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Re: [quicwg/base-drafts] Encrypting Retry token (#3274)

MikkelFJ <notifications@github.com> Mon, 09 December 2019 20:30 UTC

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Date: Mon, 09 Dec 2019 12:30:21 -0800
From: MikkelFJ <notifications@github.com>
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Subject: Re: [quicwg/base-drafts] Encrypting Retry token (#3274)
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Using raw GHASH over GMAC would avoid the need for an AES module in hardware and only require carryless multiplication (CLMUL) for efficient operation, but I can't imagine where that case would be very relevant. Even on low-end microcontrollers it is more likely you have SHA-256 and AES hardware than CLMUL, at least for now. From that perspective Poly1305 would be more efficient, but given the nature of Retry and the dependence on AES-GCM elsewhere in the protocol, GMAC or GHASH makes more sense. GMAC is much simpler than GHASH because it can use existing libraries. If GHASH were to be used directly one would have to ensure that it is safe in the applied context and with the supplied key whereas GCM is well understood even if it costs a few block encryptions extra.

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