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 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 DSA API functions are affected by the use of ENGINE
API calls.
Initially, the default DSA_METHOD is the OpenSSL internal implementation, 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
recommended.
DSA_get_default_method() returns a pointer to the current default DSA_METHOD. However, the
meaningfulness of this result is dependant 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 hardwareprotected
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 VALUES
DSA_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 ALSO
dsa(3), DSA_new(3)
HISTORY
DSA_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() respectively, and DSA_set_method() and
DSA_new_method() were altered to use ENGINEs rather than DSA_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 DSA API without requiring changing these function prototypes.
0.9.7l 2002-10-28 DSA_set_method(3)
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