Subject: [Cfrg] Dragonfly/RFC 7664 clarification

From: "Paterson, Kenny" <[email-masked]>
Date: Wed, 18 Nov 2015 12:57:18 +0000

Dear CFRG,

There has been some discussion on the list about changes made to RFC 7664
(Dragonfly Key Exchange) at a late stage in the publication process. The
chairs would like to add some clarity here.

Late in the process, one of us (Kenny) noticed that a paper was due to
appear at a conference, ISC 2015, which offered a security proof for a
protocol close to Dragonfly. We were able to obtain a pre-publication
version of the paper from the authors, Lancreon and Skrobot, and make it
available to Dan Harkins, the author of RFC 7664. We agreed with Dan that
the RFC should make reference to this paper if possible. It now does so,
as [lanskro].

However, the paper [lanskro] does not analyse Dragonfly as specified in
RFC 7664, but a variant of it in which the identities are hashed as part
of the final key derivation process. The chairs had two choices at this
point:

- Ask the author (Dan) to change the protocol in the RFC to include
identifiers, and cite [lanskro].

- Ask the author to include a reference to [lanskro] and make a careful
statement about what the proof in that paper says about the Dragonfly
protocol as specified in the RFC.

Given that the group had extensively reviewed Dragonfly as specified, we
decided that the second option here was the better one to take. The exact
wording in the RFC is as follows:

"[lanskro] provides a security proof of Dragonfly in the random oracle
   model when both identities are included in the data sent in the
   Confirm Exchange (see Section 3.4)."

Secondary factors in forming the chairs' decision included the fact that
the original intention of the work was to produce a public specification
of a protocol in use in other standards and the fact that there is IPR on
the idea of hashing in identifiers during key derivation (we are not
lawyers, but see US patent 7627760 for example).

Regards,

Alexey and Kenny