| =pod |
| |
| =head1 NAME |
| |
| DH_generate_parameters, DH_check - generate and check Diffie-Hellman parameters |
| |
| =head1 SYNOPSIS |
| |
| #include <openssl/dh.h> |
| |
| DH *DH_generate_parameters(int prime_len, int generator, |
| void (*callback)(int, int, void *), void *cb_arg); |
| |
| int DH_check(DH *dh, int *codes); |
| |
| =head1 DESCRIPTION |
| |
| DH_generate_parameters() generates Diffie-Hellman parameters that can |
| be shared among a group of users, and returns them in a newly |
| allocated B<DH> structure. The pseudo-random number generator must be |
| seeded prior to calling DH_generate_parameters(). |
| |
| B<prime_len> is the length in bits of the safe prime to be generated. |
| B<generator> is a small number E<gt> 1, typically 2 or 5. |
| |
| A callback function may be used to provide feedback about the progress |
| of the key generation. If B<callback> is not B<NULL>, it will be |
| called as described in L<BN_generate_prime(3)|BN_generate_prime(3)> while a random prime |
| number is generated, and when a prime has been found, B<callback(3, |
| 0, cb_arg)> is called. |
| |
| DH_check() validates Diffie-Hellman parameters. It checks that B<p> is |
| a safe prime, and that B<g> is a suitable generator. In the case of an |
| error, the bit flags DH_CHECK_P_NOT_SAFE_PRIME or |
| DH_NOT_SUITABLE_GENERATOR are set in B<*codes>. |
| DH_UNABLE_TO_CHECK_GENERATOR is set if the generator cannot be |
| checked, i.e. it does not equal 2 or 5. |
| |
| =head1 RETURN VALUES |
| |
| DH_generate_parameters() returns a pointer to the DH structure, or |
| NULL if the parameter generation fails. The error codes can be |
| obtained by L<ERR_get_error(3)|ERR_get_error(3)>. |
| |
| DH_check() returns 1 if the check could be performed, 0 otherwise. |
| |
| =head1 NOTES |
| |
| DH_generate_parameters() may run for several hours before finding a |
| suitable prime. |
| |
| The parameters generated by DH_generate_parameters() are not to be |
| used in signature schemes. |
| |
| =head1 BUGS |
| |
| If B<generator> is not 2 or 5, B<dh-E<gt>g>=B<generator> is not |
| a usable generator. |
| |
| =head1 SEE ALSO |
| |
| L<dh(3)|dh(3)>, L<ERR_get_error(3)|ERR_get_error(3)>, L<rand(3)|rand(3)>, |
| L<DH_free(3)|DH_free(3)> |
| |
| =head1 HISTORY |
| |
| DH_check() is available in all versions of SSLeay and OpenSSL. |
| The B<cb_arg> argument to DH_generate_parameters() was added in SSLeay 0.9.0. |
| |
| In versions before OpenSSL 0.9.5, DH_CHECK_P_NOT_STRONG_PRIME is used |
| instead of DH_CHECK_P_NOT_SAFE_PRIME. |
| |
| =cut |
