/xlv3/openssl/0.9.7e-sgipl1/work/0.9.7e-sgipl1/openssl-
0.9.7e/doc/crypto
Page 1 (printed 10/20/05)
DH_generate_parameters(25/Sep/2002 (0.9.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
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.
Page 1 (printed 10/20/05)
DH_generate_parameters(25/Sep/2002 (0.9.DH_generate_parameters(3)
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.
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