Re: [Cfrg] erratum for hmac what do we think...

"Valery Smyslov" <svanru@gmail.com> Thu, 02 February 2017 13:21 UTC

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From: "Valery Smyslov" <svanru@gmail.com>
To: "'Stephen Farrell'" <stephen.farrell@cs.tcd.ie>, "'cfrg@irtf.org'" <Cfrg@irtf.org>
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Date: Thu, 2 Feb 2017 16:21:43 +0300
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Subject: Re: [Cfrg] erratum for hmac what do we think...
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Hi Stephen,

I would let cryptographers decide whether it is a real problem
(I'm not a cryptographer), but the proposed resolution 
will break existing standards and implementations.
For example, in IKEv2 there is a requirement that 
PRFs MUST accept keys of any length and HMAC is widely
used as PRF (e.g. PRF_HMAC_SHA1 is currently MTI).
And since nonces are used as a PRF key for SKEYSEED 
computation in IKEv2, the key may be quite long. 
So, regardless whether this is a real problem,
the proposed resolution looks bad.

Regards,
Valery Smyslov.


> Hiya,
> 
> There's an erratum posted for hmac [1] where I'd be
> interested in what folks here think.
> 
> I'm unsure if this is a real problem, esp given that
> there are I guess a lot of implementations.
> 
> And even if it were a real problem, I'm not sure we'd
> want that fix.
> 
> Opinions welcome...
> 
> Thanks,
> S.
> 
> [1]
> https://www.rfc-
> editor.org/errata_search.php?rfc=2104&eid=4809&rec_status=15&area_acronym=&errata_type=&wg_ac
> ronym=&submitter_name=&stream_name=&submit_date=&presentation=records