1=pod 2 3=head1 NAME 4 5DSA_set_default_method, DSA_get_default_method, 6DSA_set_method, DSA_new_method, DSA_OpenSSL - select DSA method 7 8=head1 SYNOPSIS 9 10 #include <openssl/dsa.h> 11 #include <openssl/engine.h> 12 13 void DSA_set_default_method(const DSA_METHOD *meth); 14 15 const DSA_METHOD *DSA_get_default_method(void); 16 17 int DSA_set_method(DSA *dsa, const DSA_METHOD *meth); 18 19 DSA *DSA_new_method(ENGINE *engine); 20 21 DSA_METHOD *DSA_OpenSSL(void); 22 23=head1 DESCRIPTION 24 25A B<DSA_METHOD> specifies the functions that OpenSSL uses for DSA 26operations. By modifying the method, alternative implementations 27such as hardware accelerators may be used. IMPORTANT: See the NOTES section for 28important information about how these DSA API functions are affected by the use 29of B<ENGINE> API calls. 30 31Initially, the default DSA_METHOD is the OpenSSL internal implementation, 32as returned by DSA_OpenSSL(). 33 34DSA_set_default_method() makes B<meth> the default method for all DSA 35structures created later. B<NB>: This is true only whilst no ENGINE has 36been set as a default for DSA, so this function is no longer recommended. 37 38DSA_get_default_method() returns a pointer to the current default 39DSA_METHOD. However, the meaningfulness of this result is dependent on 40whether the ENGINE API is being used, so this function is no longer 41recommended. 42 43DSA_set_method() selects B<meth> to perform all operations using the key 44B<rsa>. This will replace the DSA_METHOD used by the DSA key and if the 45previous method was supplied by an ENGINE, the handle to that ENGINE will 46be released during the change. It is possible to have DSA keys that only 47work with certain DSA_METHOD implementations (eg. from an ENGINE module 48that supports embedded hardware-protected keys), and in such cases 49attempting to change the DSA_METHOD for the key can have unexpected 50results. 51 52DSA_new_method() allocates and initializes a DSA structure so that B<engine> 53will be used for the DSA operations. If B<engine> is NULL, the default engine 54for DSA operations is used, and if no default ENGINE is set, the DSA_METHOD 55controlled by DSA_set_default_method() is used. 56 57=head1 THE DSA_METHOD STRUCTURE 58 59struct 60 { 61 /* name of the implementation */ 62 const char *name; 63 64 /* sign */ 65 DSA_SIG *(*dsa_do_sign)(const unsigned char *dgst, int dlen, 66 DSA *dsa); 67 68 /* pre-compute k^-1 and r */ 69 int (*dsa_sign_setup)(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, 70 BIGNUM **rp); 71 72 /* verify */ 73 int (*dsa_do_verify)(const unsigned char *dgst, int dgst_len, 74 DSA_SIG *sig, DSA *dsa); 75 76 /* compute rr = a1^p1 * a2^p2 mod m (May be NULL for some 77 implementations) */ 78 int (*dsa_mod_exp)(DSA *dsa, BIGNUM *rr, BIGNUM *a1, BIGNUM *p1, 79 BIGNUM *a2, BIGNUM *p2, BIGNUM *m, 80 BN_CTX *ctx, BN_MONT_CTX *in_mont); 81 82 /* compute r = a ^ p mod m (May be NULL for some implementations) */ 83 int (*bn_mod_exp)(DSA *dsa, BIGNUM *r, BIGNUM *a, 84 const BIGNUM *p, const BIGNUM *m, 85 BN_CTX *ctx, BN_MONT_CTX *m_ctx); 86 87 /* called at DSA_new */ 88 int (*init)(DSA *DSA); 89 90 /* called at DSA_free */ 91 int (*finish)(DSA *DSA); 92 93 int flags; 94 95 char *app_data; /* ?? */ 96 97 } DSA_METHOD; 98 99=head1 RETURN VALUES 100 101DSA_OpenSSL() and DSA_get_default_method() return pointers to the respective 102B<DSA_METHOD>s. 103 104DSA_set_default_method() returns no value. 105 106DSA_set_method() returns non-zero if the provided B<meth> was successfully set as 107the method for B<dsa> (including unloading the ENGINE handle if the previous 108method was supplied by an ENGINE). 109 110DSA_new_method() returns NULL and sets an error code that can be 111obtained by L<ERR_get_error(3)|ERR_get_error(3)> if the allocation 112fails. Otherwise it returns a pointer to the newly allocated structure. 113 114=head1 NOTES 115 116As of version 0.9.7, DSA_METHOD implementations are grouped together with other 117algorithmic APIs (eg. RSA_METHOD, EVP_CIPHER, etc) in B<ENGINE> modules. If a 118default ENGINE is specified for DSA functionality using an ENGINE API function, 119that will override any DSA defaults set using the DSA API (ie. 120DSA_set_default_method()). For this reason, the ENGINE API is the recommended way 121to control default implementations for use in DSA and other cryptographic 122algorithms. 123 124=head1 SEE ALSO 125 126L<dsa(3)|dsa(3)>, L<DSA_new(3)|DSA_new(3)> 127 128=head1 HISTORY 129 130DSA_set_default_method(), DSA_get_default_method(), DSA_set_method(), 131DSA_new_method() and DSA_OpenSSL() were added in OpenSSL 0.9.4. 132 133DSA_set_default_openssl_method() and DSA_get_default_openssl_method() replaced 134DSA_set_default_method() and DSA_get_default_method() respectively, and 135DSA_set_method() and DSA_new_method() were altered to use B<ENGINE>s rather than 136B<DSA_METHOD>s during development of the engine version of OpenSSL 0.9.6. For 1370.9.7, the handling of defaults in the ENGINE API was restructured so that this 138change was reversed, and behaviour of the other functions resembled more closely 139the previous behaviour. The behaviour of defaults in the ENGINE API now 140transparently overrides the behaviour of defaults in the DSA API without 141requiring changing these function prototypes. 142 143=cut 144