Re: [TLS] Randomization of nonces

Martin Thomson <martin.thomson@gmail.com> Tue, 16 August 2016 04:56 UTC

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From: Martin Thomson <martin.thomson@gmail.com>
Date: Tue, 16 Aug 2016 14:56:06 +1000
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To: "Paterson, Kenny" <Kenny.Paterson@rhul.ac.uk>
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Subject: Re: [TLS] Randomization of nonces
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On 16 August 2016 at 09:46, Paterson, Kenny <Kenny.Paterson@rhul.ac.uk> wrote:
> Sadly, you can't implement XGCM using an existing AES-GCM API, because of
> the way the MAC (which is keyed) is computed over the ciphertext in the
> standard GCM scheme.


Is there a reason why you can't simply XOR the plaintext stream that
is fed to AES-GCM?

We set N = N XOR HKDF(IKM, salt, label[N], 12), which the paper shows
improves things.  If we also set P = P XOR repeat(HKDF(IKM, salt,
label[P], 16)) would we gain any of the advantages of XCAU?  That
change could be made without needing a new algorithm.