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IPSECKEY WG M. Richardson
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A method for storing IPsec keying material in DNS.
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draft-ietf-ipseckey-rr-07.txt
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This document is an Internet-Draft and is in full conformance with
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all provisions of Section 10 of RFC2026.
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Internet-Drafts are working documents of the Internet Engineering
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Task Force (IETF), its areas, and its working groups. Note that
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other groups may also distribute working documents as Internet-
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Internet-Drafts are draft documents valid for a maximum of six months
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and may be updated, replaced, or obsoleted by other documents at any
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time. It is inappropriate to use Internet-Drafts as reference
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material or to cite them other than as "work in progress."
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The list of current Internet-Drafts can be accessed at http://
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www.ietf.org/ietf/1id-abstracts.txt.
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The list of Internet-Draft Shadow Directories can be accessed at
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http://www.ietf.org/shadow.html.
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This Internet-Draft will expire on March 4, 2004.
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Copyright (C) The Internet Society (2003). All Rights Reserved.
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This document describes a new resource record for DNS. This record
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may be used to store public keys for use in IPsec systems.
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This record replaces the functionality of the sub-type #1 of the KEY
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Resource Record, which has been obsoleted by RFC3445.
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1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
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1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
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1.2 Usage Criteria . . . . . . . . . . . . . . . . . . . . . . . . 3
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2. Storage formats . . . . . . . . . . . . . . . . . . . . . . . 4
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2.1 IPSECKEY RDATA format . . . . . . . . . . . . . . . . . . . . 4
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2.2 RDATA format - precedence . . . . . . . . . . . . . . . . . . 4
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2.3 RDATA format - algorithm type . . . . . . . . . . . . . . . . 4
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2.4 RDATA format - gateway type . . . . . . . . . . . . . . . . . 4
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2.5 RDATA format - gateway . . . . . . . . . . . . . . . . . . . . 5
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2.6 RDATA format - public keys . . . . . . . . . . . . . . . . . . 5
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3. Presentation formats . . . . . . . . . . . . . . . . . . . . . 7
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3.1 Representation of IPSECKEY RRs . . . . . . . . . . . . . . . . 7
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3.2 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
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4. Security Considerations . . . . . . . . . . . . . . . . . . . 9
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4.1 Active attacks against unsecured IPSECKEY resource records . . 9
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5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
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6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
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Normative references . . . . . . . . . . . . . . . . . . . . . 13
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Non-normative references . . . . . . . . . . . . . . . . . . . 14
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Author's Address . . . . . . . . . . . . . . . . . . . . . . . 14
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Full Copyright Statement . . . . . . . . . . . . . . . . . . . 15
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The type number for the IPSECKEY RR is TBD.
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The IPSECKEY resource record (RR) is used to publish a public key
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that is to be associated with a Domain Name System (DNS) name for use
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with the IPsec protocol suite. This can be the public key of a
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host, network, or application (in the case of per-port keying).
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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 [8].
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An IPSECKEY resource record SHOULD be used in combination with DNSSEC
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unless some other means of authenticating the IPSECKEY resource
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It is expected that there will often be multiple IPSECKEY resource
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records at the same name. This will be due to the presence of
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multiple gateways and the need to rollover keys.
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This resource record is class independent.
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2.1 IPSECKEY RDATA format
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The RDATA for an IPSECKEY RR consists of a precedence value, a public
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key, algorithm type, and an optional gateway address.
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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
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| precedence | gateway type | algorithm | gateway |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-------------+ +
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
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2.2 RDATA format - precedence
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This is an 8-bit precedence for this record. This is interpreted in
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the same way as the PREFERENCE field described in section 3.3.9 of
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Gateways listed in IPSECKEY records with lower precedence are to be
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attempted first. Where there is a tie in precedence, the order
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should be non-deterministic.
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2.3 RDATA format - algorithm type
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The algorithm type field identifies the public key's cryptographic
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algorithm and determines the format of the public key field.
