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 inter-
       nal 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 cur-
       rent 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 struc-
       ture 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 point-
       ers 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 alloca-
       tion 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 implemen-
       tations for use in DSA and other cryptographic algo-
       rithms.

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 dur-
       ing 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)
