Re: [quicwg/base-drafts] Add retry integrity tag (#3120)

MikkelFJ <notifications@github.com> Wed, 30 October 2019 21:56 UTC

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Date: Wed, 30 Oct 2019 14:55:58 -0700
From: MikkelFJ <notifications@github.com>
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Subject: Re: [quicwg/base-drafts] Add retry integrity tag (#3120)
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@DavidSchinazi on AES-GCM that is not correct: The crypto part yes, but you do not encrypt you only GHASH because it is AEAD only. GHASH is a 128-bit carryless multiplication over a Galois Field which completes the checksum. If you CLMUL instructions this is efficient, otherwise not so much. That is where Poly1305 is a gain. CLMUL is not very common on misc. controllers even if they have other accelerations, at least for the time being. E.g. ESP8266.

I agree that AES-GCM is the right choice given the circumstances but I think Poly1305 would be better for initial and retry because it would work in a broader range. The benefit of AES-GCM is that highly loaded servers will have the necessary accelleration and may slow down on AES-GCM - even if this is a tiny fraction of the overall connection cost, it may be important as it fends of noise from the broader internet.

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