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A value of 0 indicates that no key is present.
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The following values are defined:
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1 A DSA key is present, in the format defined in RFC2536 [11]
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2 A RSA key is present, in the format defined in RFC3110 [12]
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2.4 RDATA format - gateway type
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The gateway type field indicates the format of the information that
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is stored in the gateway field.
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The following values are defined:
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0 No gateway is present
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1 A 4-byte IPv4 address is present
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2 A 16-byte IPv6 address is present
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3 A wire-encoded domain name is present. The wire-encoded format is
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self-describing, so the length is implicit. The domain name MUST
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2.5 RDATA format - gateway
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The gateway field indicates a gateway to which an IPsec tunnel may be
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created in order to reach the entity named by this resource record.
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There are three formats:
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A 32-bit IPv4 address is present in the gateway field. The data
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portion is an IPv4 address as described in section 3.4.1 of RFC1035
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[2]. This is a 32-bit number in network byte order.
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A 128-bit IPv6 address is present in the gateway field. The data
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portion is an IPv6 address as described in section 2.2 of RFC1886
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[7]. This is a 128-bit number in network byte order.
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The gateway field is a normal wire-encoded domain name, as described
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in section 3.3 of RFC1035 [2]. Compression MUST NOT be used.
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2.6 RDATA format - public keys
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Both of the public key types defined in this document (RSA and DSA)
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inherit their public key formats from the corresponding KEY RR
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formats. Specifically, the public key field contains the algorithm-
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specific portion of the KEY RR RDATA, which is all of the KEY RR DATA
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after the first four octets. This is the same portion of the KEY RR
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that must be specified by documents that define a DNSSEC algorithm.
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Those documents also specify a message digest to be used for
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generation of SIG RRs; that specification is not relevant for
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Future algorithms, if they are to be used by both DNSSEC (in the KEY
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RR) and IPSECKEY, are likely to use the same public key encodings in
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both records. Unless otherwise specified, the IPSECKEY public key
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field will contain the algorithm-specific portion of the KEY RR RDATA
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for the corresponding algorithm. The algorithm must still be
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designated for use by IPSECKEY, and an IPSECKEY algorithm type number
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(which might be different than the DNSSEC algorithm number) must be
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The DSA key format is defined in RFC2536 [11]
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The RSA key format is defined in RFC3110 [12], with the following
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The earlier definition of RSA/MD5 in RFC2065 limited the exponent and
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modulus to 2552 bits in length. RFC3110 extended that limit to 4096
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bits for RSA/SHA1 keys. The IPSECKEY RR imposes no length limit on
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RSA public keys, other than the 65535 octet limit imposed by the two-
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octet length encoding. This length extension is applicable only to
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IPSECKEY and not to KEY RRs.
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3. Presentation formats
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3.1 Representation of IPSECKEY RRs
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IPSECKEY RRs may appear in a zone data master file. The precedence,
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gateway type and algorithm and gateway fields are REQUIRED. The
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base64 encoded public key block is OPTIONAL; if not present, then the
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public key field of the resource record MUST be construed as being
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zero octets in length.
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The algorithm field is an unsigned integer. No mnemonics are
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If no gateway is to be indicated, then the gateway type field MUST be
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zero, and the gateway field MUST be "."
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The Public Key field is represented as a Base64 encoding of the
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Public Key. Whitespace is allowed within the Base64 text. For a
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definition of Base64 encoding, see RFC1521 [3] Section 5.2.
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The general presentation for the record as as follows:
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IN IPSECKEY ( precedence gateway-type algorithm
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gateway base64-encoded-public-key )
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An example of a node 192.0.2.38 that will accept IPsec tunnels on its
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38.2.0.192.in-addr.arpa. 7200 IN IPSECKEY ( 10 1 2
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AQNRU3mG7TVTO2BkR47usntb102uFJtugbo6BSGvgqt4AQ== )
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An example of a node, 192.0.2.38 that has published its key only.
