Snort's "sfhashfcn" function and parameters

I've been reading the source for the algorithm Snort uses to calculate
hashes of session keys. I'm curious about the rationale for the three
values chosen to parameterise it.

If sfhashfcn_static is used, we have:

seed     = 3193;
scale    = 719;
hardener = 133824503;

If not:

seed     = sf_nearest_prime( (rand()%m)+3191 );
scale    = sf_nearest_prime( (rand()%m)+709 );
hardener = (rand()*rand()) + 133824503;

I'm curious about the values, but in particular about a discrepancy between
the static and non-static values. In the non-static case, seed and scale
have to be prime numbers (and I'd be quite pleased if someone could explain
why!). In the static case, however, seed is a composite:

(3193 = 31 x 103)

James McLaughlin.

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