Re: [Cfrg] RGLC on draft-irtf-cfrg-chacha20-poly1305-01.txt

Adam Langley <agl@imperialviolet.org> Sun, 12 October 2014 17:23 UTC

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From: Adam Langley <agl@imperialviolet.org>
To: Yoav Nir <ynir.ietf@gmail.com>
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Subject: Re: [Cfrg] RGLC on draft-irtf-cfrg-chacha20-poly1305-01.txt
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On Sun, Oct 12, 2014 at 8:00 AM, Yoav Nir <ynir.ietf@gmail.com> wrote:
>>  It obviously takes AAD since section 2.8 mentions it as something to
>> include as input to AEAD_CHACHA20-POLY1305. So I'm suggesting you
>> define what AAD looks like when it is delivered to the mode: "Distinct
>> AAD shall be concatenated into a single input to
>> AEAD_CHACHA20-POLY1305", for example.
>
> OK. I’ll add a sentence like that.

Note that concatenating distinct AD inputs is not safe: ["a", "bc"] is
then ambiguous with ["ab", "c"]. Applications are free to use any
scheme they want, but concatenation shouldn't be implicitly endorsed.


Cheers

AGL

-- 
Adam Langley agl@imperialviolet.org https://www.imperialviolet.org