questions on RFC2631 and DH key agreement

[Hal Finney]

Jeff Hodges wrote:
> Thanks for your thoughts on this Hal. Quite educational. 
>
> > Jeff Hodges wrote:
> > > It turns out the supplied default for p is 1024 bit -- I'd previously goofed 
> > > when using wc on it..
> > >
> > > DCF93A0B883972EC0E19989AC5A2CE310E1D37717E8D9571BB7623731866E61EF75A2E27898B057
> > > F9891C2E27A639C3F29B60814581CD3B2CA3986D2683705577D45C2E7E52DC81C7A171876E5CEA7
> > > 4B1448BFDFAF18828EFD2519F14E45E3826634AF1949E5B535CC829A483B8A76223E5D490A257F0
> > > 5BDFF16F2FB22C583AB
> > 
> > This p is a "strong" prime, one where (p-1)/2 is also a prime, a good
> > property for a DH modulus.
>
> Ok, so what tools did you use to ascertain that? I'm curious. 

I copied and pasted it into Python as p, set p1 = (p-1)/2, and did
pow(2L,p1-1,p1), pow(3L,p1-1,p1) and a few such Fermat tests, always
getting 1 as the result, to confirm that p1 is prime. I then did
pow(2L,p1,p) and got p-1 rather than 1, which tells me that 2 generates
the whole group rather than the subgroup of order p1.

Hal

---------------------------------------------------------------------
The Cryptography Mailing List
Unsubscribe by sending "unsubscribe cryptography" to majordomo at metzdowd.com