DH_generate_parameters(3)DH_generate_parameters(3)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
The DH_generate_parameters() function generates Diffie-Hellman parame‐
ters 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().
The prime_len is the length in bits of the safe prime to be generated.
The 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() while a random prime number is gener‐
ated, 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_GEN‐
ERATOR are set in *codes. DH_UNABLE_TO_CHECK_GENERATOR is set if the
generator cannot be checked, meaning it does not equal 2 or 5.
NOTES
The DH_generate_parameters() function 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.
RESTRICTIONS
If generator is not 2 or 5, dh->g=generator is not a usable generator.
RETURN VALUES
The DH_generate_parameters() function returns a pointer to the DH
structure, or NULL if the parameter generation fails. The error codes
can be obtained from ERR_get_error().
The DH_check() function returns 1 if the check could be performed, 0
otherwise.
HISTORY
The DH_check() function 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.
SEE ALSO
Functions: dh(3), err(3), rand(3), DH_free(3)DH_generate_parameters(3)
