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Re: [Cfrg] AEAD outputs and RFC 7539 (ChaCha20-Poly1305)

Yoav Nir <ynir.ietf@gmail.com> Tue, 24 May 2016 06:02 UTC

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From: Yoav Nir <ynir.ietf@gmail.com>
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Date: Tue, 24 May 2016 09:02:19 +0300
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To: Martin Thomson <martin.thomson@gmail.com>
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Cc: Adam Langley <agl@imperialviolet.org>, cfrg@ietf.org
Subject: Re: [Cfrg] AEAD outputs and RFC 7539 (ChaCha20-Poly1305)
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> On 24 May 2016, at 2:57 AM, Martin Thomson <martin.thomson@gmail.com> wrote:
> 
> On 23 May 2016 at 19:36, Adam Langley <agl@imperialviolet.org> wrote:
>> I favour the model of RFC5116, but it's not universal. There are
>> certainly cases where the separate parts are used, for example when
>> encrypting in place and storing tags out of band.
> 
> 
> I'm sure those people with special needs can use special tools.  The
> only reason I point this out is that it makes it harder to point at
> ChaCha... as an AEAD.

Seems right. Perhaps the report should say:

OLD:
  The output from the AEAD is twofold:

New:
  The output from the AEAD is a concatenation of two parts:

Yoav

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