Choice of strong primes for Photuris

[Phil Karn <karn@unix.ka9q.ampr.org>]

Colin Plumb, who did much of the modular exponentiation code for PGP,
has recently developed a fast algorithm for the special case when the
base is 2. This speeds up one part of Diffie-Hellman, the
precomputation of the public component from the private component (but
not the computation of the actual session key).

The strong prime currently in the Photuris draft has generator 5.  To
accomodate Colin's work I'm going to change to another 1024-bit strong
prime with a generator of 2. I'd already generated several strong
primes with generators of 2, but not having any reason to prefer one
over another I originally chose another one at random.

As far as anyone knows, all these generator/prime pairs are equally
secure, but of course if anyone has heard anything to the contrary I
would like to know.

Phil

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