# RedHat 9 (Linux i386) - man page for bn_is_prime (redhat section 3)

BN_generate_prime(3) OpenSSL BN_generate_prime(3)BN_generate_prime, BN_is_prime, BN_is_prime_fasttest - generate primes and test for primalityNAME#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);SYNOPSISBN_generate_prime() generates a pseudo-random 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: o callback(0, i, cb_arg) is called after generating the i-th potential prime number. o While the number is being tested for primality, callback(1, j, cb_arg) is called as described below. o When a prime has been found, callback(2, i, cb_arg) is called. The prime may have to fulfill additional requirements for use in Diffie-Hellman 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 (p-1)/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,DESCRIPTION, cb_arg) is called. If do_trial_division == 0, this test is skipped. Both BN_is_prime() and BN_is_prime_fasttest() perform a Miller-Rabin probabilistic primality test with checks iterations. If checks == BN_prime_checks, 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 j-th iteration (j = 0, 1, ...). ctx is a pre-allocated BN_CTX (to save the overhead of allocating and freeing the structure in a loop), or NULL.-1BN_generate_prime() returns the prime number on success, NULL otherwise. BN_is_prime() returns 0 if the number is composite, 1 if it is prime with an error probability of less than 0.25^checks, andRETURN VALUESon error. The error codes can be obtained by ERR_get_error(3).-1bn(3), ERR_get_error(3), rand(3)SEE ALSOThe 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. BN_is_prime_fasttest() was added in OpenSSL 0.9.5.HISTORY0.9.7a2003-01-13 BN_generate_prime(3)