DSA_generate_parameters(3)

NAME
DSA_generate_parameters - generate DSA parameters

LIBRARY
libcrypto, -lcrypto

SYNOPSIS
 #include <openssl/dsa.h>

 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() generates primes p and q and a generator g for use in the 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() 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 callback is not NULL, it will be called as follows:

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

•   When a candidate for q has passed a test by trial division, callback(1, -1, cb_arg) is called. While a candidate for q is tested by Miller-Rabin primality tests, callback(1, i, cb_arg) 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, callback(2, 0, cb_arg) and callback(3, 0, cb_arg) are called.

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

•   When a candidate for p has passed the test by trial division, callback(1, -1, cb_arg) is called. While it is tested by the Miller-Rabin primality test, callback(1, i, cb_arg) 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, callback(2, 1, cb_arg) is called.

•   When the generator has been found, callback(3, 1, cb_arg) is called.

RETURN VALUE
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).

BUGS
Seed lengths > 20 are not supported.

SEE ALSO
openssl_dsa(3), ERR_get_error(3), openssl_rand(3), DSA_free(3)

HISTORY
DSA_generate_parameters() appeared in SSLeay 0.8. The cb_arg argument was added in SSLeay 0.9.0. 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.