Re: [IPsec] Question about RFC 5114
"Dan Harkins" <dharkins@lounge.org> Fri, 26 March 2010 23:55 UTC
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Date: Fri, 26 Mar 2010 16:55:55 -0700
From: Dan Harkins <dharkins@lounge.org>
To: latten@austin.ibm.com
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Cc: ipsec@ietf.org, avagarwa@redhat.com, kent@bbn.com, mlepinski@bbn.com
Subject: Re: [IPsec] Question about RFC 5114
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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 (qâ1)) + 1. Comment: 0 ⤠c mod (qâ1) ⤠qâ2 > and > implies that 1 ⤠x ⤠qâ1. > 7. y = gx mod p. > 8. Return SUCCESS, x, and y. > > _______________________________________________ > IPsec mailing list > IPsec@ietf.org > https://www.ietf.org/mailman/listinfo/ipsec >
- [IPsec] Question about RFC 5114 Joy Latten
- Re: [IPsec] Question about RFC 5114 Kaz Kobara
- Re: [IPsec] Question about RFC 5114 Dan Harkins
- Re: [IPsec] Question about RFC 5114 Scott Fluhrer (sfluhrer)
- Re: [IPsec] Question about RFC 5114 Kaz Kobara
- Re: [IPsec] Question about RFC 5114 Scott Fluhrer (sfluhrer)
- Re: [IPsec] Question about RFC 5114 Joy Latten
- Re: [IPsec] Question about RFC 5114 Richard Barnes
- Re: [IPsec] Question about RFC 5114 Joy Latten