4523
4524
4525
4526
4527
4528
4529
4530
4531
4532
4533
4534
4535
4536
4537
4538
Haverinen & Salowey Informational [Page 81]
4539
4540
RFC 4186 EAP-SIM Authentication January 2006
4541
4542
4543
A.3. EAP-Request/SIM/Start
4544
4545
The server's first packet looks like this:
4546
4547
01 ; Code: Request
4548
01 ; Identifier: 1
4549
00 10 ; Length: 16 octets
4550
12 ; Type: EAP-SIM
4551
0a ; EAP-SIM subtype: Start
4552
00 00 ; (reserved)
4553
0f ; Attribute type: AT_VERSION_LIST
4554
02 ; Attribute length: 8 octets (2*4)
4555
00 02 ; Actual version list length: 2 octets
4556
00 01 ; Version: 1
4557
00 00 ; (attribute padding)
4558
4559
A.4. EAP-Response/SIM/Start
4560
4561
The client selects a nonce and responds with the following packet:
4562
4563
02 ; Code: Response
4564
01 ; Identifier: 1
4565
00 20 ; Length: 32 octets
4566
12 ; Type: EAP-SIM
4567
0a ; EAP-SIM subtype: Start
4568
00 00 ; (reserved)
4569
07 ; Attribute type: AT_NONCE_MT
4570
05 ; Attribute length: 20 octets (5*4)
4571
00 00 ; (reserved)
4572
01 23 45 67 ; NONCE_MT value
4573
89 ab cd ef
4574
fe dc ba 98
4575
76 54 32 10
4576
10 ; Attribute type: AT_SELECTED_VERSION
4577
01 ; Attribute length: 4 octets (1*4)
4578
00 01 ; Version: 1
4579
4580
4581
4582
4583
4584
4585
4586
4587
4588
4589
4590
4591
4592
4593
4594
Haverinen & Salowey Informational [Page 82]
4595
4596
RFC 4186 EAP-SIM Authentication January 2006
4597
4598
4599
A.5. EAP-Request/SIM/Challenge
4600
4601
Next, the server selects three authentication triplets
4602
4603
(RAND1,SRES1,Kc1) = (10111213 14151617 18191a1b 1c1d1e1f,
4604
d1d2d3d4,
4605
a0a1a2a3 a4a5a6a7)
4606
(RAND2,SRES2,Kc2) = (20212223 24252627 28292a2b 2c2d2e2f,
4607
e1e2e3e4,
4608
b0b1b2b3 b4b5b6b7)
4609
(RAND3,SRES3,Kc3) = (30313233 34353637 38393a3b 3c3d3e3f,
4610
f1f2f3f4,
4611
c0c1c2c3 c4c5c6c7)
4612
4613
Next, the MK is calculated as specified in Section 7*.
4614
4615
MK = e576d5ca 332e9930 018bf1ba ee2763c7 95b3c712
4616
4617
And the other keys are derived using the PRNG:
4618
4619
K_encr = 536e5ebc 4465582a a6a8ec99 86ebb620
4620
K_aut = 25af1942 efcbf4bc 72b39434 21f2a974
4621
MSK = 39d45aea f4e30601 983e972b 6cfd46d1
4622
c3637733 65690d09 cd44976b 525f47d3
4623
a60a985e 955c53b0 90b2e4b7 3719196a
4624
40254296 8fd14a88 8f46b9a7 886e4488
4625
EMSK = 5949eab0 fff69d52 315c6c63 4fd14a7f
4626
0d52023d 56f79698 fa6596ab eed4f93f
4627
bb48eb53 4d985414 ceed0d9a 8ed33c38
4628
7c9dfdab 92ffbdf2 40fcecf6 5a2c93b9
4629
4630
Next, the server selects a pseudonym and a fast re-authentication
4631
identity (in this case, "w8w49PexCazWJ&xCIARmxuMKht5S1sxR
4632
DqXSEFBEg3DcZP9cIxTe5J4OyIwNGVzxeJOU1G" and
4633
"Y24fNSrz8BP274jOJaF17WfxI8YO7QX0
4634
0pMXk9XMMVOw7broaNhTczuFq53aEpOkk3L0dm@eapsim.foo", respectively).
