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Re: [openpgp] OpenPGP SEIP downgrade attack

Werner Koch <wk@gnupg.org> Wed, 07 October 2015 19:41 UTC

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From: Werner Koch <wk@gnupg.org>
To: Peter Gutmann <pgut001@cs.auckland.ac.nz>
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Date: Wed, 07 Oct 2015 21:37:45 +0200
In-Reply-To: <9A043F3CF02CD34C8E74AC1594475C73F4B2C5B4@uxcn10-5.UoA.auckland.ac.nz> (Peter Gutmann's message of "Wed, 7 Oct 2015 13:50:52 +0000")
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Subject: Re: [openpgp] OpenPGP SEIP downgrade attack
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On Wed,  7 Oct 2015 15:50, pgut001@cs.auckland.ac.nz said:

> The reason why I prefer EtM is that it can be pretty trivially retrofitted to
> existing crypto (just add a SHA-256 MAC somewhere) and is compatible with any

But raises the same problems as all data format changes.  When taking up
these trouble why got for a slow method whilst faster methods are
available.

> existing cipher, while whatever AEAD mechanism is chosen (I'm guessing AES-
> GCM, which seems to be fashionable) is purely for AES, there's no Twofish or
> CAST or whatever AEAD mode defined.

OCB works with all 128 bit block length ciphers and is faster than GCM.


Salam-Shalom,

   Werner

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