Re: [TLS] open issues for draft-ietf-tls-chacha20-poly1305-00

Martin Thomson <martin.thomson@gmail.com> Tue, 04 August 2015 17:35 UTC

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Date: Tue, 4 Aug 2015 10:35:30 -0700
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From: Martin Thomson <martin.thomson@gmail.com>
To: Wan-Teh Chang <wtc@google.com>
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Subject: Re: [TLS] open issues for draft-ietf-tls-chacha20-poly1305-00
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On 4 August 2015 at 10:24, Wan-Teh Chang <wtc@google.com> wrote:
> The consistency you want to see seems to be
> consistency with the AES GCM cipher suites, rather than with TLS 1.2.


Yes, this is correct.

RFC 5288:
             struct {
                opaque salt[4];
                opaque nonce_explicit[8];
             } GCMNonce;

RFC 6655:
                       struct {
             opaque salt[4];
             opaque nonce_explicit[8];
                       } CCMNonce;

Interestingly, RFC 6655 removes the explicit nonce for DTLS, but DTLS
only (if I'm reading it correctly).

Either way, I think that we should attempt to be consistent with
these.  Which suggests that perhaps we can adopt a zero-length
explicit nonce and borrow the 6655 DTLS construction.

As for the wasted bytes, I don't care for that.  We will fix that later.