is true, it will be a safe prime (i.e. a prime p so
that (p-1)/2 is also prime).
The PRNG must be seeded prior to calling BN_generate_prime_ex().
The prime number generation has a negligible error probability.
BN_is_prime_ex() and BN_is_prime_fasttest_ex() test if the number B is
prime. The following tests are performed until one of them shows that
B

is composite; if B

passes all these tests, it is considered
prime.
BN_is_prime_fasttest_ex(), when called with B,
first attempts trial division by a number of small primes;
if no divisors are found by this test and B is not B,
B is called.
If B, this test is skipped.
Both BN_is_prime_ex() and BN_is_prime_fasttest_ex() perform a Miller-Rabin
probabilistic primality test with B iterations. If
B, a number of iterations is used that
yields a false positive rate of at most 2^-80 for random input.
If B is not B, B is called
after the j-th iteration (j = 0, 1, ...). B is a
pre-allocated B (to save the overhead of allocating and
freeing the structure in a loop), or B.
BN_GENCB_call calls the callback function held in the B structure
and passes the ints B and B** as arguments. There are two types of
B structure that are supported: "new" style and "old" style. New
programs should prefer the "new" style, whilst the "old" style is provided
for backwards compatibility purposes.
A BN_GENCB structure should be created through a call to BN_GENCB_new, and freed
through a call to BN_GENCB_free.
For "new" style callbacks a BN_GENCB structure should be initialised with a
call to BN_GENCB_set(), where B is a B, B is of
type B and B is a B.
"Old" style callbacks are the same except they are initialised with a call
to BN_GENCB_set_old() and B is of type
B.
A callback is invoked through a call to B. This will check
the type of the callback and will invoke B for new
style callbacks or B for old style.
It is possible to obtained the argument associated with a BN_GENCB structure
(set via a call to BN_GENCB_set or BN_GENCB_set_old) using BN_GENCB_get_arg.
BN_generate_prime (deprecated) works in the same way as
BN_generate_prime_ex but expects an old style callback function
directly in the B parameter, and an argument to pass to it in
the B. Similarly BN_is_prime and BN_is_prime_fasttest are
deprecated and can be compared to BN_is_prime_ex and
BN_is_prime_fasttest_ex respectively.
=head1 RETURN VALUES
BN_generate_prime_ex() return 1 on success or 0 on error.
BN_is_prime_ex(), BN_is_prime_fasttest_ex(), BN_is_prime() and
BN_is_prime_fasttest() return 0 if the number is composite, 1 if it is
prime with an error probability of less than 0.25^B, and
-1 on error.
BN_generate_prime() returns the prime number on success, B otherwise.
BN_GENCB_new returns a pointer to a BN_GENCB structure on success, or B
otherwise.
BN_GENCB_get_arg returns the argument previously associated with a BN_GENCB
structure.
Callback functions should return 1 on success or 0 on error.
The error codes can be obtained by L.
=head1 REMOVED FUNCTIONALITY
As of OpenSSL 1.1.0 it is no longer possible to create a BN_GENCB structure
directly, as in:
BN_GENCB callback;
Instead applications should create a BN_GENCB structure using BN_GENCB_new:
BN_GENCB *callback;
callback = BN_GENCB_new();
if(!callback) /* handle error */
...
BN_GENCB_free(callback);
=head1 SEE ALSO
L, L, L
=head1 HISTORY
The B arguments to BN_generate_prime() and to BN_is_prime()
were added in SSLeay 0.9.0. The B argument to BN_generate_prime()
was added in SSLeay 0.9.1.
BN_is_prime_fasttest() was added in OpenSSL 0.9.5. BN_GENCB_new, BN_GENCB_free
and BN_GENCB_get_arg were added in OpenSSL 1.1.0
=cut
**