Subject: Diffie-Hellman DomainParameters question

From: "william bamberg" <[email-masked]>
Date: Tue, 22 Feb 2000 16:10:44 -0000

RFC 2459, and the new draft, both specify the DomainParameters to be
included along with a D-H public key value with the following syntax:

        DomainParameters ::= SEQUENCE {
              p       INTEGER, -- odd prime, p=jq +1
              g       INTEGER, -- generator, g
              q       INTEGER, -- factor of p-1
              j       INTEGER OPTIONAL, -- subgroup factor
              validationParms  ValidationParms OPTIONAL }

I'm not a crypto expert, but I understand that the q value is not actually
essential for doing Diffie-Hellman, and most D-H certificates that I've come
across seem to omit it. Could anyone explain to me why it's not optional in
the spec?

Thanks very much

Will

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From: Russ Housley <[email-masked]>
Date: Tue, 22 Feb 2000 22:36:58 -0500

Will:

Two reasons, one political and one technical.

1.  This structure is aligned with the ANSI X9.42 standard.  The banking 
community and the Internet community will be using the same structure.

2.  The value of q is needed to avoid some small subgroup attacks.  See 
draft-ietf-smime-small-subgroup-03.txt.

Russ