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