=pod

=head1 NAME

DSA_generate_parameters - Generate DSA parameters

=head1 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)(), void *cb_arg);

=head1 DESCRIPTION

DSA_generate_parameters() generates primes p and q and a generator g
for use in the DSA.

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

If B<seed> is NULL or B<seed_len> E<lt> 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 B<seed>.

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

A callback function may be used to provide feedback about the progress
of the key generation. If B<callback> is not B<NULL>, it will be
called as follows:

=over 4

=item *

When the the m-th candidate for q is generated, B<callback(0, m,
cb_arg)> is called.

=item *

B<callback(1, j++, cb_arg)> is called in the inner loop of the
Miller-Rabin primality test.

=item *

When a prime q has been found, B<callback(2, 0, cb_arg)> and
B<callback(3, 0, cb_arg)> are called.

=item *

While candidates for p are being tested, B<callback(1, j++, cb_arg)>
is called in the inner loop of the Miller-Rabin primality test, then
B<callback(0, counter, cb_arg)> is called when the next candidate
is chosen.

=item *

When p has been found, B<callback(2, 1, cb_arg)> is called.

=item *

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

=back

=head1 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 L<ERR_get_error(3)|ERR_get_error(3)>.

=head1 BUGS

The deterministic generation of p does not follow the NIST algorithm:
r0 is SHA1(s+k+1), but should be SHA1(s+j+k) with j_0=2,
j_counter=j_counter-1 + n + 1.

Seed lengths E<gt> 20 are not supported.

=head1 SEE ALSO

L<dsa(3)|dsa(3)>, L<err(3)|err(3)>, L<rand(3)|rand(3)>,
L<DSA_free(3)|DSA_free(3)>

=head1 HISTORY

DSA_generate_parameters() appeared in SSLeay 0.8. The B<cb_arg>
argument was added in SSLeay 0.9.0.

=cut