4635
4636
4637
4638
4639
4640
4641
4642
4643
4644
4645
4646
4647
4648
4649
4650
Haverinen & Salowey Informational [Page 83]
4651
4652
RFC 4186 EAP-SIM Authentication January 2006
4653
4654
4655
The following plaintext will be encrypted and stored in the
4656
AT_ENCR_DATA attribute:
4657
4658
84 ; Attribute type: AT_NEXT_PSEUDONYM
4659
13 ; Attribute length: 76 octets (19*4)
4660
00 46 ; Actual pseudonym length: 70 octets
4661
77 38 77 34 39 50 65 78 43 61 7a 57 4a 26 78 43
4662
49 41 52 6d 78 75 4d 4b 68 74 35 53 31 73 78 52
4663
44 71 58 53 45 46 42 45 67 33 44 63 5a 50 39 63
4664
49 78 54 65 35 4a 34 4f 79 49 77 4e 47 56 7a 78
4665
65 4a 4f 55 31 47
4666
00 00 ; (attribute padding)
4667
85 ; Attribute type: AT_NEXT_REAUTH_ID
4668
16 ; Attribute length: 88 octets (22*4)
4669
00 51 ; Actual re-auth identity length: 81 octets
4670
59 32 34 66 4e 53 72 7a 38 42 50 32 37 34 6a 4f
4671
4a 61 46 31 37 57 66 78 49 38 59 4f 37 51 58 30
4672
30 70 4d 58 6b 39 58 4d 4d 56 4f 77 37 62 72 6f
4673
61 4e 68 54 63 7a 75 46 71 35 33 61 45 70 4f 6b
4674
6b 33 4c 30 64 6d 40 65 61 70 73 69 6d 2e 66 6f
4675
6f
4676
00 00 00 ; (attribute padding)
4677
06 ; Attribute type: AT_PADDING
4678
03 ; Attribute length: 12 octets (3*4)
4679
00 00 00 00
4680
00 00 00 00
4681
00 00
4682
4683
The EAP packet looks like this:
4684
4685
01 ; Code: Request
4686
02 ; Identifier: 2
4687
01 18 ; Length: 280 octets
4688
12 ; Type: EAP-SIM
4689
0b ; EAP-SIM subtype: Challenge
4690
00 00 ; (reserved)
4691
01 ; Attribute type: AT_RAND
4692
0d ; Attribute length: 52 octets (13*4)
4693
00 00 ; (reserved)
4694
10 11 12 13 ; first RAND
4695
14 15 16 17
4696
18 19 1a 1b
4697
1c 1d 1e 1f
4698
20 21 22 23 ; second RAND
4699
24 25 26 27
4700
28 29 2a 2b
4701
2c 2d 2e 2f
4702
4703
4704
4705
4706
Haverinen & Salowey Informational [Page 84]
4707
4708
RFC 4186 EAP-SIM Authentication January 2006
4709
4710
4711
30 31 32 33 ; third RAND
4712
34 35 36 37
4713
38 39 3a 3b
4714
3c 3d 3e 3f
4715
81 ; Attribute type: AT_IV
4716
05 ; Attribute length: 20 octets (5*4)
4717
00 00 ; (reserved)
4718
9e 18 b0 c2 ; IV value
4719
9a 65 22 63
4720
c0 6e fb 54
4721
dd 00 a8 95
4722
82 ; Attribute type: AT_ENCR_DATA
4723
2d ; Attribute length: 180 octets (45*4)
4724
00 00 ; (reserved)
4725
55 f2 93 9b bd b1 b1 9e a1 b4 7f c0 b3 e0 be 4c
4726
ab 2c f7 37 2d 98 e3 02 3c 6b b9 24 15 72 3d 58
4727
ba d6 6c e0 84 e1 01 b6 0f 53 58 35 4b d4 21 82
4728
78 ae a7 bf 2c ba ce 33 10 6a ed dc 62 5b 0c 1d
4729
5a a6 7a 41 73 9a e5 b5 79 50 97 3f c7 ff 83 01
4730
07 3c 6f 95 31 50 fc 30 3e a1 52 d1 e1 0a 2d 1f
4731
4f 52 26 da a1 ee 90 05 47 22 52 bd b3 b7 1d 6f
4732
0c 3a 34 90 31 6c 46 92 98 71 bd 45 cd fd bc a6
4733
11 2f 07 f8 be 71 79 90 d2 5f 6d d7 f2 b7 b3 20
4734
bf 4d 5a 99 2e 88 03 31 d7 29 94 5a ec 75 ae 5d
4735
43 c8 ed a5 fe 62 33 fc ac 49 4e e6 7a 0d 50 4d
4736
0b ; Attribute type: AT_MAC
4737
05 ; Attribute length: 20 octets (5*4)
4738
00 00 ; (reserved)
4739
fe f3 24 ac ; MAC value
4740
39 62 b5 9f
4741
3b d7 82 53
4742
ae 4d cb 6a
4743
4744
The MAC is calculated over the EAP packet above (with MAC value set
4745
to zero), followed by the NONCE_MT value (a total of 296 bytes).
