DSA_OpenSSL (3)

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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>
 #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);

DESCRIPTION

A specifies the functions that OpenSSL uses for operations. By modifying the method, alternative implementations such as hardware accelerators may be used. See the section for important information about how these functions are affected by the use of calls.

Initially, the default

is the OpenSSL internal implementation, as returned by DSA_OpenSSL().

DSA_set_default_method() makes meth the default method for all

structures created later. : This is true only whilst no has been set as a default for so this function is no longer recommended.

DSA_get_default_method() returns a pointer to the current default

However, the meaningfulness of this result is dependent on whether the is being used, so this function is no longer recommended.

DSA_set_method() selects meth to perform all operations using the key rsa. This will replace the

used by the key and if the previous method was supplied by an the handle to that will be released during the change. It is possible to have keys that only work with certain implementations (eg. from an module that supports embedded hardware-protected keys), and in such cases attempting to change the for the key can have unexpected results.

DSA_new_method() allocates and initializes a

structure so that engine will be used for the operations. If engine is the default engine for operations is used, and if no default is set, the controlled by DSA_set_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);

     /* 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 s.

DSA_set_default_method() returns no value.

DSA_set_method() returns non-zero if the provided meth was successfully set as the method for dsa (including unloading the

handle if the previous method was supplied by an ).

DSA_new_method() returns

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.

NOTES

As of version 0.9.7, implementations are grouped together with other algorithmic APIs (eg. etc) in modules. If a default is specified for functionality using an function, that will override any defaults set using the (ie. DSA_set_default_method()). For this reason, the is the recommended way to control default implementations for use in and other cryptographic algorithms.

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.

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

s rather than s during development of the engine version of OpenSSL 0.9.6. For 0.9.7, the handling of defaults in the 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 now transparently overrides the behaviour of defaults in the without requiring changing these function prototypes.