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DH_set_method(3)
NAME
  DH_set_method, DH_set_default_openssl_method,
  DH_get_default_openssl_method, DH_new_method, DH_OpenSSL - Select DH method

SYNOPSIS
  #include <openssl/dh.h>
  #include <openssl/engine.h>

  void DH_set_default_openssl_method(
	  DH_METHOD *meth );

  DH_METHOD *DH_get_default_openssl_method(
	  void );

  int DH_set_method(
	  DH *dh, ENGINE *engine );

  DH *DH_new_method(
	  ENGINE *engine );

  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.	 The
  DH_OpenSSL() function returns a pointer to that method.

  The DH_set_default_openssl_method() function makes meth the default method
  for all DH structures created later.	This is true only while the default
  engine for Diffie-Hellman operations remains as openssl. Engines provide an
  encapsulation for implementations of one or more algorithms, and all the DH
  functions mentioned here operate within the scope of the default openssl
  engine.

  The DH_get_default_openssl_method() function returns a pointer to the
  current default method for the openssl engine.

  The DH_set_method() function selects engine as the engine that will be
  responsible for all operations using the structure dh. If this function
  completes successfully, then the dh structure will have its own functional
  reference of engine, so the caller should remember to free their own
  reference to engine when finished with it.  An engine's DH_METHOD can be
  retrieved (or set) by the ENGINE_get_DH() or ENGINE_set_DH() functions.

  The DH_new_method() function allocates and initializes a DH structure so
  that engine will be used for the DH operations.  If engine is NULL, the
  default engine for Diffie-Hellman operations is used.

  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);

	    /* 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
  The DH_OpenSSL() and DH_get_default_method() functions return pointers to
  the respective DH_METHODs.

  The DH_set_default_openssl_method() function returns no value.

  The DH_set_method() function returns non-zero if the engin associated with
  dh was successfully changed to engine.

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

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

  The DH_set_default_openssl_method() and DH_get_default_openssl_method()
  replaced DH_set_default_method() and DH_get_default_method() respectively,
  and DH_set_method() and DH_new_method() were altered to use ENGINEs rather
  than DH_METHODs during development of OpenSSL 0.9.6.

SEE ALSO
  Functions: dh(3), DH_new(3)

Index for Section 3

Alphabetical listing for D

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