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 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 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.