Re: [TLS] AAED ciphers: AES-GCM vs AES-EAX/AES-CCM: a meta-analysis

Michael Clark <michael@metaparadigm.com> Tue, 06 January 2015 13:31 UTC

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Date: Tue, 06 Jan 2015 21:30:13 +0800
From: Michael Clark <michael@metaparadigm.com>
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Subject: Re: [TLS] AAED ciphers: AES-GCM vs AES-EAX/AES-CCM: a meta-analysis
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On 6/1/15 6:24 pm, Peter Gutmann wrote:
> Michael Clark <michael@metaparadigm.com>; writes:
>
>> A TLSv1.3 ClientHello and ServerHello extensions could advertise something
>> like this this:
> Ugh, not, we don't need yet more extensions and complexity, we just need a
> single set of options that everyone uses (see Grigg's Law, "There is only one
> cipher suite and that is #1").

I have some alternative ideas. You probably won't like them ;-)

There are different dimensions of simplicity and complexity relating to
composition and layering.

I think the worst problem with TLS is supporting backwards compatibility.

There is a possibility to add symmetry and reduce complexity. I just
posted about HMAC on handshakes and some other comments, that may
actually mean Encrypt-then-MAC is needed, and you just have hmac_null in
the common case where you are satisfied with the 128-bit tag from the
AEAD cipher.

* handshake
    ETM-AEAD[null,hmac_sha2_256]

* application data
    ETM-AEAD[aead-cipher,hmac_null]

* application data with extended authentication
    ETM-AEAD[aead-cipher,hmac_sha2_256]