BN_generate_prime_ex() generates a pseudo-random prime number of
at least bit length B<bits>. The returned number is probably prime
-with a negligible error.
+with a negligible error. If B<add> is B<NULL> the returned prime
+number will have exact bit length B<bits> with the top most two
+bits set.
If B<ret> is not B<NULL>, it will be used to store the number.
generator.
If B<safe> is true, it will be a safe prime (i.e. a prime p so
-that (p-1)/2 is also prime).
+that (p-1)/2 is also prime). If B<safe> is true, and B<rem> == B<NULL>
+the condition will be p % B<add> == 3.
+It is recommended that B<add> is a multiple of 4.
The random generator must be seeded prior to calling BN_generate_prime_ex().
If the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to