Return-Path: X-Original-To: cfrg@ietfa.amsl.com Delivered-To: cfrg@ietfa.amsl.com Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 3CD121294CF for ; Mon, 27 Mar 2017 03:51:36 -0700 (PDT) X-Virus-Scanned: amavisd-new at amsl.com X-Spam-Flag: NO X-Spam-Score: -1.667 X-Spam-Level: X-Spam-Status: No, score=-1.667 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, HTML_MESSAGE=0.001, MISSING_HEADERS=1.021, RCVD_IN_DNSWL_LOW=-0.7, SPF_PASS=-0.001, T_KAM_HTML_FONT_INVALID=0.01, URIBL_BLOCKED=0.001] autolearn=no 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 z9Jr_Ziz8zXX for ; Mon, 27 Mar 2017 03:51:33 -0700 (PDT) Received: from mail-yw0-x22b.google.com (mail-yw0-x22b.google.com [IPv6:2607:f8b0:4002:c05::22b]) (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 A531C12947B for ; Mon, 27 Mar 2017 03:51:33 -0700 (PDT) Received: by mail-yw0-x22b.google.com with SMTP id i203so28112480ywc.3 for ; Mon, 27 Mar 2017 03:51:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:in-reply-to:references:from:date:message-id:subject:cc; bh=NwuXKerL/S7v5bXrqf16nGtfg7dLgJ9+XU2wKps3NNc=; b=SI9dM/WQOcdy5GzEr+IJW83QGw2CIJeYHXI7DOxEboYUkOIvzOrFP+oTRyE9JWcJgV 7OKMJmj4mgDGC9pXaNKAqOYx6T1V20XqILp7p+01xLwCESRUaxVbs1ceuNKXMYEkBnyT y5wFSmEvTsfWnxIiD9jLZN8ap8oZJCWYRxWo87RnQojhcBkpyF8PewspbeIITdYIPEns 9i1jdKqfUWXlsBFAV3s+GjSNDVUX42UzUZmDS6XUrPth1ihuLboTFSQmMih1aug/ALk/ C2r2QtZsvwoI3Jsg4gbhcihEPh4U8g0A7X3nGzLbm6/POVguNAeHdsPSrQjO/EjE94ex dq5Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:cc; bh=NwuXKerL/S7v5bXrqf16nGtfg7dLgJ9+XU2wKps3NNc=; b=ixhNnvI4STqie5MFbpppaN5Fx9PZ8sAAZeuwmCFpw2/T67eIVKcVsz0CqT6jRbbEAI iNXYQsgLnr/rAfr7izU/BqVWjiGXO++hks0pLc662+mOseNyjjOKsnyCxxaUQNEmntu0 H/VopY3dYDcmvp849n6xefvogk6nZNJeQ5M0/DI8Utef2bzjulxPXlBB/UB8h7e4X7Tf 2/JA0YF+z1CraJ4+vLk74HAN3DAcZl+Qck5nvd+jpp+7OhGZnIfs4PC/LfXeX2hZ84Mq lJuVl+CHcKK3AjDLBh3QlxZGiVhC+VaOCHnaKSH/9UE/aEYU6hdTPKFARiPQUAgwQOyH GU6A== X-Gm-Message-State: AFeK/H367hS0A3khXqnuBWM1uxiXy+lpE7JnwH9KUVTEPPzA5NZXCOtkTH81aYCUNZ5bAhQxFFGOvxoyS3f7mA== X-Received: by 10.37.80.208 with SMTP id e199mr15323015ybb.165.1490611892717; Mon, 27 Mar 2017 03:51:32 -0700 (PDT) MIME-Version: 1.0 Received: by 10.83.67.5 with HTTP; Mon, 27 Mar 2017 03:51:17 -0700 (PDT) In-Reply-To: <149061159741.30566.11599293166376872082@ietfa.amsl.com> References: <149061159741.30566.11599293166376872082@ietfa.amsl.com> From: Dmitry Khovratovich Date: Mon, 27 Mar 2017 12:51:17 +0200 Message-ID: Cc: cfrg@ietf.org Content-Type: multipart/alternative; boundary=001a113ea1465d10b2054bb4201b Archived-At: Subject: Re: [Cfrg] I-D Action: draft-irtf-cfrg-argon2-02.txt X-BeenThere: cfrg@irtf.org X-Mailman-Version: 2.1.22 Precedence: list List-Id: Crypto Forum Research Group List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 27 Mar 2017 10:51:36 -0000 --001a113ea1465d10b2054bb4201b Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Some comments on a new draft:Variants Argon2 fills M bytes of memory in T iterations over it, with M and T being the parameters supplied to Argon2 and determining its performance. Speed on a typical server is linear in the MT product. The Argon2 family has three variants: I, D, and ID, which differ in the way of reusing memory that has been filled. The I variant makes queries with predictable addresses, whereas D determines the addresses on the fly depending on the current state (and thus the password). The ID variant follows I for the first half of the memory used and D for the rest and while overwriting. Side-channels The side-channel attacks, which are of still rising concern in the security