DH_generate_parameters(3)

     DH_generate_parameters(0.9.6h (2002-09-2DH_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

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     DH_generate_parameters(0.9.6h (2002-09-2DH_generate_parameters(3)

          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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