Subject: [Cfrg] I-D Action: draft-irtf-cfrg-spake2-06.txt

From: [email-masked]
Date: Wed, 15 Aug 2018 08:39:56 -0700

A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Crypto Forum RG of the IRTF.

        Title           : SPAKE2, a PAKE
        Authors         : Watson Ladd
                          Benjamin Kaduk
	Filename        : draft-irtf-cfrg-spake2-06.txt
	Pages           : 9
	Date            : 2018-08-15

Abstract:
   This document describes SPAKE2, a means for two parties that share a
   password to derive a strong shared key with no risk of disclosing the
   password.  This method is compatible with any group, is
   computationally efficient, and has a strong security proof.

The IETF datatracker status page for this draft is:
https://datatracker.ietf.org/doc/draft-irtf-cfrg-spake2/

There are also htmlized versions available at:
https://tools.ietf.org/html/draft-irtf-cfrg-spake2-06
https://datatracker.ietf.org/doc/html/draft-irtf-cfrg-spake2-06

A diff from the previous version is available at:
https://www.ietf.org/rfcdiff?url2=draft-irtf-cfrg-spake2-06

Please note that it may take a couple of minutes from the time of submission
until the htmlized version and diff are available at tools.ietf.org.

Internet-Drafts are also available by anonymous FTP at:
ftp://ftp.ietf.org/internet-drafts/

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From: Benjamin Kaduk <[email-masked]>
Date: Wed, 15 Aug 2018 10:44:02 -0500

This is almost a no-change rev to bump the expiration, but I did add a
little note about the SPAKE2+ proof status, in light of what I could
divulge from Hugo's slides from Montreal.  (I had a schedule conflict and
couldn't attend in person.)

I don't know of any other outstanding issues, so from my point of view this
one seems ready for RGLC -- we have a consumer in the wild already for
Kerberos, and some interest from other areas as well.

-Ben

On Wed, Aug 15, 2018 at 08:39:56AM -0700, [email-masked] wrote:
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From: Hugo Krawczyk <[email-masked]>
Date: Wed, 15 Aug 2018 13:35:18 -0400

Just to clarify the status of proofs for SPAKE2 and SPAKE2+ (as I said in
my still-unofficial OPAQUE draft and in the presentation in Montreal):

SPAKE2 has a proof of security as a PAKE in [REF], as you say. (Though I
don't know what you mean by "strong proof")

SPAKE2+ was described in [TDH] as an asymmetric/augmented PAKE without a
proof of security (or even a model), just an informal rationale for the
protocol design. I checked with the authors of [TDH] and they don't claim
to have a proof (written or unwritten). I am not implying that the protocol
is insecure. Lacking a proof I don't know - this is one of the trickiest
areas of key exchange. What we know for sure is that the protocol is not
secure against pre-computation attacks. The sentence  "SPAKE2+ appears in
[TDH], along with a security proof"  needs to be revised accordingly.

If you think any of the above is inaccurate please let me know.

Hugo

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From: Benjamin Kaduk <[email-masked]>
Date: Wed, 15 Aug 2018 12:39:57 -0500

Hi Hugo,

Thanks for clarifying. <inline>

> don't know what you mean by "strong proof")

I think I inherited that text -- I don't know what "strong" means there,
either.

> If you think any of the above is inaccurate please let me know.

I don't think I have access to [TDH], so I'll have to take your word for
it.  But, it does sound like the text should be revised, given the above.
(I'll wait a couple days to see if there's further discussion before
submitting a new rev.)

-Ben

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From: Hugo Krawczyk <[email-masked]>
Date: Wed, 15 Aug 2018 14:09:35 -0400

[tdh] https://eprint.iacr.org/2008/067
Section 9.