DSA_SET_METHOD(3)          Library Functions Manual          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(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 object contains pointers to the functions used for DSA
     operations.  By default, the internal implementation returned by
     DSA_OpenSSL() is used.  By selecting another method, alternative
     implementations such as hardware accelerators may be used.

     DSA_set_default_method() selects meth as 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 to perform all operations using the key
     dsa.  This replaces the DSA_METHOD used by the DSA key.  It is possible
     to have DSA keys that only work with certain DSA_METHOD implementations,
     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.  The engine
     argument is ignored and the default 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_METHOD.

     DSA_set_method() returns 1 on success or 0 on failure.  Currently, it
     cannot fail.

     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_meth_new(3), DSA_new(3)

HISTORY
     DSA_set_default_method(), DSA_get_default_method(), DSA_set_method(),
     DSA_new_method(), and DSA_OpenSSL() first appeared in OpenSSL 0.9.5 and
     have been available since OpenBSD 2.7.

Linux 6.8.2-arch2-1            November 19, 2023           Linux 6.8.2-arch2-1