DH_set_method(3)

     DH_set_method(3)       0.9.6h (2000-05-29)       DH_set_method(3)

     NAME
          DH_set_default_method, DH_get_default_method, DH_set_method,
          DH_new_method, DH_OpenSSL - select DH method

     SYNOPSIS
           #include <openssl/dh.h>

           void DH_set_default_method(DH_METHOD *meth);

           DH_METHOD *DH_get_default_method(void);

           DH_METHOD *DH_set_method(DH *dh, DH_METHOD *meth);

           DH *DH_new_method(DH_METHOD *meth);

           DH_METHOD *DH_OpenSSL(void);

     DESCRIPTION
          A DH_METHOD specifies the functions that OpenSSL uses for
          Diffie-Hellman operations. By modifying the method,
          alternative implementations such as hardware accelerators
          may be used.

          Initially, the default is to use the OpenSSL internal
          implementation.  DH_OpenSSL() returns a pointer to that
          method.

          DH_set_default_method() makes meth the default method for
          all DH structures created later.

          DH_get_default_method() returns a pointer to the current
          default method.

          DH_set_method() selects meth for all operations using the
          structure dh.

          DH_new_method() allocates and initializes a DH structure so
          that method will be used for the DH operations. If method is
          NULL, the default method is used.

     THE DH_METHOD STRUCTURE
           typedef struct dh_meth_st
           {
               /* name of the implementation */
                  const char *name;

               /* generate private and public DH values for key agreement */
                  int (*generate_key)(DH *dh);

               /* compute shared secret */
                  int (*compute_key)(unsigned char *key, BIGNUM *pub_key, DH *dh);

     Page 1                                         (printed 1/19/103)

     DH_set_method(3)       0.9.6h (2000-05-29)       DH_set_method(3)

               /* compute r = a ^ p mod m (May be NULL for some implementations) */
                  int (*bn_mod_exp)(DH *dh, BIGNUM *r, BIGNUM *a, const BIGNUM *p,
                                          const BIGNUM *m, BN_CTX *ctx,
                                          BN_MONT_CTX *m_ctx);

               /* called at DH_new */
                  int (*init)(DH *dh);

               /* called at DH_free */
                  int (*finish)(DH *dh);

                  int flags;

                  char *app_data; /* ?? */

           } DH_METHOD;

     RETURN VALUES
          DH_OpenSSL() and DH_get_default_method() return pointers to
          the respective DH_METHODs.

          DH_set_default_method() returns no value.

          DH_set_method() returns a pointer to the DH_METHOD
          previously associated with dh.

          DH_new_method() returns NULL and sets an error code that can
          be obtained by ERR_get_error(3) if the allocation fails.
          Otherwise it returns a pointer to the newly allocated
          structure.

     SEE ALSO
          dh(3), DH_new(3)

     HISTORY
          DH_set_default_method(), DH_get_default_method(),
          DH_set_method(), DH_new_method() and DH_OpenSSL() were added
          in OpenSSL 0.9.4.

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