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