=pod

=head1 NAME

DSA_set_default_openssl_method, DSA_get_default_openssl_method,
DSA_set_method, DSA_new_method, DSA_OpenSSL - select DSA method

=head1 SYNOPSIS

 #include <openssl/dsa.h>
 #include <openssl/engine.h>

 void DSA_set_default_openssl_method(DSA_METHOD *meth);

 DSA_METHOD *DSA_get_default_openssl_method(void);

 int DSA_set_method(DSA *dsa, ENGINE *engine);

 DSA *DSA_new_method(ENGINE *engine);

 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_openssl_method() makes B<meth> the default method for
all DSA structures created later. B<NB:> This is true only whilst the
default engine for DSA operations remains as "openssl". ENGINEs
provide an encapsulation for implementations of one or more algorithms at a
time, and all the DSA functions mentioned here operate within the scope
of the default "openssl" engine.

DSA_get_default_openssl_method() returns a pointer to the current default
method for the "openssl" engine.

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

DSA_new_method() allocates and initializes a DSA structure so that
B<engine> will be used for the DSA operations. If B<engine> is NULL,
the default engine for DSA operations 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_openssl_method() return pointers to the
respective DSA_METHODs.

DSA_set_default_openssl_method() returns no value.

DSA_set_method() returns non-zero if the ENGINE associated with B<dsa>
was successfully changed to B<engine>.

DSA_new_method() returns 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.

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 B<ENGINE>s
rather than B<DSA_METHOD>s during development of OpenSSL 0.9.6.

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