Re: [TLS] Comments on nonce construction and cipher text size restriction.

Quynh Dang <quynh97@gmail.com> Tue, 24 May 2016 21:19 UTC

Return-Path: <quynh97@gmail.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 04A0B12D557 for <tls@ietfa.amsl.com>; Tue, 24 May 2016 14:19:04 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2.449
X-Spam-Level:
X-Spam-Status: No, score=-2.449 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, FREEMAIL_ENVFROM_END_DIGIT=0.25, FREEMAIL_FROM=0.001, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_LOW=-0.7, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=gmail.com
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 L8JhTkQ_f6C0 for <tls@ietfa.amsl.com>; Tue, 24 May 2016 14:19:02 -0700 (PDT)
Received: from mail-ig0-x22d.google.com (mail-ig0-x22d.google.com [IPv6:2607:f8b0:4001:c05::22d]) (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 1678112D505 for <tls@ietf.org>; Tue, 24 May 2016 14:19:02 -0700 (PDT)
Received: by mail-ig0-x22d.google.com with SMTP id ww4so60241852igb.1 for <tls@ietf.org>; Tue, 24 May 2016 14:19:02 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc; bh=7D7Sh+s+N5GmOmzlY613Mf1egWvcG8LEA4wyu9xgARI=; b=MLsN/AlCHGLJVMUmYxI1G9zgbQz96u8vmxM5PGmKzwID76h91njhO+SZ8aAqlUlirg g0lC8zkhkGjDA0AzfBrod8GK7Ropve5JYbJfksBPUrD+j+giroE73wRKvLhiPAaQWpDr lZk3D8RrqLKZyLUcFDvDCuQmwLeAzFaZYDCOQ0vTraAGQ/Fky6q3yKpgQkk1D+G8yPzp ii0I3Jm2/eOLE3thIQcNtIxPT08eC8bORkUOl+brbp/nrMI/52QQdRbA7ARSB4ZaASm2 XyQGzkx+y9KUfFbSJ2eeB83BB+ifpkdR5NbGA0TH3c44+zYWeLXeqN1RSJ4CFtjQpv6Y +YLg==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:date :message-id:subject:from:to:cc; bh=7D7Sh+s+N5GmOmzlY613Mf1egWvcG8LEA4wyu9xgARI=; b=ZsPkdvudDdL7lVPSwBeSY83X8FrtTn2w8nv/XT7W5zuK95tSW4Hz81rIy+ENCHn8Cp K2Y1Z3X2Z0DRM83DpuVcvEy/Esk/cuWnadHUeg6MVK0hbTbAfIHanbClrHp8VGygtzl8 3l1zskSM1YCD1t7Pv9iKpHMGQxzhZ2NjmNikUMGjBbNl6oyWGgCtFfX1BuksLA75pNST nwqLBecmsU4HKIkRZyX6KPvYdc1JUfr9sKcOWw624YqTzrsRkRoV7gE1ibKE9b+CJiFn pbDPgWeGlx5RzMK0Jxon8dnBaLwmcxZ2gz7UyAVj+7RHG0KSQujRwAWiCWneF4/BMqfk 8UFg==
X-Gm-Message-State: AOPr4FW3Vh6IZggugn7HC9RgOtMCIMCzWae619e45Ekh4q2/p8/5OAe6D6LQSUEq+FAXsM8dvHrHl1pf8Dnu+g==
MIME-Version: 1.0
X-Received: by 10.50.153.166 with SMTP id vh6mr19367127igb.90.1464124741395; Tue, 24 May 2016 14:19:01 -0700 (PDT)
Received: by 10.64.228.131 with HTTP; Tue, 24 May 2016 14:19:01 -0700 (PDT)
Received: by 10.64.228.131 with HTTP; Tue, 24 May 2016 14:19:01 -0700 (PDT)
In-Reply-To: <CABcZeBMMTLbagH0Nq=JdqKGD9tqUbw0+Mw4AJ+kgzototoJQhw@mail.gmail.com>
References: <D369E95C.267A5%qdang@nist.gov> <CABkgnnVAVYDuWUV0EJ=9iJ69KOwYxR=tzRRB+A96qwKmco8qEg@mail.gmail.com> <D36A0B54.267BA%qdang@nist.gov> <CABkgnnUa8G7UJ9BuQ8zHzuwe54-D_gPKFBE9DPSK6C=a-O28Kw@mail.gmail.com> <D36A1CA2.267DC%qdang@nist.gov> <CABcZeBNv1bzaT-y7OscX4M2Q5bQxeFM=XkkqnOvKVpE=f3GFLg@mail.gmail.com> <CAE3-qLRpAU-66prnSbzrbdtgo_Sc4gfaHAdfOJfysNMq61b3wA@mail.gmail.com> <CABcZeBMMTLbagH0Nq=JdqKGD9tqUbw0+Mw4AJ+kgzototoJQhw@mail.gmail.com>
Date: Tue, 24 May 2016 17:19:01 -0400
Message-ID: <CAE3-qLQb832Xn8KqST03XUN8i2v4HVR-ThnHEZQr-uQT0rs9Bw@mail.gmail.com>
From: Quynh Dang <quynh97@gmail.com>
To: Eric Rescorla <ekr@rtfm.com>
Content-Type: multipart/alternative; boundary=e89a8f2355651e2f8405339d1b46
Archived-At: <http://mailarchive.ietf.org/arch/msg/tls/UfRFJESLzHdRdV81dF7oG-OHKEw>
Cc: tls@ietf.org
Subject: Re: [TLS] Comments on nonce construction and cipher text size restriction.
X-BeenThere: tls@ietf.org
X-Mailman-Version: 2.1.17
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: <https://mailarchive.ietf.org/arch/browse/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 May 2016 21:19:04 -0000

