NAME    [Toc]    [Back]

       DH_generate_parameters, DH_check - generate and check
       Diffie-Hellman parameters

LIBRARY    [Toc]    [Back]

       libcrypto, -lcrypto

SYNOPSIS    [Toc]    [Back]

        #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    [Toc]    [Back]

       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    [Toc]    [Back]

       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    [Toc]    [Back]

       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    [Toc]    [Back]

       If generator is not 2 or 5, dh->g=generator is not a
       usable generator.

SEE ALSO    [Toc]    [Back]

       openssl_dh(3), openssl_err(3), openssl_rand(3), DH_free(3)

HISTORY    [Toc]    [Back]

       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.



2000-07-22                    0.9.6g    DH_generate_parameters(3)