community, are applicable to the D variant as the memory addresses and thus information about the password or other secret inputs can be determined from the timing leaks. The I variant is completely invulnerable to this attack, and the ID variant provides only a constant factor improvement for the attacker. Hardware and tradeoffs The M and T parameters determine the cost of bruteforcing passwords on custom hardware, which is proportional to M2T if we follow the traditional time-area product metric. The time-memory tradeoff analysis [2] shows that the bruteforce cost for the I variant can be changed to M2T/Q(M,T) for some quality function Q. For instance, Q(230,1)=3D5, Q(230,4)=3D2.5. The D variant is invulnerable to the approach [2], and the savings factor in the ID variant is upper bounded by factor 2 for all parameters. Defender tradeoff and ultimate recommendations In public and private conversations with security architects in the industry we learned that the bottleneck in a system employing the password-hashing function is the function latency rather than memory costs. We then assume that a rational defender would like to maximize the bruteforce costs for the attacker equipped with a list of hashes, salts, and timing information, for fixed computing time on the defender=E2=80=99s = machine. In this assumption the defender keeps the MT product constant and maximizes the losses M/Q(M,T). The authors of [2] provides us with attack cost estimates for constant MT =3D 228,230,232 (measured in iteration-bytes) We ultimately recommend the ID variant with T=3D1 and maximum M as a defaul= t setting for all environments, which is secure against side-channel attacks and prohibit adversarial advantage on dedicated bruteforce hardware. References [1] =E2=80=9CEfficiently Computing Data-Independent Memory-Hard Functions= =E2=80=9D [2] =E2=80=9CTowards Practical Attacks on Argon2i and Balloon Hashing=E2=80= =9D On Mon, Mar 27, 2017 at 12:46 PM, wrote: > > A New Internet-Draft is available from the on-line Internet-Drafts > directories. > This draft is a work item of the Crypto Forum of the IETF. > > Title : The memory-hard Argon2 password hash and > proof-of-work function > Authors : Alex Biryukov > Daniel Dinu > Dmitry Khovratovich > Simon Josefsson > Filename : draft-irtf-cfrg-argon2-02.txt > Pages : 26 > Date : 2017-03-27 > > Abstract: > This document describes the Argon2 memory-hard function for password > hashing and proof-of-work applications. We provide an implementer > oriented description together with sample code and test vectors. The > purpose is to simplify adoption of Argon2 for Internet protocols. > > > The IETF datatracker status page for this draft is: > https://datatracker.ietf.org/doc/draft-irtf-cfrg-argon2/ > > There are also htmlized versions available at: > https://tools.ietf.org/html/draft-irtf-cfrg-argon2-02 > https://datatracker.ietf.org/doc/html/draft-irtf-cfrg-argon2-02 > > A diff from the previous version is available at: > https://www.ietf.org/rfcdiff?url2=3Ddraft-irtf-cfrg-argon2-02 > > > Please note that it may take a couple of minutes from the time of > submission > until the htmlized version and diff are available at tools.ietf.org. > > Internet-Drafts are also available by anonymous FTP at: > ftp://ftp.ietf.org/internet-drafts/ > > _______________________________________________ > Cfrg mailing list > Cfrg@irtf.org > https://www.irtf.org/mailman/listinfo/cfrg > --=20 Best regards, Dmitry Khovratovich --001a113ea1465d10b2054bb4201b Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable

