Re: [TLS] confirming the room’s consensus: adopt HKDF PRF for TLS 1.3

Brian Smith <brian@briansmith.org> Wed, 01 April 2015 19:32 UTC

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Date: Wed, 1 Apr 2015 09:32:22 -1000
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From: Brian Smith <brian@briansmith.org>
To: Sean Turner <turners@ieca.com>
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Subject: Re: [TLS] =?utf-8?q?confirming_the_room=E2=80=99s_consensus=3A_adopt_?= =?utf-8?q?HKDF_PRF_for_TLS_1=2E3?=
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Sean Turner <turners@ieca.com> wrote:
> This message is to confirm the consensus reached @ the IETF 92 TLS session in Dallas and at the TLS Interim in Seattle to make the TLS 1.3 PRF be an HKDF-based PRF (see http://datatracker.ietf.org/doc/rfc5869/?include_text=1).
>
> Please indicate whether or not you agree with the consensus by 2015-04-17.  If not, please indicate why.  Also, please note that we’re interested in uncovering new issues not rehashing issues already discussed.

There's a lot of ambiguity in what "HKDF-based" means.

I agree that new versions of TLS should use HKDF-Extract, then
HKDF-Expand, with suitable parameters, as recommended in RFC5869, to
build the keyblock that will be partitioned into keys. I also agree
that TLS extractor should use HKDF in a similar way for new versions
of TLS.

Cheers,
Brian