4746
4747
4748
4749
4750
4751
4752
4753
4754
4755
4756
4757
4758
4759
4760
4761
4762
Haverinen & Salowey Informational [Page 85]
4763
4764
RFC 4186 EAP-SIM Authentication January 2006
4765
4766
4767
A.6. EAP-Response/SIM/Challenge
4768
4769
The client's response looks like this:
4770
4771
02 ; Code: Response
4772
02 ; Identifier: 2
4773
00 1c ; Length: 28 octets
4774
12 ; Type: EAP-SIM
4775
0b ; EAP-SIM subtype: Challenge
4776
00 00 ; (reserved)
4777
0b ; Attribute type: AT_MAC
4778
05 ; Attribute length: 20 octets (5*4)
4779
00 00 ; (reserved)
4780
f5 6d 64 33 ; MAC value
4781
e6 8e d2 97
4782
6a c1 19 37
4783
fc 3d 11 54
4784
4785
The MAC is calculated over the EAP packet above (with MAC value set
4786
to zero), followed by the SRES values (a total of 40 bytes).
4787
4788
A.7. EAP-Success
4789
4790
The last packet is an EAP-Success:
4791
4792
03 ; Code: Success
4793
02 ; Identifier: 2
4794
00 04 ; Length: 4 octets
4795
4796
A.8. Fast Re-authentication
4797
4798
When performing fast re-authentication, the EAP-Request/Identity
4799
packet is the same as usual. The EAP-Response/Identity contains the
4800
fast re-authentication identity (from AT_ENCR_DATA attribute above):
4801
4802
02 ; Code: Response
4803
00 ; Identifier: 0
4804
00 56 ; Length: 86 octets
4805
01 ; Type: Identity
4806
59 32 34 66 4e 53 72 7a 38 42 50 32 37 34 6a 4f
4807
4a 61 46 31 37 57 66 78 49 38 59 4f 37 51 58 30
4808
30 70 4d 58 6b 39 58 4d 4d 56 4f 77 37 62 72 6f
4809
61 4e 68 54 63 7a 75 46 71 35 33 61 45 70 4f 6b
4810
6b 33 4c 30 64 6d 40 65 61 70 73 69 6d 2e 66 6f
4811
6f
4812
4813
4814
4815
4816
4817
4818
Haverinen & Salowey Informational [Page 86]
4819
4820
RFC 4186 EAP-SIM Authentication January 2006
4821
4822
4823
A.9. EAP-Request/SIM/Re-authentication
4824
4825
The server recognizes the reauthentication identity, so it will
4826
respond with EAP-Request/SIM/Re-authentication. It retrieves the
4827
associated counter value, generates a nonce, and picks a new
4828
reauthentication identity (in this case,
4829
"uta0M0iyIsMwWp5TTdSdnOLvg2XDVf21OYt1vnfiMcs5dnIDHOIFVavIRzMR
4830
yzW6vFzdHW@eapsim.foo").
4831
4832
The following plaintext will be encrypted and stored in the
4833
AT_ENCR_DATA attribute. Note that AT_PADDING is not used because the
4834
length of the plaintext is a multiple of 16 bytes.
4835
4836
13 ; Attribute type: AT_COUNTER
4837
01 ; Attribute length: 4 octets (1*4)
4838
00 01 ; Counter value
4839
15 ; Attribute type: AT_NONCE_S
4840
05 ; Attribute length: 20 octets (5*4)
4841
00 00 ; (reserved)
4842
01 23 45 67 ; NONCE_S value
4843
89 ab cd ef
4844
fe dc ba 98
4845
76 54 32 10
4846
85 ; Attribute type: AT_NEXT_REAUTH_ID
4847
16 ; Attribute length: 88 octets (22*4)
4848
00 51 ; Actual re-auth identity length: 81 octets
4849
75 74 61 30 4d 30 69 79 49 73 4d 77 57 70 35 54
4850
54 64 53 64 6e 4f 4c 76 67 32 58 44 56 66 32 31
4851
4f 59 74 31 76 6e 66 69 4d 63 73 35 64 6e 49 44
4852
48 4f 49 46 56 61 76 49 52 7a 4d 52 79 7a 57 36
4853
76 46 7a 64 48 57 40 65 61 70 73 69 6d 2e 66 6f
4854
6f
4855
00 00 00 ; (attribute padding)
4856
4857
4858
4859
4860
4861
4862
4863
4864
4865
4866
4867
4868
4869
4870
4871
4872
4873
4874
Haverinen & Salowey Informational [Page 87]
4875
4876
RFC 4186 EAP-SIM Authentication January 2006
4877
4878
4879
The EAP packet looks like this:
4880
4881
01 ; Code: Request
4882
