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. See the CAVEATS section for how these DSA API functions are affected by the use of engine(3) 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.
Note: 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 dependent on whether the
engine(3) API is being used, so this function is no longer
recommended.
DSA_set_method
()
selects meth to perform all operations using the key
dsa. 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 (e.g. 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 is defined as follows:
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_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.
SEE ALSO
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.
CAVEATS
As of version 0.9.7, DSA_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 DSA functionality using an engine(3) API function, that will override any DSA defaults set using the DSA API (i.e. DSA_set_default_method). For this reason, the engine(3) API is the recommended way to control default implementations for use in DSA and other cryptographic algorithms.