Re: [openpgp] AEAD Chunk Size

"Neal H. Walfield" <neal@walfield.org> Wed, 13 March 2019 13:27 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 E6C8C126DFA for <openpgp@ietfa.amsl.com>; Wed, 13 Mar 2019 06:27:23 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: 0.001
X-Spam-Level:
X-Spam-Status: No, score=0.001 tagged_above=-999 required=5 tests=[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 4eIcDLlNNJgx for <openpgp@ietfa.amsl.com>; Wed, 13 Mar 2019 06:27:22 -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 E633B124B0C for <openpgp@ietf.org>; Wed, 13 Mar 2019 06:27:21 -0700 (PDT)
Received: from p54abd93f.dip0.t-ipconnect.de ([84.171.217.63] 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 1h43uf-0007S9-MD; Wed, 13 Mar 2019 13:27:17 +0000
Date: Wed, 13 Mar 2019 14:27:17 +0100
Message-ID: <87r2bax5u2.wl-neal@walfield.org>
From: "Neal H. Walfield" <neal@walfield.org>
To: Derek Atkins <derek@ihtfp.com>
Cc: Vincent Breitmoser <look@my.amazin.horse>, Werner Koch <wk@gnupg.org>, openpgp@ietf.org
In-Reply-To: <sjmy35isypu.fsf@securerf.ihtfp.org>
References: <87d0n174w6.fsf@wheatstone.g10code.de> <87mumh33nc.wl-neal@walfield.org> <3GFS71V7BTJNZ.29C5TO8OY0O44@my.amazin.horse> <sjmy35isypu.fsf@securerf.ihtfp.org>
User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM/1.14.9 (=?ISO-8859-4?Q?Goj=F2?=) 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/4q3klPq0lviXpdS7HJ7MBuDrok4>
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: Wed, 13 Mar 2019 13:27:24 -0000

On Wed, 13 Mar 2019 14:14:37 +0100,
Derek Atkins wrote:
> Vincent Breitmoser <look@my.amazin.horse> writes:
> 
> >> The chunking was introduced for just one purpose: To be able to detect rare
> >> transmission errors earlier than at the end of the message.
> >
> > ...really? All this is just to save a few cpu cycles in the rare cases of data
> > corruption that should have been handled by other layers (filesystem / transport
> > layer) in the first place? Why even bother?
> 
> No, it is more than that.  Imagine using OpenPGP to encrypt a full
> filesystem to tape backup.  You necessarily want to be able to chunk
> that as you are saving (and restoring).

I don't think Vincent is disputing the validity of Werner's use case
per se.  I think he is saying the marginal utility of that is tiny
(it's "just a performance improvement") relative to ciphertext
integrity (a security property).