Re: [IPsec] Question about RFC 5114

"Dan Harkins" <dharkins@lounge.org> Fri, 26 March 2010 23:55 UTC

Return-Path: <dharkins@lounge.org>
X-Original-To: ipsec@core3.amsl.com
Delivered-To: ipsec@core3.amsl.com
Received: from localhost (localhost [127.0.0.1]) by core3.amsl.com (Postfix) with ESMTP id 41B413A6A7D for <ipsec@core3.amsl.com>; Fri, 26 Mar 2010 16:55:32 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -4.697
X-Spam-Level:
X-Spam-Status: No, score=-4.697 tagged_above=-999 required=5 tests=[AWL=0.438, BAYES_00=-2.599, DNS_FROM_OPENWHOIS=1.13, IP_NOT_FRIENDLY=0.334, RCVD_IN_DNSWL_MED=-4]
Received: from mail.ietf.org ([64.170.98.32]) by localhost (core3.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id rN6TEMW3mVrw for <ipsec@core3.amsl.com>; Fri, 26 Mar 2010 16:55:31 -0700 (PDT)
Received: from colo.trepanning.net (colo.trepanning.net [69.55.226.174]) by core3.amsl.com (Postfix) with ESMTP id 539113A683C for <ipsec@ietf.org>; Fri, 26 Mar 2010 16:55:31 -0700 (PDT)
Received: from www.trepanning.net (localhost [127.0.0.1]) by colo.trepanning.net (Postfix) with ESMTP id 386BE1022404A; Fri, 26 Mar 2010 16:55:55 -0700 (PDT)
Received: from 69.12.173.8 (SquirrelMail authenticated user dharkins@lounge.org) by www.trepanning.net with HTTP; Fri, 26 Mar 2010 16:55:55 -0700 (PDT)
Message-ID: <246830bbd70485253e0824df38f2fda5.squirrel@www.trepanning.net>
In-Reply-To: <1269638701.2838.303.camel@faith.austin.ibm.com>
References: <1269638701.2838.303.camel@faith.austin.ibm.com>
Date: Fri, 26 Mar 2010 16:55:55 -0700 (PDT)
From: "Dan Harkins" <dharkins@lounge.org>
To: latten@austin.ibm.com
User-Agent: SquirrelMail/1.4.14 [SVN]
MIME-Version: 1.0
Content-Type: text/plain;charset=iso-8859-1
Content-Transfer-Encoding: 8bit
X-Priority: 3 (Normal)
Importance: Normal
Cc: ipsec@ietf.org, avagarwa@redhat.com, kent@bbn.com, mlepinski@bbn.com
Subject: Re: [IPsec] Question about RFC 5114
X-BeenThere: ipsec@ietf.org
X-Mailman-Version: 2.1.9
Precedence: list
List-Id: Discussion of IPsec protocols <ipsec.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/listinfo/ipsec>, <mailto:ipsec-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/ipsec>
List-Post: <mailto:ipsec@ietf.org>
List-Help: <mailto:ipsec-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/ipsec>, <mailto:ipsec-request@ietf.org?subject=subscribe>
X-List-Received-Date: Fri, 26 Mar 2010 23:55:32 -0000

  Hi Joy,

  "q" is the order of the group defined by the "g". If you want to use
the FIPS 186-3 process for generating a D-H key pair with the other MODP
groups that don't have a defined order (like 5, 14, 15, 16...) you can
just use (p-1/2) for the value "q".

  There are going to be q distinct elements in the group and while
D-H will work with a private value x: q < x < p, you will be doing more
modular exponentiation. The FIPS 186-3 process is ensuring that your
private value, x, will be taken from a uniformly random distribution of
numbers less than q and therefore the public value y=g^x mod p will be
a random element in the group (which is what you need for D-H).

  regards,

  Dan.

On Fri, March 26, 2010 2:25 pm, Joy Latten wrote:
> Hi,
>
> I am looking to implement modp groups 22, 23, and 24 into IKE but have a
> question.
>
> RFC 5114 gives the prime, p, the generator, g and a subgroup, q, with a
> specific size...
>
> Because prior rfcs for modp groups did not specify a "q", I was not sure
> if this was a new constant or just stating a size requirement?
> So I took a look at NIST 800-56A. In particular,
>
> 5.6.1 Private/Public Key Pair Generation
>
> 5.6.1.1 FFC Key Pair Generation
> For the FFC schemes, each static and ephemeral private key and public
> key shall be generated using an Approved method and the selected valid
> domain parameters (p, q, g{, SEED,pgenCounter}) (see Appendix B of FIPS
> 186-3).
> ...
>
> I then took a look at FIPS 186-3, Appendix B, which documents 2 methods
> for finite field cryptography (FFC) key pair generation.
> For example, one method is "Key Pair Generation Using Extra Random
> Bits". It actually states that "q" is an input and it is used to do an
> additional computation to compute "x".
>
> I am somewhat confused, are the modp groups 22, 23 & 24 suppose to use
> one of these new methods and that is why "q" is given in rfc 5114?
> Or am I to ignore this and just continue with existing way
> where "q" is not used and there aren't any additional computations
> to compute x.
>
> I am not even sure this is correct place to ask, but any advice
> would be welcome.
>
> regards,
> Joy
>
>
> (Cut-n-paste from FIPs 186-3 below to show input and process)
>
>  Input:
>     (p, q, g)      The subset of the domain parameters that are used
>                    for this process. p, q and g shall either be
>                    provided as integers during input, or shall be
>                    converted to integers prior to use.
>
> Process:
> 1. N = len(q); L = len(p).    Comment: Check that the (L, N) pair
>                               is specified in Section 4.2.
> 2. If the (L, N) pair is invalid, then return an ERROR indicator,
>    Invalid_x, and Invalid_y.
> 3. requested_security_strength = the security strength associated
>    with the (L, N) pair;      see SP 800-57.
> 4. Obtain a string of N+64 returned_bits from an RBG with a security
>    strength of requested_security_strength or more. If an ERROR
>    indication is returned, then return an ERROR indication,
>    Invalid_x, and Invalid_y.
> 5. Convert returned_bits to the (non-negative) integer c (see
>    Appendix C.2.1).
> 6. x = (c mod (q–1)) + 1.       Comment: 0 ≤ c mod (q–1) ≤ q–2
> and
>                                 implies that 1 ≤ x ≤ q–1.
> 7. y = gx mod p.
> 8. Return SUCCESS, x, and y.
>
> _______________________________________________
> IPsec mailing list
> IPsec@ietf.org
> https://www.ietf.org/mailman/listinfo/ipsec
>