DSA_set_method(3) OpenSSL DSA_set_method(3) NNAAMMEE DSA_set_default_method, DSA_get_default_method, DSA_set_method, DSA_new_method, DSA_OpenSSL - select DSA method SSYYNNOOPPSSIISS #include #include 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); DDEESSCCRRIIPPTTIIOONN A DDSSAA__MMEETTHHOODD specifies the functions that OpenSSL uses for DSA opera- tions. 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 EENNGGIINNEE API calls. Initially, the default DSA_METHOD is the OpenSSL internal implementa- tion, as returned by _D_S_A___O_p_e_n_S_S_L_(_). _D_S_A___s_e_t___d_e_f_a_u_l_t___m_e_t_h_o_d_(_) makes mmeetthh the default method for all DSA structures created later. NNBB: This is true only whilst no ENGINE has been set as a default for DSA, so this function is no longer recom- mended. _D_S_A___g_e_t___d_e_f_a_u_l_t___m_e_t_h_o_d_(_) 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. _D_S_A___s_e_t___m_e_t_h_o_d_(_) selects mmeetthh to perform all operations using the key rrssaa. 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. _D_S_A___n_e_w___m_e_t_h_o_d_(_) allocates and initializes a DSA structure so that eennggiinnee will be used for the DSA operations. If eennggiinnee is NULL, the default engine for DSA operations is used, and if no default ENGINE is set, the DSA_METHOD controlled by _D_S_A___s_e_t___d_e_f_a_u_l_t___m_e_t_h_o_d_(_) is used. TTHHEE DDSSAA__MMEETTHHOODD SSTTRRUUCCTTUURREE 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; RREETTUURRNN VVAALLUUEESS _D_S_A___O_p_e_n_S_S_L_(_) and _D_S_A___g_e_t___d_e_f_a_u_l_t___m_e_t_h_o_d_(_) return pointers to the respective DDSSAA__MMEETTHHOODDs. _D_S_A___s_e_t___d_e_f_a_u_l_t___m_e_t_h_o_d_(_) returns no value. _D_S_A___s_e_t___m_e_t_h_o_d_(_) returns non-zero if the provided mmeetthh was successfully set as the method for ddssaa (including unloading the ENGINE handle if the previous method was supplied by an ENGINE). _D_S_A___n_e_w___m_e_t_h_o_d_(_) returns NULL and sets an error code that can be obtained by _E_R_R___g_e_t___e_r_r_o_r(3) if the allocation fails. Otherwise it returns a pointer to the newly allocated structure. NNOOTTEESS As of version 0.9.7, DSA_METHOD implementations are grouped together with other algorithmic APIs (eg. RSA_METHOD, EVP_CIPHER, etc) in EENNGGIINNEE 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. _D_S_A___s_e_t___d_e_f_a_u_l_t___m_e_t_h_o_d_(_)). For this reason, the ENGINE API is the recommended way to control default implementations for use in DSA and other cryptographic algorithms. SSEEEE AALLSSOO _d_s_a(3), _D_S_A___n_e_w(3) HHIISSTTOORRYY _D_S_A___s_e_t___d_e_f_a_u_l_t___m_e_t_h_o_d_(_), _D_S_A___g_e_t___d_e_f_a_u_l_t___m_e_t_h_o_d_(_), _D_S_A___s_e_t___m_e_t_h_o_d_(_), _D_S_A___n_e_w___m_e_t_h_o_d_(_) and _D_S_A___O_p_e_n_S_S_L_(_) were added in OpenSSL 0.9.4. _D_S_A___s_e_t___d_e_f_a_u_l_t___o_p_e_n_s_s_l___m_e_t_h_o_d_(_) and _D_S_A___g_e_t___d_e_f_a_u_l_t___o_p_e_n_s_s_l___m_e_t_h_o_d_(_) replaced _D_S_A___s_e_t___d_e_f_a_u_l_t___m_e_t_h_o_d_(_) and _D_S_A___g_e_t___d_e_f_a_u_l_t___m_e_t_h_o_d_(_) respec- tively, and _D_S_A___s_e_t___m_e_t_h_o_d_(_) and _D_S_A___n_e_w___m_e_t_h_o_d_(_) were altered to use EENNGGIINNEEs rather than DDSSAA__MMEETTHHOODDs during development of the engine ver- sion 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 be- haviour of the other functions resembled more closely the previous be- haviour. 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. 1.0.2u 2019-12-20 DSA_set_method(3)