=pod =head1 NAME DH_generate_parameters, DH_check - generate and check Diffie-Hellman parameters =head1 SYNOPSIS #include 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 structure. The pseudo-random number generator must be seeded prior to calling DH_generate_parameters(). B is the length in bits of the safe prime to be generated. B is a small number E 1, typically 2 or 5. A callback function may be used to provide feedback about the progress of the key generation. If B is not B, it will be called as described in L while a random prime number is generated, and when a prime has been found, B is called. DH_check() validates Diffie-Hellman parameters. It checks that B

is a safe prime, and that B 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. 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 is not 2 or 5, Bg>=B is not a usable generator. =head1 SEE ALSO L, L, L, L =head1 HISTORY DH_check() is available in all versions of SSLeay and OpenSSL. The B 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