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 
        #include 

        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 dur-
       ing 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 con-
       trolled 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 unload-
       ing 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 allo-
       cated 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 con-
       trol 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.

0.9.7c                      2002-10-29          DSA_set_method(3)

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