1=pod 2 3=head1 NAME 4 5DSA_generate_parameters - generate DSA parameters 6 7=head1 SYNOPSIS 8 9 #include <openssl/dsa.h> 10 11 DSA *DSA_generate_parameters(int bits, unsigned char *seed, 12 int seed_len, int *counter_ret, unsigned long *h_ret, 13 void (*callback)(int, int, void *), void *cb_arg); 14 15=head1 DESCRIPTION 16 17DSA_generate_parameters() generates primes p and q and a generator g 18for use in the DSA. 19 20B<bits> is the length of the prime to be generated; the DSS allows a 21maximum of 1024 bits. 22 23If B<seed> is B<NULL> or B<seed_len> E<lt> 20, the primes will be 24generated at random. Otherwise, the seed is used to generate 25them. If the given seed does not yield a prime q, a new random 26seed is chosen and placed at B<seed>. 27 28DSA_generate_parameters() places the iteration count in 29*B<counter_ret> and a counter used for finding a generator in 30*B<h_ret>, unless these are B<NULL>. 31 32A callback function may be used to provide feedback about the progress 33of the key generation. If B<callback> is not B<NULL>, it will be 34called as follows: 35 36=over 4 37 38=item * 39 40When a candidate for q is generated, B<callback(0, m++, cb_arg)> is called 41(m is 0 for the first candidate). 42 43=item * 44 45When a candidate for q has passed a test by trial division, 46B<callback(1, -1, cb_arg)> is called. 47While a candidate for q is tested by Miller-Rabin primality tests, 48B<callback(1, i, cb_arg)> is called in the outer loop 49(once for each witness that confirms that the candidate may be prime); 50i is the loop counter (starting at 0). 51 52=item * 53 54When a prime q has been found, B<callback(2, 0, cb_arg)> and 55B<callback(3, 0, cb_arg)> are called. 56 57=item * 58 59Before a candidate for p (other than the first) is generated and tested, 60B<callback(0, counter, cb_arg)> is called. 61 62=item * 63 64When a candidate for p has passed the test by trial division, 65B<callback(1, -1, cb_arg)> is called. 66While it is tested by the Miller-Rabin primality test, 67B<callback(1, i, cb_arg)> is called in the outer loop 68(once for each witness that confirms that the candidate may be prime). 69i is the loop counter (starting at 0). 70 71=item * 72 73When p has been found, B<callback(2, 1, cb_arg)> is called. 74 75=item * 76 77When the generator has been found, B<callback(3, 1, cb_arg)> is called. 78 79=back 80 81=head1 RETURN VALUE 82 83DSA_generate_parameters() returns a pointer to the DSA structure, or 84B<NULL> if the parameter generation fails. The error codes can be 85obtained by L<ERR_get_error(3)|ERR_get_error(3)>. 86 87=head1 BUGS 88 89Seed lengths E<gt> 20 are not supported. 90 91=head1 SEE ALSO 92 93L<dsa(3)|dsa(3)>, L<ERR_get_error(3)|ERR_get_error(3)>, L<rand(3)|rand(3)>, 94L<DSA_free(3)|DSA_free(3)> 95 96=head1 HISTORY 97 98DSA_generate_parameters() appeared in SSLeay 0.8. The B<cb_arg> 99argument was added in SSLeay 0.9.0. 100In versions up to OpenSSL 0.9.4, B<callback(1, ...)> was called 101in the inner loop of the Miller-Rabin test whenever it reached the 102squaring step (the parameters to B<callback> did not reveal how many 103witnesses had been tested); since OpenSSL 0.9.5, B<callback(1, ...)> 104is called as in BN_is_prime(3), i.e. once for each witness. 105=cut 106