DSA_GENERATE_PARAMETERS_EX(3)

NAME
DSA_generate_parameters_ex - generate DSA parameters

SYNOPSIS
libcrypto
#include <openssl/dsa.h>
int
DSA_generate_parameters_ex(DSA *dsa, int bits, const unsigned char *seed, int seed_len, int *counter_ret, unsigned long *h_ret, BN_GENCB *cb);

DESCRIPTION
DSA_generate_parameters_ex() generates primes p and q and a generator g for use in the DSA and stores the result in dsa.

bits is the length of the prime to be generated; the DSS allows a maximum of 1024 bits.

If seed is NULL or seed_len < 20, the primes will be generated at random. Otherwise, the seed is used to generate them. If the given seed does not yield a prime q, a new random seed is chosen and placed at seed.

DSA_generate_parameters_ex() places the iteration count in *counter_ret and a counter used for finding a generator in *h_ret, unless these are NULL.

A callback function may be used to provide feedback about the progress of the key generation. If cb is not NULL, it will be called as shown below. For information on the BN_GENCB structure, refer to BN_GENCB_call(3).

•   When a candidate for q is generated, BN_GENCB_call(cb, 0, m++) is called (m is 0 for the first candidate).

•   When a candidate for q has passed a test by trial division, BN_GENCB_call(cb, 1, -1) is called. While a candidate for q is tested by Miller-Rabin primality tests, BN_GENCB_call(cb, 1, i) is called in the outer loop (once for each witness that confirms that the candidate may be prime); i is the loop counter (starting at 0).

•   When a prime q has been found, BN_GENCB_call(cb, 2, 0) and BN_GENCB_call(cb, 3, 0) are called.

•   Before a candidate for p (other than the first) is generated and tested, BN_GENCB_call(cb, 0, counter) is called.

•   When a candidate for p has passed the test by trial division, BN_GENCB_call(cb, 1, -1) is called. While it is tested by the Miller-Rabin primality test, BN_GENCB_call(cb, 1, i) is called in the outer loop (once for each witness that confirms that the candidate may be prime). i is the loop counter (starting at 0).

•   When p has been found, BN_GENCB_call(cb, 2, 1) is called.

•   When the generator has been found, BN_GENCB_call(cb, 3, 1) is called.

RETURN VALUES
DSA_generate_parameters_ex() returns a 1 on success, or 0 otherwise.

The error codes can be obtained by ERR_get_error(3).

SEE ALSO
BN_generate_prime(3), DSA_get0_pqg(3), DSA_new(3)

HISTORY
DSA_generate_parameters_ex() first appeared in OpenSSL 0.9.8 and has been available since OpenBSD 4.5.

BUGS
Seed lengths > 20 are not supported.