Re: [openpgp] AEAD Chunk Size

"Neal H. Walfield" <neal@walfield.org> Tue, 19 March 2019 08:32 UTC

Return-Path: <neal@walfield.org>
X-Original-To: openpgp@ietfa.amsl.com
Delivered-To: openpgp@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id A891E1311F8 for <openpgp@ietfa.amsl.com>; Tue, 19 Mar 2019 01:32:09 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.899
X-Spam-Level:
X-Spam-Status: No, score=-1.899 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RCVD_IN_DNSWL_NONE=-0.0001, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no
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 aIpzGEqvht8f for <openpgp@ietfa.amsl.com>; Tue, 19 Mar 2019 01:32:07 -0700 (PDT)
Received: from mail.dasr.de (mail.dasr.de [217.69.77.164]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id AEC931274A1 for <openpgp@ietf.org>; Tue, 19 Mar 2019 01:32:07 -0700 (PDT)
Received: from p57b22663.dip0.t-ipconnect.de ([87.178.38.99] helo=grit.huenfield.org.walfield.org) by mail.dasr.de with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.86_2) (envelope-from <neal@walfield.org>) id 1h6AAG-0007Bp-R3; Tue, 19 Mar 2019 08:32:04 +0000
Date: Tue, 19 Mar 2019 09:32:04 +0100
Message-ID: <87ftrji7sr.wl-neal@walfield.org>
From: "Neal H. Walfield" <neal@walfield.org>
To: Bill Frantz <frantz@pwpconsult.com>, openpgp@ietf.org
In-Reply-To: <87r2b348z5.fsf@wheatstone.g10code.de>
References: <r480Ps-10143i-149CE78B9B3A43A29B3D767B6660A08D@Williams-MacBook-Pro.local> <87r2b348z5.fsf@wheatstone.g10code.de>
User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM/1.14.9 (Gojō) APEL/10.8 EasyPG/1.0.0 Emacs/24.5 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO)
MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue")
Content-Type: text/plain; charset="US-ASCII"
Archived-At: <https://mailarchive.ietf.org/arch/msg/openpgp/50akpJF_-djSUSusJTWvs0lt2PE>
Subject: Re: [openpgp] AEAD Chunk Size
X-BeenThere: openpgp@ietf.org
X-Mailman-Version: 2.1.29
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: Tue, 19 Mar 2019 08:32:10 -0000

On Tue, 19 Mar 2019 08:30:22 +0100,
Werner Koch wrote:
> On Mon, 18 Mar 2019 14:11, frantz@pwpconsult.com said:
> 
> > To protect against truncation attacks you can borrow an idea from the
> > database people and not commit your changes until you have a complete
> > message.
> 
> Right.  And you need to do that anyway because authenticated encryption
> doesn't tell you anything about the origin of the message and thus you
> need to check the signature of the message after it has been completely
> decrypted (at least with OpenPGP and CMS).  Anyone can send malicious
> content and AE doesn't protect against processsing such content.

I agree with you that AEAD + signed chunks is even better.  But,
streaming AEAD still provides a significant improvement relative to
the status quo: it protects against EFAIL-style exfiltration attacks.