Re: [TLS] Consensus for AEAD IV

Russ Housley <housley@vigilsec.com> Fri, 24 April 2015 21:01 UTC

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From: Russ Housley <housley@vigilsec.com>
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Date: Fri, 24 Apr 2015 17:00:26 -0400
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To: Joseph Salowey <joe@salowey.net>
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Subject: Re: [TLS] Consensus for AEAD IV
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Joe:

> On Fri, Apr 24, 2015 at 1:00 PM, Martin Thomson <martin.thomson@gmail.com> wrote:
> On 24 April 2015 at 10:10, Joseph Salowey <joe@salowey.net> wrote:
> > The general consensus on the list seems to prefer to derive "IV" and use it
> > to make the AEAD nonce less predictable. Most folks seemed to be OK with
> > this approach.    In Dallas, there was significant support for using the
> > derived "IV" as a per session XOR mask for the counter.  If you have
> > objections to this approach please respond on the list by May 1, 2015 .
> 
> 
> You aren't being particularly precise about the process here.
> 
> I believe that these were the two options that were most debated:
> 
> a)  nonce = zeroes(N_MIN) XOR counter
> b)  nonce = HKDF(...., N_MIN) XOR counter
> 
> Did you mean the latter option?
> 
> [Joe] Yes, the later where the quantity XORed with the counter is derived during the handshake.  

If the computation is done in an HSM-friendly fashion, I am supportive.

Russ