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(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);

DESCRIPTION
A 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 meth 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 for all operations using the structure dsa.

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

DSA_set_default_method() returns no value.

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

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(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.