
BN_generate_prime(3)
Contents

BN_generate_prime, BN_is_prime, BN_is_prime_fasttest 
Generate primes and test for primality
#include <openssl/bn.h>
BIGNUM *BN_generate_prime(
BIGNUM *ret, int num, int safe, BIGNUM *add,
BIGNUM *rem, void (*callback)(int, int, void *), void
*cb_arg ); int BN_is_prime(
const BIGNUM *a, int checks, void (*callback)(int,
int, void *), BN_CTX *ctx, void *cb_arg ); int
BN_is_prime_fasttest(
const BIGNUM *a, int checks, void (*callback)(int,
int, void *), BN_CTX *ctx, void *cb_arg, int
do_trial_division );
The BN_generate_prime() function generates a pseudorandom
prime number of num bits. If ret is not NULL, it will be
used to store the number.
If callback is not NULL, it is called as follows: callback(0,
i, cb_arg) is called after generating the ith
potential prime number. While the number is being tested
for primality, callback(1, j, cb_arg) is called as
described below. When a prime has been found, callback(2,
i, cb_arg) is called.
The prime may have to fulfill additional requirements for
use in DiffieHellman key exchange:
If add is not NULL, the prime will fulfill the condition p
% add == rem (p % add == 1 if rem == NULL) in order to
suit a given generator.
If safe is true, it will be a safe prime (i.e. a prime p
so that (p1)/2 is also prime).
The PRNG must be seeded prior to calling BN_generate_prime().
The prime number generation has a negligible
error probability.
BN_is_prime() and BN_is_prime_fasttest() test if the number
a is prime. The following tests are performed until
one of them shows that a is composite; if a passes all
these tests, it is considered prime.
BN_is_prime_fasttest(), when called with do_trial_division
== 1, first attempts trial division by a number of small
primes; if no divisors are found by this test and callback
is not NULL, callback(1, 1, cb_arg) is called. If
do_trial_division == 0, this test is skipped.
Both BN_is_prime() and BN_is_prime_fasttest() perform a
MillerRabin probabilistic primality test with checks
iterations. If checks == BN_prime_check, a number of iterations
is used that yields a false positive rate of at
most 2^80 for random input.
If callback is not NULL, callback(1, j, cb_arg) is called
after the jth iteration (j = 0, 1, ...). ctx is a preallocated
BN_CTX (to save the overhead of allocating and
freeing the structure in a loop), or NULL.
The BN_generate_prime() function returns the prime number
on success, NULL otherwise.
The BN_is_prime() function returns 0 if the number is composite,
1 if it is prime with an error probability of less
than 0.25^checks, and 1 on error.
The error codes can be obtained by using the
ERR_get_error() function.
The cb_arg arguments to BN_generate_prime() and to
BN_is_prime() were added in SSLeay 0.9.0. The ret argument
to BN_generate_prime() was added in SSLeay 0.9.1. The
BN_is_prime_fasttest() function was added in OpenSSL
0.9.5.
Functions: bn(3), err(3), rand(3)
BN_generate_prime(3)
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