1=pod
2
3=head1 NAME
4
5DSA_generate_parameters_ex, DSA_generate_parameters - generate DSA parameters
6
7=head1 SYNOPSIS
8
9 #include <openssl/dsa.h>
10
11 int DSA_generate_parameters_ex(DSA *dsa, int bits,
12		const unsigned char *seed,int seed_len,
13		int *counter_ret, unsigned long *h_ret, BN_GENCB *cb);
14
15Deprecated:
16
17 DSA *DSA_generate_parameters(int bits, unsigned char *seed,
18                int seed_len, int *counter_ret, unsigned long *h_ret,
19		void (*callback)(int, int, void *), void *cb_arg);
20
21=head1 DESCRIPTION
22
23DSA_generate_parameters_ex() generates primes p and q and a generator g
24for use in the DSA and stores the result in B<dsa>.
25
26B<bits> is the length of the prime to be generated; the DSS allows a
27maximum of 1024 bits.
28
29If B<seed> is B<NULL> or B<seed_len> E<lt> 20, the primes will be
30generated at random. Otherwise, the seed is used to generate
31them. If the given seed does not yield a prime q, a new random
32seed is chosen.
33
34DSA_generate_parameters_ex() places the iteration count in
35*B<counter_ret> and a counter used for finding a generator in
36*B<h_ret>, unless these are B<NULL>.
37
38A callback function may be used to provide feedback about the progress
39of the key generation. If B<cb> is not B<NULL>, it will be
40called as shown below. For information on the BN_GENCB structure and the
41BN_GENCB_call function discussed below, refer to
42L<BN_generate_prime(3)|BN_generate_prime(3)>.
43
44=over 4
45
46=item *
47
48When a candidate for q is generated, B<BN_GENCB_call(cb, 0, m++)> is called
49(m is 0 for the first candidate).
50
51=item *
52
53When a candidate for q has passed a test by trial division,
54B<BN_GENCB_call(cb, 1, -1)> is called.
55While a candidate for q is tested by Miller-Rabin primality tests,
56B<BN_GENCB_call(cb, 1, i)> is called in the outer loop
57(once for each witness that confirms that the candidate may be prime);
58i is the loop counter (starting at 0).
59
60=item *
61
62When a prime q has been found, B<BN_GENCB_call(cb, 2, 0)> and
63B<BN_GENCB_call(cb, 3, 0)> are called.
64
65=item *
66
67Before a candidate for p (other than the first) is generated and tested,
68B<BN_GENCB_call(cb, 0, counter)> is called.
69
70=item *
71
72When a candidate for p has passed the test by trial division,
73B<BN_GENCB_call(cb, 1, -1)> is called.
74While it is tested by the Miller-Rabin primality test,
75B<BN_GENCB_call(cb, 1, i)> is called in the outer loop
76(once for each witness that confirms that the candidate may be prime).
77i is the loop counter (starting at 0).
78
79=item *
80
81When p has been found, B<BN_GENCB_call(cb, 2, 1)> is called.
82
83=item *
84
85When the generator has been found, B<BN_GENCB_call(cb, 3, 1)> is called.
86
87=back
88
89DSA_generate_parameters() (deprecated) works in much the same way as for DSA_generate_parameters_ex, except that no B<dsa> parameter is passed and
90instead a newly allocated B<DSA> structure is returned. Additionally "old
91style" callbacks are used instead of the newer BN_GENCB based approach.
92Refer to L<BN_generate_prime(3)|BN_generate_prime(3)> for further information.
93
94=head1 RETURN VALUE
95
96DSA_generate_parameters_ex() returns a 1 on success, or 0 otherwise.
97
98DSA_generate_parameters() returns a pointer to the DSA structure, or
99B<NULL> if the parameter generation fails.
100
101The error codes can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>.
102
103=head1 BUGS
104
105Seed lengths E<gt> 20 are not supported.
106
107=head1 SEE ALSO
108
109L<dsa(3)|dsa(3)>, L<ERR_get_error(3)|ERR_get_error(3)>, L<rand(3)|rand(3)>,
110L<DSA_free(3)|DSA_free(3)>, L<BN_generate_prime(3)|BN_generate_prime(3)>
111
112=head1 HISTORY
113
114DSA_generate_parameters() appeared in SSLeay 0.8. The B<cb_arg>
115argument was added in SSLeay 0.9.0.
116In versions up to OpenSSL 0.9.4, B<callback(1, ...)> was called
117in the inner loop of the Miller-Rabin test whenever it reached the
118squaring step (the parameters to B<callback> did not reveal how many
119witnesses had been tested); since OpenSSL 0.9.5, B<callback(1, ...)>
120is called as in BN_is_prime(3), i.e. once for each witness.
121=cut
122