01 ; Identifier: 1
4883
00 a4 ; Length: 164 octets
4884
12 ; Type: EAP-SIM
4885
0d ; EAP-SIM subtype: Re-authentication
4886
00 00 ; (reserved)
4887
81 ; Attribute type: AT_IV
4888
05 ; Attribute length: 20 octets (5*4)
4889
00 00 ; (reserved)
4890
d5 85 ac 77 ; IV value
4891
86 b9 03 36
4892
65 7c 77 b4
4893
65 75 b9 c4
4894
82 ; Attribute type: AT_ENCR_DATA
4895
1d ; Attribute length: 116 octets (29*4)
4896
00 00 ; (reserved)
4897
68 62 91 a9 d2 ab c5 8c aa 32 94 b6 e8 5b 44 84
4898
6c 44 e5 dc b2 de 8b 9e 80 d6 9d 49 85 8a 5d b8
4899
4c dc 1c 9b c9 5c 01 b9 6b 6e ca 31 34 74 ae a6
4900
d3 14 16 e1 9d aa 9d f7 0f 05 00 88 41 ca 80 14
4901
96 4d 3b 30 a4 9b cf 43 e4 d3 f1 8e 86 29 5a 4a
4902
2b 38 d9 6c 97 05 c2 bb b0 5c 4a ac e9 7d 5e af
4903
f5 64 04 6c 8b d3 0b c3 9b e5 e1 7a ce 2b 10 a6
4904
0b ; Attribute type: AT_MAC
4905
05 ; Attribute length: 20 octets (5*4)
4906
00 00 ; (reserved)
4907
48 3a 17 99 ; MAC value
4908
b8 3d 7c d3
4909
d0 a1 e4 01
4910
d9 ee 47 70
4911
4912
The MAC is calculated over the EAP packet above (with MAC value set
4913
to zero; a total of 164 bytes).
4914
4915
Finally, the server derives new keys. The XKEY' is calculated as
4916
described in Section 7*:
4917
4918
XKEY' = 863dc120 32e08343 c1a2308d b48377f6 801f58d4
4919
4920
4921
4922
4923
4924
4925
4926
4927
4928
4929
4930
Haverinen & Salowey Informational [Page 88]
4931
4932
RFC 4186 EAP-SIM Authentication January 2006
4933
4934
4935
The new MSK and EMSK are derived using the PRNG (note that K_encr and
4936
K_aut stay the same).
4937
4938
MSK = 6263f614 973895e1 335f7e30 cff028ee
4939
2176f519 002c9abe 732fe0ef 00cf167c
4940
756d9e4c ed6d5ed6 40eb3fe3 8565ca07
4941
6e7fb8a8 17cfe8d9 adbce441 d47c4f5e
4942
EMSK = 3d8ff786 3a630b2b 06e2cf20 9684c13f
4943
6b82f992 f2b06f1b 54bf51ef 237f2a40
4944
1ef5e0d7 e098a34c 533eaebf 34578854
4945
b7721526 20a777f0 e0340884 a294fb73
4946
4947
A.10. EAP-Response/SIM/Re-authentication
4948
4949
The client's response includes the counter as well. The following
4950
plaintext will be encrypted and stored in the AT_ENCR_DATA attribute:
4951
4952
13 ; Attribute type: AT_COUNTER
4953
01 ; Attribute length: 4 octets (1*4)
4954
00 01 ; Counter value
4955
06 ; Attribute type: AT_PADDING
4956
03 ; Attribute length: 12 octets (3*4)
4957
00 00 00 00
4958
00 00 00 00
4959
00 00
4960
4961
The EAP packet looks like this:
4962
4963
02 ; Code: Response
4964
01 ; Identifier: 1
4965
00 44 ; Length: 68 octets
4966
12 ; Type: EAP-SIM
4967
0d ; EAP-SIM subtype: Re-authentication
4968
00 00 ; (reserved)
4969
81 ; Attribute type: AT_IV
4970
05 ; Attribute length: 20 octets (5*4)
4971
00 00 ; (reserved)
4972
cd f7 ff a6 ; IV value
4973
5d e0 4c 02
4974
6b 56 c8 6b
4975
76 b1 02 ea
4976
82 ; Attribute type: AT_ENCR_DATA
4977
05 ; Attribute length: 20 octets (5*4)
4978
00 00 ; (reserved)
4979
b6 ed d3 82
4980
79 e2 a1 42
4981
3c 1a fc 5c
4982
45 5c 7d 56
4983
4984
4985
4986
Haverinen & Salowey Informational [Page 89]
4987
4988
RFC 4186 EAP-SIM Authentication January 2006
4989
4990
4991
0b ; Attribute type: AT_MAC
4992
05 ; Attribute length: 20 octets (5*4)
4993
00 00 ; (reserved)
4994
fa f7 6b 71 ; MAC value
4995
fb e2 d2 55
4996
b9 6a 35 66
4997
c9 15 c6 17
4998
4999
The MAC is calculated over the EAP packet above (with MAC value set
5000
to zero), followed by the NONCE_S value (a total of 84 bytes).
