AFS and tokenforwarding

[Nicolas Williams]

On Thu, Oct 04, 2001 at 09:43:29PM +0200, Bjoern Groenvall wrote:
> >>>>> "Nicolas" == Nicolas Williams <Nicolas.Williams at ubsw.com> writes:
> 
> Nicolas> I was thinking that AFS token passing would be mixed with
> Nicolas> Kerberos network authentication. If it's Kerberos V then I'd
> Nicolas> expect mutual auth to be used.
> 
> Yes, kerberos mutual authentication is used, however it is used the
> wrong way. A masquerading server can use the real server as an
> oracle. Thus mutual authentication is used, but it does not really
> provide any mutual authentication.

??? How? In Kerberos V I don't see how.

> Nicolas> Then again, I've ever used SSHv1 with Kerberos -- only SSHv2
> Nicolas> with GSS/Kerberos (thanks to Simon Wilkinson's patches) and
> Nicolas> SSH w/ GSS *does* require mutual authentication.
> 
> Hopefully this is done right in v2, I don't enough about v2 though.
> 
> Nicolas> So how will you make AFS token passing in SSHv2?
> 
> I don't really now enough about the details of v2 authentication and
> session key generation. In theory, it should be possible to pass the
> token (encrypted) along with the authentication information in such a
> format so that only a legitimate server can unpack the token. If this
> matches the v2 model, I simply don't know.

There's two competing SSH/GSS proposals. The better one (IMHO) is
implemented by patches posted here (*). GSS-API is used, which means,
for Kerberos, that the AP_REQ and KRB_CREDS are sent together on the
first token, but the KRB_CREDS are sent doubly encrypted in the
authenticator checksum field (a gross network optimization hack --
sigh). The patches I'm referring to require mutual authentication.
Session key generation can be done in either of two ways: GSS-protected
Diffie-Hellman exchange (which eschews the SSH host keys) or SSHv2 host
key based session key generation and SSH-protected GSS exchange.

(*) http://www.sxw.org.uk/computing/patches/

> Cheers,
> Björn
> 

Cheers,

Nico
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