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=head1 NAME

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

=head1 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);

=head1 DESCRIPTION

A B<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 B<meth> the default method for all B<DSA>
structures created later.

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

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

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

=head1 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;

=head1 RETURN VALUES

DSA_OpenSSL() and DSA_get_default_method() return pointers to the
respective B<DSA_METHOD>s.

DSA_set_default_method() returns no value.

DSA_set_method() returns a pointer to the B<DSA_METHOD> previously
associated with B<dsa>.

DSA_new_method() returns B<NULL> and sets an error code that can be
obtained by L<ERR_get_error(3)|ERR_get_error(3)> if the allocation
fails. Otherwise it returns a pointer to the newly allocated
structure.

=head1 SEE ALSO

L<dsa(3)|dsa(3)>, L<DSA_new(3)|DSA_new(3)>

=head1 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.

=cut