[Cfrg] On the topic of the SPAKE2 draft

Paul Lambert <paul@marvell.com> Fri, 23 January 2015 21:44 UTC

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From: Paul Lambert <paul@marvell.com>
To: "cfrg@irtf.org" <cfrg@irtf.org>
Date: Fri, 23 Jan 2015 13:44:00 -0800
Thread-Topic: On the topic of the SPAKE2 draft
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Subject: [Cfrg] On the topic of the SPAKE2 draft
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The draft-irtf-cfrg-spake2-00.txt text says:

   Both A and B calculate a group element K. A calculates it as x(S-wN),
   while B calculates it as y(T-wM). A knows S because it has received
   it, and likewise B knows T.

How does A know to use N and B to use M?

The protocol is not symmetric and the different values define different roles in the protocol.

What happens if both sides pick the same value?

Can the protocol specification be made symmetric ...

Also in the draft:

   Note that
   the choice of M and N is critical: anyone who is aware of an x such
   that xN=M, or xG=N or M can break the scheme above.

By 'anyone', does that include party A in its choice of N?
If A picked x and knew that xG=N is it still a issue?