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Re: [IPsec] ChaCha20 & Poly1305, AEAD and other modes

Daniel Migault <mglt.ietf@gmail.com> Mon, 10 March 2014 08:43 UTC

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Date: Mon, 10 Mar 2014 09:43:05 +0100
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From: Daniel Migault <mglt.ietf@gmail.com>
To: Yoav Nir <ynir.ietf@gmail.com>
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Subject: Re: [IPsec] ChaCha20 & Poly1305, AEAD and other modes
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Hi,

My understanding is that Poly1305 and chacha20 are provided as
"alternatives" to SHA* or AES*. Specific devices with AES
accelerations may be willing, for performance optimization, to use
Poly1305 instead of SHA with AES. For this reason it might be better
to have:
    - chacha20 as a stand-alone cipher
    - Poly1305 as a stand-alone MAC

On the other hand, providing the AEAD chacha20-poly1305 may be helpful
for end users or admins. Especially if security consideration
recommends AEAD. Would it bring too much complexity to also define
AEAD chacha20-poly1305?

BR
Daniel



On Mon, Mar 10, 2014 at 9:15 AM, Yoav Nir <ynir.ietf@gmail.com> wrote:
>
>
>
> On Mon, Mar 10, 2014 at 8:00 AM, Yaron Sheffer <yaronf.ietf@gmail.com>
> wrote:
>>
>> Hi Yoav,
>>
>> Can you explain why we need Poly1305 at all? We have SHA-2 and will
>> probably adopt Keccak (SHA-3), so it's not like we don't have a backup.
>
>
> Sure.  Poly1305 is fast.Faster than SHA-1, SHA-2, and Keccak. I haven't
> compared it to GMAC on Intel, but that is fast only becuase it has special
> Intel instructions like PCLMULQD. Both ChaCha and Poly1305 can be fast in a
> plain C implementation, so they're fast on any platform.  Poly1305 needs
> another algorithm to generate the per-message keys. That could be AES as in
> DJB's original paper, or it can be ChaCha as in this draft (with or without
> the AEAD).
>
>>
>> Let me suggest that we adopt *only* ChaCha20, which can be combined with
>> any integrity protection algorithm in the normal ESP way. Is there any extra
>> value (maybe code sharing?) in predefining an AEAD?
>
>
> The AEAD version is already in at least one crypto library (NSS as used in
> Chrome) and there's a patch that AGL donated to OpenSSL (not in there yet).
> So in addition to AEADs being fashionable, this combination makes sense for
> performance, especially on non-Intel platforms.
>
> Yoav
>
>
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-- 
Daniel Migault
Orange Labs -- Security
+33 6 70 72 69 58

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