If that is what you are worried about, then that would make sense.

Quynh.
On May 24, 2016 4:23 PM, "Eric Rescorla" <ekr@rtfm.com> wrote:

> No, a smaller computation (say 2^{64}) and then collecting 2^{40}
> connections all of which encipher the same plaintext (e.g., "GET /...")
>
> -Ekr
>
>
> On Tue, May 24, 2016 at 1:13 PM, Quynh Dang <quynh97@gmail.com> wrote:
>
>> Are you worried about 2^96 precomputation and the risk of 1/2^32 of
>> cracking your key?
>>
>> Quynh.
>> On May 24, 2016 3:05 PM, "Eric Rescorla" <ekr@rtfm.com> wrote:
>>
>>>
>>>
>>> On Tue, May 24, 2016 at 12:00 PM, Dang, Quynh (Fed) <quynh.dang@nist.gov
>>> > wrote:
>>>
>>>>
>>>>
>>>> On 5/24/16, 2:42 PM, "Martin Thomson" <martin.thomson@gmail.com> wrote:
>>>>
>>>> >On 24 May 2016 at 10:46, Dang, Quynh (Fed) <quynh.dang@nist.gov>
>>>> wrote:
>>>> >>>We discussed this at quite some length.  I originally took your
>>>> >>>position, but the IVs add an extra layer of safety at very little
>>>> >>>cost.
>>>> >>
>>>> >> I don¹t see any extra layer here.
>>>> >
>>>> >
>>>> >The argument here is that there are only 2^128 keys and some protocols
>>>> >have predictable plaintext.  A predictable nonce would allow an
>>>> >attacker to do some pre-calculation with a large number of keys to get
>>>> >a chance of a collision (and a break).  It's a long bow, but not
>>>> >entirely implausible.
>>>>
>>>> Ciphers use nonces are designed/proved to be secure when nonces are
>>>> predictable: nonces are not random values.
>>>>
>>>
>>> I think you may be misunderstanding. There is a time/space tradeoff here
>>> when the
>>> nonces are predictable that does not exist when they are random. This is
>>> not a
>>> vulnerability in the cipher and applies even if the keystream generator
>>> at the core
>>> of the cipher is PRF_k(nonce).
>>>
>>> -Ekr
>>>
>>>
>>>> >
>>>>
>>>>
>>>
>>> _______________________________________________
>>> TLS mailing list
>>> TLS@ietf.org
>>> https://www.ietf.org/mailman/listinfo/tls
>>>
>>>
>