NAME

       DSA_generate_parameters - generate DSA parameters

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

       dsa(3), ERR_get_error(3), 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.