5001
5002
The next packet will be EAP-Success:
5003
5004
03 ; Code: Success
5005
01 ; Identifier: 1
5006
00 04 ; Length: 4 octets
5007
5008
Appendix B. Pseudo-Random Number Generator
5009
5010
The "|" character denotes concatenation, and "^" denotes
5011
exponentiation.
5012
5013
Step 1: Choose a new, secret value for the seed-key, XKEY
5014
5015
Step 2: In hexadecimal notation let
5016
t = 67452301 EFCDAB89 98BADCFE 10325476 C3D2E1F0
5017
This is the initial value for H0|H1|H2|H3|H4
5018
in the FIPS SHS [SHA-1]
5019
5020
Step 3: For j = 0 to m - 1 do
5021
3.1 XSEED_j = 0 /* no optional user input */
5022
3.2 For i = 0 to 1 do
5023
a. XVAL = (XKEY + XSEED_j) mod 2^b
5024
b. w_i = G(t, XVAL)
5025
c. XKEY = (1 + XKEY + w_i) mod 2^b
5026
3.3 x_j = w_0|w_1
5027
5028
5029
5030
5031
5032
5033
5034
5035
5036
5037
5038
5039
5040
5041
5042
Haverinen & Salowey Informational [Page 90]
5043
5044
RFC 4186 EAP-SIM Authentication January 2006
5045
5046
5047
Authors' Addresses
5048
5049
Henry Haverinen (editor)
5050
Nokia Enterprise Solutions
5051
P.O. Box 12
5052
FIN-40101 Jyvaskyla
5053
Finland
5054
5055
EMail: henry.haverinen@nokia.com
5056
5057
5058
Joseph Salowey (editor)
5059
Cisco Systems
5060
2901 Third Avenue
5061
Seattle, WA 98121
5062
USA
5063
5064
Phone: +1 206 256 3380
5065
EMail: jsalowey@cisco.com
5066
5067
5068
5069
5070
5071
5072
5073
5074
5075
5076
5077
5078
5079
5080
5081
5082
5083
5084
5085
5086
5087
5088
5089
5090
5091
5092
5093
5094
5095
5096
5097
5098
Haverinen & Salowey Informational [Page 91]
5099
5100
RFC 4186 EAP-SIM Authentication January 2006
5101
5102
5103
Full Copyright Statement
5104
5105
Copyright (C) The Internet Society (2006).
5106
5107
This document is subject to the rights, licenses and restrictions
5108
contained in BCP 78, and except as set forth therein, the authors
5109
retain all their rights.
5110
5111
This document and the information contained herein are provided on an
5112
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
5113
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
5114
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
5115
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
5116
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
5117
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
5118
5119
Intellectual Property
5120
5121
The IETF takes no position regarding the validity or scope of any
5122
Intellectual Property Rights or other rights that might be claimed to
5123
pertain to the implementation or use of the technology described in
5124
this document or the extent to which any license under such rights
5125
might or might not be available; nor does it represent that it has
5126
made any independent effort to identify any such rights. Information
5127
on the procedures with respect to rights in RFC documents can be
5128
found in BCP 78 and BCP 79.
5129
5130
Copies of IPR disclosures made to the IETF Secretariat and any
5131
assurances of licenses to be made available, or the result of an
5132
attempt made to obtain a general license or permission for the use of
5133
such proprietary rights by implementers or users of this
5134
specification can be obtained from the IETF on-line IPR repository at
5135
http://www.ietf.org/ipr.
5136
5137
The IETF invites any interested party to bring to its attention any
5138
copyrights, patents or patent applications, or other proprietary
5139
rights that may cover technology that may be required to implement
5140
this standard. Please address the information to the IETF at
5141
ietf-ipr@ietf.org.
5142
5143
Acknowledgement
5144
5145
Funding for the RFC Editor function is provided by the IETF
5146
Administrative Support Activity (IASA).
5147
5148
5149
5150
5151
5152
5153
5154
Haverinen & Salowey Informational [Page 92]
5155
Loggerhead is a web-based interface for Breezy
Version: 2.0.1