Initial Commit

openssl-1.0.2f/doc/crypto/DSA_set_method.pod

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+=pod
+
+=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>
+ #include <openssl/engine.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);
+
+=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. IMPORTANT: See the NOTES section for
+important information about how these DSA API functions are affected by the use
+of B<ENGINE> API calls.
+
+Initially, the default DSA_METHOD is the OpenSSL internal implementation,
+as returned by DSA_OpenSSL().
+
+DSA_set_default_method() makes B<meth> the default method for all DSA
+structures created later. B<NB>: This is true only whilst no ENGINE has
+been set as a default for DSA, so this function is no longer recommended.
+
+DSA_get_default_method() returns a pointer to the current default
+DSA_METHOD. However, the meaningfulness of this result is dependent on
+whether the ENGINE API is being used, so this function is no longer 
+recommended.
+
+DSA_set_method() selects B<meth> to perform all operations using the key
+B<rsa>. This will replace the DSA_METHOD used by the DSA key and if the
+previous method was supplied by an ENGINE, the handle to that ENGINE will
+be released during the change. It is possible to have DSA keys that only
+work with certain DSA_METHOD implementations (eg. from an ENGINE module
+that supports embedded hardware-protected keys), 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 so that B<engine>
+will be used for the DSA operations. If B<engine> is NULL, the default engine
+for DSA operations is used, and if no default ENGINE is set, the DSA_METHOD
+controlled by DSA_set_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 non-zero if the provided B<meth> was successfully set as
+the method for B<dsa> (including unloading the ENGINE handle if the previous
+method was supplied by an 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 NOTES
+
+As of version 0.9.7, DSA_METHOD implementations are grouped together with other
+algorithmic APIs (eg. RSA_METHOD, EVP_CIPHER, etc) in B<ENGINE> modules. If a
+default ENGINE is specified for DSA functionality using an ENGINE API function,
+that will override any DSA defaults set using the DSA API (ie.
+DSA_set_default_method()). For this reason, the ENGINE API is the recommended way
+to control default implementations for use in DSA and other cryptographic
+algorithms.
+
+=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 the engine version of OpenSSL 0.9.6. For
+0.9.7, the handling of defaults in the ENGINE API was restructured so that this
+change was reversed, and behaviour of the other functions resembled more closely
+the previous behaviour. The behaviour of defaults in the ENGINE API now
+transparently overrides the behaviour of defaults in the DSA API without
+requiring changing these function prototypes.
+
+=cut