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

Yoav Nir <ynir.ietf@gmail.com> Mon, 13 October 2014 13:32 UTC

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From: 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 Oct 13, 2014, at 3:41 PM, Yoav Nir <ynir.ietf@gmail.com> wrote:

> 
> 
>> - RFC5116 recomends specifying just how badly things blow up
>>  if nonce is reused (AFAIK, XOR of plaintexts is revealed and
>>  arbitrary messages with that nonce may be forged).
> 
> Same authentication key and same keystream, so at least the XOR of the plaintexts is revealed and the same one-time Poly1305 is used. So if you know the plaintext and can choose the nonce, you will be able to encrypt another arbitrary message, but you will still fail tag calculation. I’ll add something to the security considerations.
> 
>> Also, writing IANA consideration to register this
>> (AEAD_CHACHA20_POLY1305?) could be useful (as already suggested by
>> someone). Apparently the registry is called "AEAD algorithms" (at
>> least it is that way on IANA site, even if I can't find that in
>> RFC 5116). 
> 
> Will do.
> 

OK. Done and done.

Thanks

Yoav