Re: Optional domain/realm for SCRAM? (Re: Crypto agility in SCRAM + draft-josefsson-password-auth?)

[Nicolas Williams <Nicolas.Williams@xxxxxxx>]

On Tue, Mar 18, 2008 at 04:52:49PM +0100, Simon Josefsson wrote:
> Nicolas Williams <Nicolas.Williams@xxxxxxx> writes:
> > Not being able to enroll once but authenticate to many servers seems
> > obnoxious.
> 
> I think this is out of scope for a simple password based password
> mechanism.
> 
> If you have an infrastructure like the one you describe, either Kerberos
> (if you prefer symmetric encryption) or TLS+EXTERNAL (if you prefer
> asymmetric encryption) seems like a better approach to me.

Hmmm, I think I can live with this answer, but I also think that a SCRAM
with this option will have sufficiently different properties from
Kerberos that in many case it could be preferable (specifically: no
online infrastructure requirement for the client).

> If you really want to achieve something like you want, wouldn't the
> following work?  Enroll the user once, and then ask the user to use a
> username like 'user@xxxxxxxxxxxxx', 'user@xxxxxxxxxxxxx' for each of the
> servers in that realm.  The enrollment process could push out the
> password-equivalent hash to each server.

Ick.

> In my experience, the realms feature was not used widely with
> DIGEST-MD5, but made the specification more complex.

OK, I withdraw this proposal.