DH_set_method(3) OpenSSL 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 dependent 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 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 VALUESDH_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 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 ALSOdh(3), DH_new(3)HISTORYDH_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.
0.9.8q 2007-11-19 DH_set_method(3)
