1=pod
2
3=head1 NAME
4
5DH_generate_parameters, DH_check - generate and check Diffie-Hellman parameters
6
7=head1 SYNOPSIS
8
9 #include <openssl/dh.h>
10
11 DH *DH_generate_parameters(int prime_len, int generator,
12     void (*callback)(int, int, void *), void *cb_arg);
13
14 int DH_check(DH *dh, int *codes);
15
16=head1 DESCRIPTION
17
18DH_generate_parameters() generates Diffie-Hellman parameters that can
19be shared among a group of users, and returns them in a newly
20allocated B<DH> structure. The pseudo-random number generator must be
21seeded prior to calling DH_generate_parameters().
22
23B<prime_len> is the length in bits of the safe prime to be generated.
24B<generator> is a small number E<gt> 1, typically 2 or 5.
25
26A callback function may be used to provide feedback about the progress
27of the key generation. If B<callback> is not B<NULL>, it will be
28called as described in L<BN_generate_prime(3)|BN_generate_prime(3)> while a random prime
29number is generated, and when a prime has been found, B<callback(3,
300, cb_arg)> is called.
31
32DH_check() validates Diffie-Hellman parameters. It checks that B<p> is
33a safe prime, and that B<g> is a suitable generator. In the case of an
34error, the bit flags DH_CHECK_P_NOT_SAFE_PRIME or
35DH_NOT_SUITABLE_GENERATOR are set in B<*codes>.
36DH_UNABLE_TO_CHECK_GENERATOR is set if the generator cannot be
37checked, i.e. it does not equal 2 or 5.
38
39=head1 RETURN VALUES
40
41DH_generate_parameters() returns a pointer to the DH structure, or
42NULL if the parameter generation fails. The error codes can be
43obtained by L<ERR_get_error(3)|ERR_get_error(3)>.
44
45DH_check() returns 1 if the check could be performed, 0 otherwise.
46
47=head1 NOTES
48
49DH_generate_parameters() may run for several hours before finding a
50suitable prime.
51
52The parameters generated by DH_generate_parameters() are not to be
53used in signature schemes.
54
55=head1 BUGS
56
57If B<generator> is not 2 or 5, B<dh-E<gt>g>=B<generator> is not
58a usable generator.
59
60=head1 SEE ALSO
61
62L<dh(3)|dh(3)>, L<ERR_get_error(3)|ERR_get_error(3)>, L<rand(3)|rand(3)>,
63L<DH_free(3)|DH_free(3)>
64
65=head1 HISTORY
66
67DH_check() is available in all versions of SSLeay and OpenSSL.
68The B<cb_arg> argument to DH_generate_parameters() was added in SSLeay 0.9.0.
69
70In versions before OpenSSL 0.9.5, DH_CHECK_P_NOT_STRONG_PRIME is used
71instead of DH_CHECK_P_NOT_SAFE_PRIME.
72
73=cut
74