DSA_set_method(3)

     DSA_set_method(3)      0.9.6h (2000-05-29)      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>

           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
          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
          struct
           {
               /* name of the implementation */
                  const char *name;

               /* sign */
                  DSA_SIG *(*dsa_do_sign)(const unsigned char *dgst, int dlen,
                                           DSA *dsa);

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     DSA_set_method(3)      0.9.6h (2000-05-29)      DSA_set_method(3)

               /* 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 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
          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.

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