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 dependant 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