DSA_generate_parameters.pod revision 291721 
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.
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