NAME¶
DH_generate_parameters, DH_check - generate and check Diffie-Hellman parameters
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);
DESCRIPTION¶
DH_generate_parameters() generates Diffie-Hellman parameters that can be
shared among a group of users, and returns them in a newly allocated
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
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.
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
ERR_get_error(3).
DH_check() returns 1 if the check could be performed, 0 otherwise.
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.
BUGS¶
If
generator is not 2 or 5,
dh->g=
generator is not a
usable generator.
SEE ALSO¶
dh(3),
ERR_get_error(3),
rand(3),
DH_free(3)
HISTORY¶
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.