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38.2.0.192.in-addr.arpa. 7200 IN IPSECKEY ( 10 0 2
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AQNRU3mG7TVTO2BkR47usntb102uFJtugbo6BSGvgqt4AQ== )
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An example of a node, 192.0.2.38 that has delegated authority to the
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38.2.0.192.in-addr.arpa. 7200 IN IPSECKEY ( 10 1 2
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AQNRU3mG7TVTO2BkR47usntb102uFJtugbo6BSGvgqt4AQ== )
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An example of a node, 192.0.1.38 that has delegated authority to the
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node with the identity "mygateway.example.com".
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38.1.0.192.in-addr.arpa. 7200 IN IPSECKEY ( 10 3 2
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mygateway.example.com.
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AQNRU3mG7TVTO2BkR47usntb102uFJtugbo6BSGvgqt4AQ== )
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An example of a node, 2001:0DB8:0200:1:210:f3ff:fe03:4d0 that has
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delegated authority to the node 2001:0DB8:c000:0200:2::1
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$ORIGIN 1.0.0.0.0.0.2.8.B.D.0.1.0.0.2.ip6.int.
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0.d.4.0.3.0.e.f.f.f.3.f.0.1.2.0 7200 IN IPSECKEY ( 10 2 2
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2001:0DB8:0:8002::2000:1
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AQNRU3mG7TVTO2BkR47usntb102uFJtugbo6BSGvgqt4AQ== )
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4. Security Considerations
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This entire memo pertains to the provision of public keying material
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for use by key management protocols such as ISAKMP/IKE (RFC2407) [9].
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The IPSECKEY resource record contains information that SHOULD be
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communicated to the end client in an integral fashion - i.e. free
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from modification. The form of this channel is up to the consumer of
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the data - there must be a trust relationship between the end
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consumer of this resource record and the server. This relationship
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may be end-to-end DNSSEC validation, a TSIG or SIG(0) channel to
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another secure source, a secure local channel on the host, or some
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combination of the above.
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The keying material provided by the IPSECKEY resource record is not
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sensitive to passive attacks. The keying material may be freely
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disclosed to any party without any impact on the security properties
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of the resulting IPsec session: IPsec and IKE provide for defense
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against both active and passive attacks.
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Any user of this resource record MUST carefully document their trust
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model, and why the trust model of DNSSEC is appropriate, if that is
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the secure channel used.
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4.1 Active attacks against unsecured IPSECKEY resource records
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This section deals with active attacks against the DNS. These
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attacks require that DNS requests and responses be intercepted and
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changed. DNSSEC is designed to defend against attacks of this kind.
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The first kind of active attack is when the attacker replaces the
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keying material with either a key under its control or with garbage.
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If the attacker is not able to mount a subsequent man-in-the-middle
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attack on the IKE negotiation after replacing the public key, then
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this will result in a denial of service, as the authenticator used by
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If the attacker is able to both to mount active attacks against DNS
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and is also in a position to perform a man-in-the-middle attack on
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IKE and IPsec negotiations, then the attacker will be in a position
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to compromise the resulting IPsec channel. Note that an attacker
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must be able to perform active DNS attacks on both sides of the IKE
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negotiation in order for this to succeed.
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The second kind of active attack is one in which the attacker
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replaces the the gateway address to point to a node under the
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attacker's control. The attacker can then either replace the public
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key or remove it, thus providing an IPSECKEY record of its own to
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match the gateway address.
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This later form creates a simple man-in-the-middle since the attacker
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can then create a second tunnel to the real destination. Note that,
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as before, this requires that the attacker also mount an active
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attack against the responder.
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Note that the man-in-the-middle can not just forward cleartext
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packets to the original destination. While the destination may be
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willing to speak in the clear, replying to the original sender, the
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sender will have already created a policy expecting ciphertext.
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Thus, the attacker will need to intercept traffic from both sides.
