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DH_generate_parameters(3)           OpenSSL          DH_generate_parameters(3)


NAME

       DH_generate_parameters_ex, DH_generate_parameters, DH_check - 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. 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 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_generate_prime(3) for information on the BN_GENCB_call()
       function.

       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_ex() and DH_check() return 1 if the check could
       be performed, 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).


NOTES

       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.


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.

1.0.2h                            2016-05-03         DH_generate_parameters(3)

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