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>
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. See the CAVEATS section for how these DH API functions are affected by the use of engine(3) 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(3) 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 (e.g. 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 is defined as follows:
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_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.
SEE ALSO
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.
CAVEATS
As of version 0.9.7, DH_METHOD
implementations are grouped together with other algorithmic APIs (e.g.
RSA_METHOD, EVP_CIPHER) in ENGINE modules. If a
default ENGINE is specified for DH functionality using
an engine(3) API function, that will override any DH defaults set using
the DH API (i.e. DH_set_default_method
()). For this
reason, the engine(3) API is the recommended way to control default
implementations for use in DH and other cryptographic algorithms.