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

Peter Gutmann <pgut001@cs.auckland.ac.nz> Tue, 06 January 2015 10:27 UTC

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From: Peter Gutmann <pgut001@cs.auckland.ac.nz>
To: "<tls@ietf.org>" <tls@ietf.org>
Thread-Topic: [TLS] AAED ciphers: AES-GCM vs AES-EAX/AES-CCM: a meta-analysis
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Date: Tue, 6 Jan 2015 10:27:04 +0000
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Subject: Re: [TLS] AAED ciphers: AES-GCM vs AES-EAX/AES-CCM: a meta-analysis
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Michael Clark <michael@metaparadigm.com>; writes:

>Before I've read through can we do this with it?
>
>AES-256-GCM + hmac_null   = 128 bits authentication
>AES-256-CBC + hmac_sha128 = 128 bits authentication
>
>AES-256-GCM + hmac_sha128 = 256 bits authentication
>AES-256-CBC + hmac_sha256 = 256 bits authentication
>
>AES-256-GCM + hmac_sha256 = 384 bits authentication
>AES-256-CBC + hmac_sha384 = 384 bits authentication

The MAC is whatever is negotiated for the session, and if you want a shorter
one you can send the truncated-MAC extension (which, however, nothing supports
AFAIK).  Having said that, see my previous message about not needing a
thousand options, we only need one that everyone uses.

Peter.