NAME
DH_generate_parameters_ex,
DH_check,
DH_generate_parameters —
generate and check Diffie-Hellman
parameters
SYNOPSIS
#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);
DESCRIPTION
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.
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(3) while a random prime number is
generated, and when a prime has been found,
BN_GENCB_call(cb,
3, 0) is called; see
BN_GENCB_call(3).
DH_check()
validates Diffie-Hellman parameters. If no problems are found,
*codes is set to zero. Otherwise, one or more of the
following bits are set:
DH_CHECK_P_NOT_PRIME- The parameter dh->p is not prime.
DH_CHECK_P_NOT_SAFE_PRIME- The parameter dh->p is not a safe prime.
DH_UNABLE_TO_CHECK_GENERATOR- The generator dh->g cannot be checked for suitability: it is neither 2 nor 5.
DH_NOT_SUITABLE_GENERATOR- The generator dh->g is not suitable.
RETURN VALUES
DH_generate_parameters_ex() and
DH_check() return 1 if the check could be performed,
or 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(3).
SEE ALSO
HISTORY
DH_check() and
DH_generate_parameters() first appeared in SSLeay
0.5.1 and have been available since OpenBSD 2.4.
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.
DH_generate_parameters_ex() first appeared
in OpenSSL 0.9.8 and has been available since OpenBSD
4.5.
CAVEATS
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.
BUGS
If generator is not 2 or 5, dh->g=generator is not a usable generator.