Some comments on a new draft:<= /font>

Variants

Argon2 fills M bytes of memory in T i= terations over it, with M and T being the parameters supplied to Argon2 and= determining its performance. Speed on a typical server is linear in the MT= product.


The Argon2 family has three variants: I, D, and ID, which dif= fer in the way of reusing memory that has been filled. The I variant makes = queries with predictable addresses, whereas D determines the addresses on t= he fly depending on the current state (and thus the password). The ID varia= nt follows I for the first half of the memory used and D for the rest and w= hile overwriting.

Side-channels

The side-channe= l attacks, which are of still rising concern in the security community, are= applicable to the D variant as the memory addresses and thus information a= bout the password or other secret inputs can be determined from the timing = leaks. The I variant is completely invulnerable to this attack, and the ID = variant provides only a constant factor improvement for the attacker.

Hardware and tradeoffs

The M and T parameters determine the c= ost of bruteforcing passwords on custom hardware, which is proportional to = M2T if we = follow the traditional time-area product metric. The time-memory tradeoff a= nalysis [2] shows that the bruteforce cost for the I variant can be changed= to M2<= /span>T/Q(= M,T) for some quality function Q. For instance, Q(230,1)=3D5, Q(230,4)=3D2.5.


<= p dir=3D"ltr" style=3D"line-height:1.38;margin-top:0pt;margin-bottom:0pt"><= span style=3D"font-size:10pt;font-family:arial;color:rgb(0,0,0);background-= color:transparent;vertical-align:baseline;white-space:pre-wrap">The D varia= nt is invulnerable to the approach [2], and the savings factor in the ID va= riant is upper bounded by factor 2 for all parameters.

= Defender tradeoff and ultimate recommendations

In public and privat= e conversations with security architects in the industry we learned that th= e bottleneck in a system employing the password-hashing function is the fun= ction latency rather than memory costs. We then assume that a rational defe= nder would like to maximize the bruteforce costs for the attacker equipped = with a list of hashes, salts, and timing information, for fi= xed computing time on the defender=E2=80=99s machine.=C2=A0 In this assumption= the defender keeps the MT product constant and maximizes the losses M/Q(M,= T). The authors of [2] provides us with attack cost estimates for constant = MT =3D 228= ,230,232 (measured i= n iteration-bytes)


We ultimately recommend the ID variant with T=3D1 an= d maximum M as a default setting for all environments, which is secure agai= nst side-channel attacks and prohibit adversarial advantage on dedicated br= uteforce hardware.


On Mon, Mar 27, 2017 at 12:46 PM, &= lt;internet-d= rafts@ietf.org> wrote:

A New Internet-Draft is available from the on-line Internet-Drafts director= ies.
This draft is a work item of the Crypto Forum of the IETF.

=C2=A0 =C2=A0 =C2=A0 =C2=A0 Title=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0:= The memory-hard Argon2 password hash and proof-of-work function
=C2=A0 =C2=A0 =C2=A0 =C2=A0 Authors=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0: Alex= Biryukov
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 Daniel Dinu
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 Dmitry Khovratovich
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 Simon Josefsson
=C2=A0 =C2=A0 =C2=A0 =C2=A0 Filename=C2=A0 =C2=A0 =C2=A0 =C2=A0 : draft-irt= f-cfrg-argon2-02.txt
=C2=A0 =C2=A0 =C2=A0 =C2=A0 Pages=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0:= 26
=C2=A0 =C2=A0 =C2=A0 =C2=A0 Date=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 := 2017-03-27

Abstract:
=C2=A0 =C2=A0This document describes the Argon2 memory-hard function for pa= ssword
=C2=A0 =C2=A0hashing and proof-of-work applications.=C2=A0 We provide an im= plementer
=C2=A0 =C2=A0oriented description together with sample code and test vector= s.=C2=A0 The
=C2=A0 =C2=A0purpose is to simplify adoption of Argon2 for Internet protoco= ls.


The IETF datatracker status page for this draft is:
https://datatracker.ietf.org/doc/draft-= irtf-cfrg-argon2/

There are also htmlized versions available at:
https://tools.ietf.org/html/draft-irtf-cfr= g-argon2-02
https://datatracker.ietf.org/doc= /html/draft-irtf-cfrg-argon2-02

A diff from the previous version is available at:
https://www.ietf.org/rfcdiff?url2= =3Ddraft-irtf-cfrg-argon2-02


Please note that it may take a couple of minutes from the time of submissio= n
until the htmlized version and diff are available at tools.ietf.org.

Internet-Drafts are also available by anonymous FTP at:
ftp://ftp.ietf.org/internet-drafts/

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https://www.irtf.org/mailman/listinfo/cfrg



--
Best regards,<= /div>
Dmitry Khovratovich
--001a113ea1465d10b2054bb4201b--