Re: [TLS] padding bug

Michael D'Errico <mike-list@pobox.com> Tue, 24 September 2013 16:01 UTC

Return-Path: <mike-list@pobox.com>
X-Original-To: tls@ietfa.amsl.com
Delivered-To: tls@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id C8EDD11E8177 for <tls@ietfa.amsl.com>; Tue, 24 Sep 2013 09:01:36 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2.557
X-Spam-Level:
X-Spam-Status: No, score=-2.557 tagged_above=-999 required=5 tests=[AWL=0.042, BAYES_00=-2.599]
Received: from mail.ietf.org ([12.22.58.30]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id DfsHvkYr33-G for <tls@ietfa.amsl.com>; Tue, 24 Sep 2013 09:01:24 -0700 (PDT)
Received: from sasl.smtp.pobox.com (a-pb-sasl-quonix.pobox.com [208.72.237.25]) by ietfa.amsl.com (Postfix) with ESMTP id DA6DC11E817D for <tls@ietf.org>; Tue, 24 Sep 2013 09:01:01 -0700 (PDT)
Received: from sasl.smtp.pobox.com (unknown [127.0.0.1]) by a-pb-sasl-quonix.pobox.com (Postfix) with ESMTP id 16CBFD837; Tue, 24 Sep 2013 12:00:56 -0400 (EDT)
DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=pobox.com; h=message-id :date:from:mime-version:to:cc:subject:references:in-reply-to :content-type:content-transfer-encoding; s=sasl; bh=we6ZQQQAKXO/ xHq67FxLoWuBPTw=; b=Scqm8ydmFIUtMMBChJ4AFp9/sSgIUKAh4q901Or7pr12 t6ntu7mIXmjxAMpRlP9nlI3HtDHih0+3on/O+pJ8cULR2Fd+r2YfHc6lq9rhX2sI tO3vmFUZUfgAtUJuUuwzOAziC/1ghB+qPrbCSWGmcddgkbYjLnDrcwMhSyJU4Tg=
DomainKey-Signature: a=rsa-sha1; c=nofws; d=pobox.com; h=message-id:date :from:mime-version:to:cc:subject:references:in-reply-to :content-type:content-transfer-encoding; q=dns; s=sasl; b=i2sGRk RC7G+Myp2pkjZfuMJkiKhgShCkSitr6VrLSx5Pib5QMNK2gmIqcfcMHm6WqcIrD0 LXQwPGMYVwZfejVSDBlvJYmugE0NaLRgsuarSEYL0eV4STbjb5b45uajKVjE2DLF /mQOxvNkpSzxOQOaUbm0xEPTqe3chbsFScv5k=
Received: from a-pb-sasl-quonix.pobox.com (unknown [127.0.0.1]) by a-pb-sasl-quonix.pobox.com (Postfix) with ESMTP id 0C709D836; Tue, 24 Sep 2013 12:00:56 -0400 (EDT)
Received: from iMac.local (unknown [24.234.153.62]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by a-pb-sasl-quonix.pobox.com (Postfix) with ESMTPSA id 53992D835; Tue, 24 Sep 2013 12:00:55 -0400 (EDT)
Message-ID: <5241B736.60708@pobox.com>
Date: Tue, 24 Sep 2013 09:00:54 -0700
From: Michael D'Errico <mike-list@pobox.com>
User-Agent: Thunderbird 2.0.0.24 (Macintosh/20100228)
MIME-Version: 1.0
To: Peter Gutmann <pgut001@cs.auckland.ac.nz>
References: <9A043F3CF02CD34C8E74AC1594475C735567C914@uxcn10-6.UoA.auckland.ac.nz>
In-Reply-To: <9A043F3CF02CD34C8E74AC1594475C735567C914@uxcn10-6.UoA.auckland.ac.nz>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
X-Pobox-Relay-ID: 7EAFE7DA-2532-11E3-9ED8-CE710E5B5709-38729857!a-pb-sasl-quonix.pobox.com
Cc: "<tls@ietf.org>" <tls@ietf.org>
Subject: Re: [TLS] padding bug
X-BeenThere: tls@ietf.org
X-Mailman-Version: 2.1.12
Precedence: list
List-Id: "This is the mailing list for the Transport Layer Security working group of the IETF." <tls.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/tls>, <mailto:tls-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/tls>
List-Post: <mailto:tls@ietf.org>
List-Help: <mailto:tls-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/tls>, <mailto:tls-request@ietf.org?subject=subscribe>
X-List-Received-Date: Tue, 24 Sep 2013 16:01:40 -0000

Peter Gutmann wrote:
> 
> TLS has for some years now provided for MAC truncation to a
> range of sizes.

I believe you are confusing the max_fragment_length extension
with truncated_hmac.  Truncated HMAC provides only one size,
80 bits, with the motivation being bandwidth constraints.

Mike