IETF Logo Mail Archive

Re: [Cfrg] On the differences of Ed25519/448 and how it affects a vote on twoshakes-d

Bryan Ford <brynosaurus@gmail.com> Sat, 12 December 2015 12:14 UTC

Return-Path: <brynosaurus@gmail.com>
X-Original-To: cfrg@ietfa.amsl.com
Delivered-To: cfrg@ietfa.amsl.com
Received: from localhost (ietfa.amsl.com [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 224EB1A710C for <cfrg@ietfa.amsl.com>; Sat, 12 Dec 2015 04:14:07 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2
X-Spam-Level:
X-Spam-Status: No, score=-2 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, FREEMAIL_FROM=0.001, SPF_PASS=-0.001] 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 Pea5idWJYBxq for <cfrg@ietfa.amsl.com>; Sat, 12 Dec 2015 04:14:06 -0800 (PST)
Received: from mail-wm0-x22a.google.com (mail-wm0-x22a.google.com [IPv6:2a00:1450:400c:c09::22a]) (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 D8E261A710D for <cfrg@irtf.org>; Sat, 12 Dec 2015 04:14:04 -0800 (PST)
Received: by wmpp66 with SMTP id p66so5312172wmp.1 for <cfrg@irtf.org>; Sat, 12 Dec 2015 04:14:03 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=content-type:mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=oLgdtyqXW9F+m3u7UYTlGw7mAznT8h3CiGgrDZbCpms=; b=E7BPejaE9Mg5Y+OfycvUNcfdwvnOeIoNIXfBYBsjYwIbcfIARMEimhYxYZYWt5H3SI DzhIKjghlmJblS1KlmgKe/GqI91FKJyRfpQ6a5ikn/io82SUb+Km7SwJQhDWzwrM2Vb6 95ivmweEn05rF2Cse5stijBtXtWTK7Wf0f39VWCsA1hK/9HsmSmMCnrDIgI9AfxDOR7L TfSDKdr0aCLSrzA4KU+x6iv6S5sP3JJJ9DZtSC8Z41/UCWo15KFFk5mUrBeT5+JkqTcI rK0AS7UvAVll2TJfkGTz8mupQDDFYxWkwl/B3hy5XDe1tNb/dAxsjTKuYSN5Q0Et3H4K sYgA==
X-Received: by 10.28.223.212 with SMTP id w203mr12950590wmg.88.1449922443513; Sat, 12 Dec 2015 04:14:03 -0800 (PST)
Received: from [192.168.1.136] (85-218-12-53.dclient.lsne.ch. [85.218.12.53]) by smtp.gmail.com with ESMTPSA id z66sm7514888wmz.7.2015.12.12.04.14.01 (version=TLSv1/SSLv3 cipher=OTHER); Sat, 12 Dec 2015 04:14:01 -0800 (PST)
Content-Type: text/plain; charset="us-ascii"
Mime-Version: 1.0 (1.0)
From: Bryan Ford <brynosaurus@gmail.com>
X-Mailer: iPhone Mail (13B143)
In-Reply-To: <20151212111448.GB6039@LK-Perkele-V2.elisa-laajakaista.fi>
Date: Sat, 12 Dec 2015 13:14:00 +0100
Content-Transfer-Encoding: quoted-printable
Message-Id: <C79B46AA-62EA-4D93-A850-62D85422B9B6@gmail.com>
References: <CAA4PzX18bcS_awPg-YDAoo90537Ot=s_nf7k_Vt75OVSdvtDrQ@mail.gmail.com> <87fuzcng51.fsf@latte.josefsson.org> <20151209125944.GA26766@LK-Perkele-V2.elisa-laajakaista.fi> <566AEB08.9070302@st.com> <566BDBE9.4000808@gmail.com> <20151212111448.GB6039@LK-Perkele-V2.elisa-laajakaista.fi>
To: Ilari Liusvaara <ilariliusvaara@welho.com>
Archived-At: <http://mailarchive.ietf.org/arch/msg/cfrg/06lnAHfz5OPvrqLyclw-_JBloZo>
Cc: cfrg@irtf.org
Subject: Re: [Cfrg] On the differences of Ed25519/448 and how it affects a vote on twoshakes-d
X-BeenThere: cfrg@irtf.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: Crypto Forum Research Group <cfrg.irtf.org>
List-Unsubscribe: <https://www.irtf.org/mailman/options/cfrg>, <mailto:cfrg-request@irtf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/cfrg/>
List-Post: <mailto:cfrg@irtf.org>
List-Help: <mailto:cfrg-request@irtf.org?subject=help>
List-Subscribe: <https://www.irtf.org/mailman/listinfo/cfrg>, <mailto:cfrg-request@irtf.org?subject=subscribe>
X-List-Received-Date: Sat, 12 Dec 2015 12:14:07 -0000

On Dec 12, 2015, at 12:14 PM, Ilari Liusvaara <ilariliusvaara@welho.com> wrote:
> This brings to mind the following (bit crazy):
> 
> - Leave Ed25519 as is.
> - Drop Ed25519ph
> - Add Ed25519dom, with context and hash-signing capabilities.
> - Drop Ed448ph
> - Rename Ed448 to Ed448dom, with context and hash-signing capabilties.

This seems like a potentially pretty reasonable "sweet spot" compromise between the semi-conflicting goals of (a) domain separation, (b) alignment between Ed448 and Ed25519, and  (c) backward compatibility with current Ed25529 uses without prehashing or domain separation. 

The one downside I see is that "pure" Ed25519 wouldn't be domain-separated from ed25519dom, i.e., signatures generated with the former could in principle get misinterpreted as the latter and vice versa. But this is probably a small risk we can live with for backward-compatibility reasons.  And if we still have a non-prehashing version of Ed448, that could still be domain-separated from the prehashing version without creating compatibility concerns as in Ed25519. 

B

> -Ilari

v2.23.0 | Report a Bug | By Email