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DH_generate_parameters(3)                          OpenSSL                         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.

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.



50                                               2013-03-05                        DH_generate_parameters(3)