DH_OpenSSL man page on IRIX

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     /xlv3/openssl/0.9.7e-sgipl1/work/0.9.7e-sgipl1/openssl-
     0.9.7e/doc/crypto

     Page 1					    (printed 10/20/05)

     DH_set_method(3)	   28/Oct/2002 (0.9.7e)	      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>
	   #include <openssl/engine.h>

	   void DH_set_default_method(const DH_METHOD *meth);

	   const DH_METHOD *DH_get_default_method(void);

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

	   DH *DH_new_method(ENGINE *engine);

	   const 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. IMPORTANT: See the NOTES section for important
	  information about how these DH API functions are affected by
	  the use of ENGINE API calls.

	  Initially, the default DH_METHOD is the OpenSSL internal
	  implementation, as returned by DH_OpenSSL().

	  DH_set_default_method() makes meth the default method for
	  all DH structures created later. NB: This is true only
	  whilst no ENGINE has been set as a default for DH, so this
	  function is no longer recommended.

	  DH_get_default_method() returns a pointer to the current
	  default DH_METHOD.  However, the meaningfulness of this
	  result is dependant on whether the ENGINE API is being used,
	  so this function is no longer recommended.

	  DH_set_method() selects meth to perform all operations using
	  the key dh.  This will replace the DH_METHOD used by the DH
	  key and if the previous method was supplied by an ENGINE,
	  the handle to that ENGINE will be released during the
	  change. It is possible to have DH keys that only work with
	  certain DH_METHOD implementations (eg. from an ENGINE module
	  that supports embedded hardware-protected keys), and in such
	  cases attempting to change the DH_METHOD for the key can
	  have unexpected results.

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

     Page 1					    (printed 10/20/05)

     DH_set_method(3)	   28/Oct/2002 (0.9.7e)	      DH_set_method(3)

	  NULL, the default ENGINE for DH operations is used, and if
	  no default ENGINE is set, the DH_METHOD controlled by
	  DH_set_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);

	       /* 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 non-zero if the provided meth was
	  successfully set as the method for dh (including unloading
	  the ENGINE handle if the previous method was supplied by an
	  ENGINE).

	  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.

     NOTES
	  As of version 0.9.7, DH_METHOD implementations are grouped

     Page 2					    (printed 10/20/05)

     DH_set_method(3)	   28/Oct/2002 (0.9.7e)	      DH_set_method(3)

	  together with other algorithmic APIs (eg. RSA_METHOD,
	  EVP_CIPHER, etc) in ENGINE modules. If a default ENGINE is
	  specified for DH functionality using an ENGINE API function,
	  that will override any DH defaults set using the DH API (ie.
	  DH_set_default_method()). For this reason, the ENGINE API is
	  the recommended way to control default implementations for
	  use in DH and other cryptographic algorithms.

     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.

	  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 the engine version of OpenSSL 0.9.6. For
	  0.9.7, the handling of defaults in the ENGINE API was
	  restructured so that this change was reversed, and behaviour
	  of the other functions resembled more closely the previous
	  behaviour. The behaviour of defaults in the ENGINE API now
	  transparently overrides the behaviour of defaults in the DH
	  API without requiring changing these function prototypes.

     Page 3					    (printed 10/20/05)

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