DSA_GENERATE_PARAMETERS(3)

NAME
DSA_generate_parameters_ex, DSA_generate_parameters - generate DSA parameters

SYNOPSIS
#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);

Deprecated:

DSA *
DSA_generate_parameters(int bits, unsigned char *seed, int seed_len, int *counter_ret, unsigned long *h_ret, void (*callback)(int, int, void *), void *cb_arg);

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.

DSA_generate_parameters() (deprecated) works in much the same way as for DSA_generate_parameters_ex(), except that no dsa parameter is passed and instead a newly allocated DSA structure is returned. Additionally "old style" callbacks are used instead of the newer BN_GENCB based approach. Refer to BN_generate_prime(3) for further information.

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

DSA_generate_parameters() returns a pointer to the DSA structure, or NULL if the parameter generation fails.

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

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

HISTORY
DSA_generate_parameters() first appeared in SSLeay 0.8.0 and had its cb_arg argument added in SSLeay 0.9.0. It has been available since OpenBSD 2.4.

In versions up to OpenSSL 0.9.4, callback(1, ...) was called in the inner loop of the Miller-Rabin test whenever it reached the squaring step (the parameters to callback() did not reveal how many witnesses had been tested); since OpenSSL 0.9.5, callback(1, ...) is called as in BN_is_prime(3), i.e. once for each witness.

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.