/xlv3/openssl/0.9.7e-sgipl1/work/0.9.7e-sgipl1/openssl-
0.9.7e/doc/crypto
Page 1 (printed 10/20/05)
DSA_set_method(3) 28/Oct/2002 (0.9.7e) 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 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
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DSA_set_method(3) 28/Oct/2002 (0.9.7e) DSA_set_method(3)
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.
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DSA_set_method(3) 28/Oct/2002 (0.9.7e) DSA_set_method(3)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.
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