DH *DH_generate_parameters(int prime_len, int generator, void (*callback)(int, int, void *), void *cb_arg);
int DH_check(DH *dh, int *codes);
prime_len is the length in bits of the safe prime to be generated. generator is a small number > 1, typically 2 or 5.
A callback function may be used to provide feedback about the progress of the key generation. If callback is not NULL, it will be called as described in BN_generate_prime(3) while a random prime number is generated, and when a prime has been found, callback(3, 0, cb_arg) is called.
DH_check() validates Diffie-Hellman parameters. It checks that p is a safe prime, and that 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 *codes. DH_UNABLE_TO_CHECK_GENERATOR is set if the generator cannot be checked, i.e. it does not equal 2 or 5.
DH_check() returns 1 if the check could be performed, 0 otherwise.
The parameters generated by DH_generate_parameters() are not to be used in signature schemes.
In versions before OpenSSL 0.9.5, DH_CHECK_P_NOT_STRONG_PRIME is used instead of DH_CHECK_P_NOT_SAFE_PRIME.