Re: [Cfrg] Authenticated Encryption with AES-CBC and HMAC-SHA, version 01

"Dan Harkins" <dharkins@lounge.org> Tue, 13 November 2012 02:58 UTC

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Date: Mon, 12 Nov 2012 18:58:12 -0800 (PST)
From: "Dan Harkins" <dharkins@lounge.org>
To: "Peter Gutmann" <pgut001@cs.auckland.ac.nz>
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Cc: mcgrew@cisco.com, cfrg@irtf.org, jose@ietf.org
Subject: Re: [Cfrg] Authenticated Encryption with AES-CBC and HMAC-SHA, version 01
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On Mon, November 12, 2012 5:43 pm, Peter Gutmann wrote:
> Dan Harkins <dharkins@lounge.org> writes:
>
>>The downside is that it's slower than GCM but is probably faster than
>> CBC-
>>HMAC with SHA2.
>
> A much bigger downside is that it requires two passes over the data,
> making it
> unusable with any streaming implementation.  This limits its applicability
> to
> protocols with very short PDUs.

  That is exactly why it's slower than GCM. But the alternative that's being
discussed for JOSE does 2 passes of the data anyway, one with HMAC-SHA256
and another with AES-CBC, so it sounds a little hard to believe that 2 passes
is a limitation for the application at hand.

  Dan.