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

Kazuho Oku <notifications@github.com> Wed, 30 October 2019 23:33 UTC

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Subject: Re: [quicwg/base-drafts] Add retry integrity tag (#3120)
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@DavidSchinazi 
> encrypting using AES-GCM with an all-zero key and all-zero nonce is just a XOR operation between a known string and the cleartext so the performance cost is very low.

Oh I see what you mean. That's a keen observation. Though, I think that observation also shows the reason some of us thought use of encryption to be beneficial to be pointless.

IIUC, https://github.com/quicwg/base-drafts/pull/3120#pullrequestreview-304931396 suggested using encryption, because it would prevent implementations from using the token without checking the tag. The assumption behind is that AEAD-decryption is going to be an atomic operation.

But as you point out, in this particular case, there is a interesting optimization where endpoints can have a pre-built XOR vector, and just do GCM.

Doesn't that reduce the motivation to use encryption, as it is a complexity to apply XOR?

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