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DH_SET_METHOD(3)
Contents
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DH_set_default_method, DH_get_default_method,
DH_set_method, DH_new_method, DH_OpenSSL - select DH
method
#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);
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 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 [Toc] [Back] 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;
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.
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.
dh(3), DH_new(3)
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.
OpenBSD 3.6 2002-09-14 3 [ Back ] |