Re: Adding a PRF to GSSAPI V3

Sam Hartman wrote:
> 
> Hi.  Larry, Niico and I would support the idea of adding some sort of
> PRF to the  GSSAPI.  
> 
> The intent of this would be that you have gss_prf that takes a context
> and some goop as input and returns some psuedo-random goop as output.
> The output would be constant for a given context and given input goop.
> This would presumably be a optional feature of GSSAPI.

You mean cryptographically strong pseudo-random goop as output --
similar to SSL/TLS deriving session-keys from a shared master secret?

That might be useful for those who want to use gssapi for authenication
but do the actual crypto on their own.

Having this as an optional extension should be OK.

There may be technical and policital reasons why one mechanism
or another will not adopt this functionality.
 
The political reasons may be that a gssapi mechanism should be
authentication only or authentication plus integrity but no confidentiality
(this was how DCE implemented the former US crypto export regulations).
Providing cryptographically strong shared secrets to the communication
peers of an established security context was incompatible with
that regulation.

Technical reasons may be that the gssapi mechanism provides authentication
only and no means to establish a cryptographically strong shared secret
between the communication peers during authentication which could be
used as a master secret.  Simple challenge-response schemes such
as Microsoft's NTLM authentication come to mind.  Or authentication
based on DSA-certificates.

-Martin
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