DSA_set_method(3) OpenSSL DSA_set_method(3)NAME
DSA_set_default_method, DSA_get_default_method, DSA_set_method,
DSA_new_method, DSA_OpenSSL - select DSA method
SYNOPSIS
#include <openssl/dsa.h>
#include <openssl/engine.h>
void DSA_set_default_method(const DSA_METHOD *meth);
const DSA_METHOD *DSA_get_default_method(void);
int DSA_set_method(DSA *dsa, const DSA_METHOD *meth);
DSA *DSA_new_method(ENGINE *engine);
DSA_METHOD *DSA_OpenSSL(void);
DESCRIPTION
A DSA_METHOD specifies the functions that OpenSSL uses for DSA opera‐
tions. By modifying the method, alternative implementations such as
hardware accelerators may be used. IMPORTANT: See the NOTES section for
important information about how these DSA API functions are affected by
the use of ENGINE API calls.
Initially, the default DSA_METHOD is the OpenSSL internal implementa‐
tion, as returned by DSA_OpenSSL().
DSA_set_default_method() makes meth the default method for all DSA
structures created later. NB: This is true only whilst no ENGINE has
been set as a default for DSA, so this function is no longer recom‐
mended.
DSA_get_default_method() returns a pointer to the current default
DSA_METHOD. However, the meaningfulness of this result is dependent on
whether the ENGINE API is being used, so this function is no longer
recommended.
DSA_set_method() selects meth to perform all operations using the key
rsa. This will replace the DSA_METHOD used by the DSA 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 DSA keys
that only work with certain DSA_METHOD implementations (eg. from an
ENGINE module that supports embedded hardware-protected keys), and in
such cases attempting to change the DSA_METHOD for the key can have
unexpected results.
DSA_new_method() allocates and initializes a DSA structure so that
engine will be used for the DSA operations. If engine is NULL, the
default engine for DSA operations is used, and if no default ENGINE is
set, the DSA_METHOD controlled by DSA_set_default_method() is used.
THE DSA_METHOD STRUCTURE
struct
{
/* name of the implementation */
const char *name;
/* sign */
DSA_SIG *(*dsa_do_sign)(const unsigned char *dgst, int dlen,
DSA *dsa);
/* pre-compute k^-1 and r */
int (*dsa_sign_setup)(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
BIGNUM **rp);
/* verify */
int (*dsa_do_verify)(const unsigned char *dgst, int dgst_len,
DSA_SIG *sig, DSA *dsa);
/* compute rr = a1^p1 * a2^p2 mod m (May be NULL for some
implementations) */
int (*dsa_mod_exp)(DSA *dsa, BIGNUM *rr, BIGNUM *a1, BIGNUM *p1,
BIGNUM *a2, BIGNUM *p2, BIGNUM *m,
BN_CTX *ctx, BN_MONT_CTX *in_mont);
/* compute r = a ^ p mod m (May be NULL for some implementations) */
int (*bn_mod_exp)(DSA *dsa, BIGNUM *r, BIGNUM *a,
const BIGNUM *p, const BIGNUM *m,
BN_CTX *ctx, BN_MONT_CTX *m_ctx);
/* called at DSA_new */
int (*init)(DSA *DSA);
/* called at DSA_free */
int (*finish)(DSA *DSA);
int flags;
char *app_data; /* ?? */
} DSA_METHOD;
RETURN VALUESDSA_OpenSSL() and DSA_get_default_method() return pointers to the
respective DSA_METHODs.
DSA_set_default_method() returns no value.
DSA_set_method() returns non-zero if the provided meth was successfully
set as the method for dsa (including unloading the ENGINE handle if the
previous method was supplied by an ENGINE).
DSA_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, DSA_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 DSA functionality using
an ENGINE API function, that will override any DSA defaults set using
the DSA API (ie. DSA_set_default_method()). For this reason, the
ENGINE API is the recommended way to control default implementations
for use in DSA and other cryptographic algorithms.
SEE ALSOdsa(3), DSA_new(3)HISTORYDSA_set_default_method(), DSA_get_default_method(), DSA_set_method(),
DSA_new_method() and DSA_OpenSSL() were added in OpenSSL 0.9.4.
DSA_set_default_openssl_method() and DSA_get_default_openssl_method()
replaced DSA_set_default_method() and DSA_get_default_method() respec‐
tively, and DSA_set_method() and DSA_new_method() were altered to use
ENGINEs rather than DSA_METHODs during development of the engine ver‐
sion 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 be‐
haviour of the other functions resembled more closely the previous be‐
haviour. The behaviour of defaults in the ENGINE API now transparently
overrides the behaviour of defaults in the DSA API without requiring
changing these function prototypes.
1.0.0h 2007-11-19 DSA_set_method(3)
