Subject: Re: SRP and SM2

From: Keith Burdis <[email-masked]>
Date: Sun, 22 Apr 2001 23:15:36 +0200

On Mon 2001-03-26 (17:20), Chris Newman wrote:
> I think SRP fills a useful niche.  Relative to DIGEST-MD5, it trades speed 
> and management flexability for a significant improvement in wire and 
> server-side security.

What management flexibility tradeoffs are there in using SRP over
DIGEST-MD5?
 
> However, Jeff Schiller has made it quite clear that slow PK-based 
> algorithms (like SRP) need a fast restart mechanism before they're suitable 
> for the standards track.  If I understand the proposal correct, SM2 is the 
> fast-restart mechanism to go with SRP and thus SM2 needs to go to the 
> standards track before or at the same time that SRP does.  If we only look 
> at one of the two in the WG, it needs to be SM2 since that could have a 
> broader scope than just SRP.

You are correct. The slowest part of the SRP exchange is the generation of
the ephemeral keypairs by the client and the server. Using SRP with SM2
eliminates the need for new keypairs to be generated when a session is
reused, which leads to large speed improvements. I agree that a way to reuse
SRP sessions is definitely necessary before SRP can progress further.

SM2 is generally useful as a means of reusing sessions for any SASL
mechanism. However if it is not available as a standards track document then
something similar will have to be added to the SRP specification. The
downside of this is that we will have a different way of doing session reuse
for DIGEST-MD5 and SRP, and any new mechanisms will also have to specify a
means of reusing their sessions.

One possibility is to add SM2 to RFC 2222, but I doubt that anyone will like
that idea :-)

As noted in section 7.4 of the SM2 draft, the "subsequent authentication"
described in RFC 2831 maps nicely on to the SM2 exchange.  I suggest
removing section 2.2 of RFC 2831 in favour of SM2.

Comments?

> 		- Chris

 - Keith
--
Keith Burdis - MSc (Computer Science) - Rhodes University, South Africa
IRC: Panthras					JAPH 	QEFH
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From: Keith Burdis <[email-masked]>
Date: Sun, 22 Apr 2001 23:15:36 +0200

Comments?

 - Keith