NAME    [Toc]    [Back]

       DSA_set_default_method, DSA_get_default_method,
       DSA_set_method, DSA_new_method, DSA_OpenSSL - select DSA
       method

LIBRARY    [Toc]    [Back]

       libcrypto, -lcrypto

SYNOPSIS    [Toc]    [Back]

        #include <openssl/dsa.h>

        void DSA_set_default_method(DSA_METHOD *meth);

        DSA_METHOD *DSA_get_default_method(void);

        DSA_METHOD *DSA_set_method(DSA *dsa, DSA_METHOD *meth);

        DSA *DSA_new_method(DSA_METHOD *meth);

        DSA_METHOD *DSA_OpenSSL(void);

DESCRIPTION    [Toc]    [Back]

       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.

       Initially, the default is to use the OpenSSL internal
       implementation.  DSA_OpenSSL() returns a pointer to that
       method.

       DSA_set_default_method() makes meth the default method for
       all DSA structures created later.

       DSA_get_default_method() returns a pointer to the current
       default method.

       DSA_set_method() selects meth for all operations using the
       structure dsa.

       DSA_new_method() allocates and initializes a DSA structure
       so that method will be used for the DSA operations. If
       method is NULL, the default method is used.

THE DSA_METHOD STRUCTURE    [Toc]    [Back]

       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    [Toc]    [Back]

       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 a pointer to the DSA_METHOD previously
 associated with dsa.

       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    [Toc]    [Back]

       openssl_dsa(3), DSA_new(3)

HISTORY    [Toc]    [Back]

       DSA_set_default_method(), DSA_get_default_method(),
       DSA_set_method(), DSA_new_method() and DSA_OpenSSL() were
       added in OpenSSL 0.9.4.



2001-04-12                    0.9.6g            DSA_set_method(3)