Re: [openpgp] OpenPGP SEIP downgrade attack

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

Return-Path: <wk@gnupg.org>
X-Original-To: openpgp@ietfa.amsl.com
Delivered-To: openpgp@ietfa.amsl.com
Received: from localhost (ietfa.amsl.com [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 872B61B2F80 for <openpgp@ietfa.amsl.com>; Wed, 7 Oct 2015 12:41:06 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.9
X-Spam-Level:
X-Spam-Status: No, score=-1.9 tagged_above=-999 required=5 tests=[BAYES_00=-1.9] autolearn=ham
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id QEuspMjxtlfH for <openpgp@ietfa.amsl.com>; Wed, 7 Oct 2015 12:41:05 -0700 (PDT)
Received: from kerckhoffs.g10code.com (kerckhoffs.g10code.com [IPv6:2001:aa8:fff1:100::22]) (using TLSv1.2 with cipher DHE-RSA-AES128-SHA (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 6CB231AD2A9 for <openpgp@ietf.org>; Wed, 7 Oct 2015 12:41:05 -0700 (PDT)
Received: from uucp by kerckhoffs.g10code.com with local-rmail (Exim 4.80 #2 (Debian)) id 1ZjuaF-0000GD-NL for <openpgp@ietf.org>; Wed, 07 Oct 2015 21:41:03 +0200
Received: from wk by vigenere.g10code.de with local (Exim 4.84 #3 (Debian)) id 1ZjuX4-0006kt-CW; Wed, 07 Oct 2015 21:37:46 +0200
From: Werner Koch <wk@gnupg.org>
To: Peter Gutmann <pgut001@cs.auckland.ac.nz>
References: <56128436.40607@assured.se> <87y4fh4210.fsf@vigenere.g10code.de> <9A043F3CF02CD34C8E74AC1594475C73F4B28383@uxcn10-5.UoA.auckland.ac.nz> <87k2r04hak.fsf@vigenere.g10code.de> <9A043F3CF02CD34C8E74AC1594475C73F4B2C5B4@uxcn10-5.UoA.auckland.ac.nz>
Organisation: g10 Code GmbH
X-message-flag: Mails containing HTML will not be read! Please send only plain text.
OpenPGP: id=F2AD85AC1E42B367; url=finger:wk@g10code.com
Mail-Followup-To: Peter Gutmann <pgut001@cs.auckland.ac.nz>, "cfrg\@mail.ietf.org" <cfrg@mail.ietf.org>, Jonas Magazinius <jonas.magazinius@assured.se>, "cryptography\@metzdowd.com" <cryptography@metzdowd.com>, "openpgp\@ietf.org" <openpgp@ietf.org>
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")
Message-ID: <87si5m1ncm.fsf@vigenere.g10code.de>
User-Agent: Gnus/5.13 (Gnus v5.13)
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Archived-At: <http://mailarchive.ietf.org/arch/msg/openpgp/ZGGHjDWXN3lCYz5milBEMLoCtns>
Cc: "cfrg@mail.ietf.org" <cfrg@mail.ietf.org>, Jonas Magazinius <jonas.magazinius@assured.se>, "cryptography@metzdowd.com" <cryptography@metzdowd.com>, "openpgp@ietf.org" <openpgp@ietf.org>
Subject: Re: [openpgp] OpenPGP SEIP downgrade attack
X-BeenThere: openpgp@ietf.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: "Ongoing discussion of OpenPGP issues." <openpgp.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/openpgp>, <mailto:openpgp-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/openpgp/>
List-Post: <mailto:openpgp@ietf.org>
List-Help: <mailto:openpgp-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/openpgp>, <mailto:openpgp-request@ietf.org?subject=subscribe>
X-List-Received-Date: Wed, 07 Oct 2015 19:41:06 -0000

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

-- 
Die Gedanken sind frei.  Ausnahmen regelt ein Bundesgesetz.