DH_generate_parameters_ex, DH_generate_parameters, DH_check - generate and check Diffie-Hellman parameters
#include <openssl/dh.h>
int DH_generate_parameters_ex(DH *dh, int prime_len,int generator, BN_GENCB *cb);
int DH_check(DH *dh, int *codes);
Deprecated:
DH *DH_generate_parameters(int prime_len, int generator,
void (*callback)(int, int, void *), void *cb_arg);
DH_generate_parameters_ex() generates Diffie-Hellman parameters that can
be shared among a group of users, and stores them in the provided DH
structure. The pseudo-random number generator must be
seeded prior to calling DH_generate_parameters().
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 cb is not NULL, it will be
called as described in BN_generate_prime while a random prime
number is generated, and when a prime has been found, BN_GENCB_call(cb, 3, 0)
is called. See BN_generate_prime for information on
the BN_GENCB_call() function.
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_generate_parameters_ex() and DH_check() return 1 if the check could be
performed, 0 otherwise.
DH_generate_parameters() (deprecated) returns a pointer to the DH structure, or
NULL if the parameter generation fails.
The error codes can be obtained by ERR_get_error.
DH_generate_parameters_ex() and DH_generate_parameters() may run for several
hours before finding a suitable prime.
The parameters generated by DH_generate_parameters_ex() and DH_generate_parameters()
are not to be used in signature schemes.
If generator is not 2 or 5, dh->g=generator is not a usable generator.
dh, ERR_get_error, rand, DH_free
DH_check() is available in all versions of SSLeay and OpenSSL.
The 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.