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@item Certificate authentication
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@item Anonymous authentication
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@item @acronym{SRP} authentication
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@item @acronym{PSK} authentication
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@item Certificate authentication: Authenticated key exchange using public key infrastructure and certificates (X.509 or OpenPGP).
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@item @acronym{SRP} authentication: Authenticated key exchange using a password.
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@item @acronym{PSK} authentication: Authenticated key exchange using a pre-shared key.
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@item Anonymous authentication: Key exchange without peer authentication.
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@section Certificate authentication
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@subsection Authentication using @acronym{X.509} certificates
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@cindex @acronym{X.509} certificates
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@cindex X.509 certificates
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@acronym{X.509} certificates contain the public parameters, of a
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public key algorithm, and an authority's signature, which proves the
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@showfuncdesc{gnutls_certificate_set_verify_function}
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Note that the DHE key exchange methods are generally
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slower@footnote{It really depends on the group used. Primes with
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slower@footnote{It depends on the group used. Primes with
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lesser bits are always faster, but also easier to break. See @ref{Selecting cryptographic key sizes}
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for the acceptable security levels.}
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and require Diffie-Hellman parameters to be generated and associated with a credentials
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structure, by the server (see @ref{Parameter generation}).
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for the acceptable security levels.} than the elliptic curves counterpart
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(ECDHE). Moreover the plain Diffie-Hellman key exchange
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requires parameters to be generated and associated with a credentials
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structure by the server (see @ref{Parameter generation}).
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@float Table,tab:key-exchange
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@multitable @columnfractions .2 .7
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@node Authentication using SRP
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@section Authentication using @acronym{SRP}
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@cindex @acronym{SRP} authentication
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@cindex SRP authentication
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Authentication via the Secure Remote Password protocol,
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@acronym{SRP} (see @xcite{RFC2945} for a description of SRP),
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is supported. The @acronym{SRP} key exchange is an extension to the
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@acronym{TLS} protocol, and it is a password based authentication
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(unlike @acronym{X.509} or @acronym{OpenPGP} that use certificates).
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The two peers can be identified using a single password, or there can
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be combinations where the client is authenticated using @acronym{SRP}
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@acronym{GnuTLS} supported authentication via the Secure Remote Password
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or @acronym{SRP} protocol (see @xcite{RFC2945,TOMSRP} for a description).
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The @acronym{SRP} key exchange is an extension to the
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@acronym{TLS} protocol, and it provided an authenticated with a
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password key exchange. The peers can be identified using a single password,
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or there can be combinations where the client is authenticated using @acronym{SRP}
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and the server using a certificate.
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The advantage of @acronym{SRP} authentication, over other proposed
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secure password authentication schemes, is that @acronym{SRP} does not
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require the server to hold the user's password. This kind of
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protection is similar to the one used traditionally in the @acronym{UNIX}
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secure password authentication schemes, is that @acronym{SRP} is not
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susceptible to off-line dictionary attacks.
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Moreover, SRP does not require the server to hold the user's password.
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This kind of protection is similar to the one used traditionally in the @acronym{UNIX}
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@file{/etc/passwd} file, where the contents of this file did not cause
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harm to the system security if they were revealed. The @acronym{SRP}
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needs instead of the plain password something called a verifier, which
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is calculated using the user's password, and if stolen cannot be used
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to impersonate the user. Check @xcite{TOMSRP} for a detailed
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description of the @acronym{SRP} protocol and the Stanford
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@acronym{SRP} libraries, which includes a PAM module that synchronizes
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to impersonate the user.
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The Stanford @acronym{SRP} libraries, include a PAM module that synchronizes
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the system's users passwords with the @acronym{SRP} password
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files. That way @acronym{SRP} authentication could be used for all the
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files. That way @acronym{SRP} authentication could be used for all users
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The implementation in @acronym{GnuTLS} is based on @xcite{TLSSRP} and
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the supported @acronym{SRP} key exchange methods are:
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The implementation in @acronym{GnuTLS} is based on @xcite{TLSSRP}. The
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supported key exchange methods are shown below.
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@showfuncC{gnutls_psk_set_server_credentials_function,gnutls_psk_set_server_credentials_hint,gnutls_psk_client_get_hint}
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Helper functions are included in @acronym{GnuTLS}, and may be used to generate and
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maintain @acronym{PSK} keys.
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@showfuncdesc{gnutls_hex_encode}
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@showfuncdesc{gnutls_hex_decode}
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Helper functions to generate and maintain @acronym{PSK} keys are also included
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@showfuncC{gnutls_key_generate,gnutls_hex_encode,gnutls_hex_decode}
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@node Authentication and credentials
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doc/cha-auth.texi
