1*2175Sjp161948=pod
2*2175Sjp161948
3*2175Sjp161948=head1 NAME
4*2175Sjp161948
5*2175Sjp161948DSA_generate_parameters - generate DSA parameters
6*2175Sjp161948
7*2175Sjp161948=head1 SYNOPSIS
8*2175Sjp161948
9*2175Sjp161948 #include <openssl/dsa.h>
10*2175Sjp161948
11*2175Sjp161948 DSA *DSA_generate_parameters(int bits, unsigned char *seed,
12*2175Sjp161948                int seed_len, int *counter_ret, unsigned long *h_ret,
13*2175Sjp161948		void (*callback)(int, int, void *), void *cb_arg);
14*2175Sjp161948
15*2175Sjp161948=head1 DESCRIPTION
16*2175Sjp161948
17*2175Sjp161948DSA_generate_parameters() generates primes p and q and a generator g
18*2175Sjp161948for use in the DSA.
19*2175Sjp161948
20*2175Sjp161948B<bits> is the length of the prime to be generated; the DSS allows a
21*2175Sjp161948maximum of 1024 bits.
22*2175Sjp161948
23*2175Sjp161948If B<seed> is B<NULL> or B<seed_len> E<lt> 20, the primes will be
24*2175Sjp161948generated at random. Otherwise, the seed is used to generate
25*2175Sjp161948them. If the given seed does not yield a prime q, a new random
26*2175Sjp161948seed is chosen and placed at B<seed>.
27*2175Sjp161948
28*2175Sjp161948DSA_generate_parameters() places the iteration count in
29*2175Sjp161948*B<counter_ret> and a counter used for finding a generator in
30*2175Sjp161948*B<h_ret>, unless these are B<NULL>.
31*2175Sjp161948
32*2175Sjp161948A callback function may be used to provide feedback about the progress
33*2175Sjp161948of the key generation. If B<callback> is not B<NULL>, it will be
34*2175Sjp161948called as follows:
35*2175Sjp161948
36*2175Sjp161948=over 4
37*2175Sjp161948
38*2175Sjp161948=item *
39*2175Sjp161948
40*2175Sjp161948When a candidate for q is generated, B<callback(0, m++, cb_arg)> is called
41*2175Sjp161948(m is 0 for the first candidate).
42*2175Sjp161948
43*2175Sjp161948=item *
44*2175Sjp161948
45*2175Sjp161948When a candidate for q has passed a test by trial division,
46*2175Sjp161948B<callback(1, -1, cb_arg)> is called.
47*2175Sjp161948While a candidate for q is tested by Miller-Rabin primality tests,
48*2175Sjp161948B<callback(1, i, cb_arg)> is called in the outer loop
49*2175Sjp161948(once for each witness that confirms that the candidate may be prime);
50*2175Sjp161948i is the loop counter (starting at 0).
51*2175Sjp161948
52*2175Sjp161948=item *
53*2175Sjp161948
54*2175Sjp161948When a prime q has been found, B<callback(2, 0, cb_arg)> and
55*2175Sjp161948B<callback(3, 0, cb_arg)> are called.
56*2175Sjp161948
57*2175Sjp161948=item *
58*2175Sjp161948
59*2175Sjp161948Before a candidate for p (other than the first) is generated and tested,
60*2175Sjp161948B<callback(0, counter, cb_arg)> is called.
61*2175Sjp161948
62*2175Sjp161948=item *
63*2175Sjp161948
64*2175Sjp161948When a candidate for p has passed the test by trial division,
65*2175Sjp161948B<callback(1, -1, cb_arg)> is called.
66*2175Sjp161948While it is tested by the Miller-Rabin primality test,
67*2175Sjp161948B<callback(1, i, cb_arg)> is called in the outer loop
68*2175Sjp161948(once for each witness that confirms that the candidate may be prime).
69*2175Sjp161948i is the loop counter (starting at 0).
70*2175Sjp161948
71*2175Sjp161948=item *
72*2175Sjp161948
73*2175Sjp161948When p has been found, B<callback(2, 1, cb_arg)> is called.
74*2175Sjp161948
75*2175Sjp161948=item *
76*2175Sjp161948
77*2175Sjp161948When the generator has been found, B<callback(3, 1, cb_arg)> is called.
78*2175Sjp161948
79*2175Sjp161948=back
80*2175Sjp161948
81*2175Sjp161948=head1 RETURN VALUE
82*2175Sjp161948
83*2175Sjp161948DSA_generate_parameters() returns a pointer to the DSA structure, or
84*2175Sjp161948B<NULL> if the parameter generation fails. The error codes can be
85*2175Sjp161948obtained by L<ERR_get_error(3)|ERR_get_error(3)>.
86*2175Sjp161948
87*2175Sjp161948=head1 BUGS
88*2175Sjp161948
89*2175Sjp161948Seed lengths E<gt> 20 are not supported.
90*2175Sjp161948
91*2175Sjp161948=head1 SEE ALSO
92*2175Sjp161948
93*2175Sjp161948L<dsa(3)|dsa(3)>, L<ERR_get_error(3)|ERR_get_error(3)>, L<rand(3)|rand(3)>,
94*2175Sjp161948L<DSA_free(3)|DSA_free(3)>
95*2175Sjp161948
96*2175Sjp161948=head1 HISTORY
97*2175Sjp161948
98*2175Sjp161948DSA_generate_parameters() appeared in SSLeay 0.8. The B<cb_arg>
99*2175Sjp161948argument was added in SSLeay 0.9.0.
100*2175Sjp161948In versions up to OpenSSL 0.9.4, B<callback(1, ...)> was called
101*2175Sjp161948in the inner loop of the Miller-Rabin test whenever it reached the
102*2175Sjp161948squaring step (the parameters to B<callback> did not reveal how many
103*2175Sjp161948witnesses had been tested); since OpenSSL 0.9.5, B<callback(1, ...)>
104*2175Sjp161948is called as in BN_is_prime(3), i.e. once for each witness.
105*2175Sjp161948=cut
106