Re: [SPKM] Re: [TLS] DTLS and GSS-API

>>>>> "Martin" == Martin Rex <martin.rex@sap.com> writes:
    >> 
    >> An alternate proposal for solving this problem was discussed in
    >> the past: construct a GSS-API mechanism based on DTLS.
    >> Advantages of this solution include reuse of code and
    >> specification between GSS-API and TLS implementations.  When
    >> new ciphers are specified for TLS they would be available for
    >> NFS.  We would not need to keep updating a GSS mechanism as
    >> public-key algorithms evolve and problems are found.
    >> 
    >> There are two main drawbacks I've heard to the DTLS proposal.
    >> First, we don't have a draft.  Second, it would not be
    >> interoperable with SPKM-3 deployments.

    Martin> There is a substantial difference between GSS-API and TLS
    Martin> which should not be ignored: In the GSS-API architecture,
    Martin> context level tokens (which exchange cryptographic
    Martin> material and perform the authentication) can only be
    Martin> exchanged at the beginning.

    Martin> After a security context has been established, the message
    Martin> flow depends entirely on the communication characteristics
    Martin> of the application, and may be entirey uni-directional and
    Martin> may preclude even alien attempts of a gssapi mechanism to
    Martin> piggy-back context-token on protected message tokens.

    Martin> With TLS, on the other hand, each of the communication
    Martin> peers may request a renegotiation of context parameters at
    Martin> (almost) any time during the communication.

I talked to Eric about this in another context.  He claimed that as a
practical matter it does not work if animplementation does a new
handshake without the cooperation of the upper-layer application.  You
are correct though that a DTLS GSS-API mechanism could only be
specified on the standards track if this issue were dealt with in some
manner that preserved the GSS-API model.

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