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In some cases, the attacker may be able to accomplish the full
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intercept by use of Network Addresss/Port Translation (NAT/NAPT)
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Note that the danger here only applies to cases where the gateway
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field of the IPSECKEY RR indicates a different entity than the owner
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name of the IPSECKEY RR. In cases where the end-to-end integrity of
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the IPSECKEY RR is suspect, the end client MUST restrict its use of
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the IPSECKEY RR to cases where the RR owner name matches the content
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of the gateway field.
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5. IANA Considerations
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This document updates the IANA Registry for DNS Resource Record Types
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by assigning type X to the IPSECKEY record.
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This document creates an IANA registry for the algorithm type field.
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Values 0, 1 and 2 are defined in Section 2.3. Algorithm numbers 3
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through 255 can be assigned by IETF Consensus (see RFC2434 [6]).
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This document creates an IANA registry for the gateway type field.
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Values 0, 1, 2 and 3 are defined in Section 2.4. Algorithm numbers 4
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through 255 can be assigned by Standards Action (see RFC2434 [6]).
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My thanks to Paul Hoffman, Sam Weiler, Jean-Jacques Puig, Rob
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Austein, and Olafur Gurmundsson who reviewed this document carefully.
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Additional thanks to Olafur Gurmundsson for a reference
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[1] Mockapetris, P., "Domain names - concepts and facilities", STD
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13, RFC 1034, November 1987.
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[2] Mockapetris, P., "Domain names - implementation and
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specification", STD 13, RFC 1035, November 1987.
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[3] Borenstein, N. and N. Freed, "MIME (Multipurpose Internet Mail
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Extensions) Part One: Mechanisms for Specifying and Describing
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the Format of Internet Message Bodies", RFC 1521, September
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[4] Bradner, S., "The Internet Standards Process -- Revision 3", BCP
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9, RFC 2026, October 1996.
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[5] Eastlake, D. and C. Kaufman, "Domain Name System Security
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Extensions", RFC 2065, January 1997.
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[6] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
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Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
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Non-normative references
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[7] Thomson, S. and C. Huitema, "DNS Extensions to support IP
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version 6", RFC 1886, December 1995.
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[8] Bradner, S., "Key words for use in RFCs to Indicate Requirement
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Levels", BCP 14, RFC 2119, March 1997.
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[9] Piper, D., "The Internet IP Security Domain of Interpretation
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for ISAKMP", RFC 2407, November 1998.
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[10] Eastlake, D., "Domain Name System Security Extensions", RFC
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[11] Eastlake, D., "DSA KEYs and SIGs in the Domain Name System
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(DNS)", RFC 2536, March 1999.
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[12] Eastlake, D., "RSA/SHA-1 SIGs and RSA KEYs in the Domain Name
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System (DNS)", RFC 3110, May 2001.
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[13] Massey, D. and S. Rose, "Limiting the Scope of the KEY Resource
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Record (RR)", RFC 3445, December 2002.
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Michael C. Richardson
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Sandelman Software Works
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EMail: mcr@sandelman.ottawa.on.ca
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URI: http://www.sandelman.ottawa.on.ca/
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Full Copyright Statement
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Copyright (C) The Internet Society (2003). All Rights Reserved.
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This document and translations of it may be copied and furnished to
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others, and derivative works that comment on or otherwise explain it
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or assist in its implementation may be prepared, copied, published
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and distributed, in whole or in part, without restriction of any
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kind, provided that the above copyright notice and this paragraph are
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included on all such copies and derivative works. However, this
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document itself may not be modified in any way, such as by removing
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the copyright notice or references to the Internet Society or other
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Internet organizations, except as needed for the purpose of
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developing Internet standards in which case the procedures for
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copyrights defined in the Internet Standards process must be
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followed, or as required to translate it into languages other than
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The limited permissions granted above are perpetual and will not be
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revoked by the Internet Society or its successors or assigns.
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This document and the information contained herein is provided on an
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"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
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TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
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HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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Funding for the RFC Editor function is currently provided by the
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