/usr/man2/cat.3/DH_set_default_method.3.Z(/usr/man2/cat.3/DH_set_default_method.3.Z)
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-Hell-
man 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 implementa-
tion, as returned by DH_OpenSSL().
DH_set_default_method() makes meth the default method for all DH struc-
tures 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 pre-
vious 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 respec-
tive 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() respec-
tively, 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 be-
haviour of defaults in the ENGINE API now transparently overrides the
behaviour of defaults in the DH API without requiring changing these
function prototypes.
1.0.2t 2019-09-10 DH_set_method(3)
See also DH_OpenSSL(3)
See also DH_get_default_method(3)
See also DH_new_method(3)
See also DH_set_method(3)
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