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. The generator g=2 generates the entire group,
which is an OK choice. It means that one bit of the shared secret is
leaked (whether or not it is a quadratic residue, i.e. whether the
discrete log of the number is even or odd). But that shouldn't matter,
the shared secret should be hashed and/or used as the seed of a PRNG to
generate further keys.

The main problem as I said is that 1024 bit moduli are no longer
considered sufficiently safe for more than casual purposes. Particularly
with discrete logs that use a widely-shared modulus like the one above,
it would not be surprising to see it publicly broken in the next 5-10
years, or perhaps even sooner. And if a public effort can accomplish it
in a few years, conservatively we should assume that well funded secret
efforts could already succeed today.

Hal Finney

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