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1=pod
2
3=head1 NAME
4
5DSA_set_default_method, DSA_get_default_method,
6DSA_set_method, DSA_new_method, DSA_OpenSSL,
7DSA_set_default_openssl_method, DSA_get_default_openssl_method
8- select DSA method
9
10=head1 SYNOPSIS
11
12 #include <openssl/dsa.h>
13 #include <openssl/engine.h>
14
15 void DSA_set_default_method(const DSA_METHOD *meth);
16
17 const DSA_METHOD *DSA_get_default_method(void);
18
19 int DSA_set_method(DSA *dsa, const DSA_METHOD *meth);
20
21 DSA *DSA_new_method(ENGINE *engine);
22
23 DSA_METHOD *DSA_OpenSSL(void);
24
25=head1 DESCRIPTION
26
27A B<DSA_METHOD> specifies the functions that OpenSSL uses for DSA
28operations. By modifying the method, alternative implementations
29such as hardware accelerators may be used. IMPORTANT: See the NOTES section for
30important information about how these DSA API functions are affected by the use
31of B<ENGINE> API calls.
32
33Initially, the default DSA_METHOD is the OpenSSL internal implementation,
34as returned by DSA_OpenSSL().
35
36DSA_set_default_method() makes B<meth> the default method for all DSA
37structures created later. B<NB>: This is true only whilst no ENGINE has
38been set as a default for DSA, so this function is no longer recommended.
39
40DSA_get_default_method() returns a pointer to the current default
41DSA_METHOD. However, the meaningfulness of this result is dependent on
42whether the ENGINE API is being used, so this function is no longer
43recommended.
44
45DSA_set_method() selects B<meth> to perform all operations using the key
46B<rsa>. This will replace the DSA_METHOD used by the DSA key and if the
47previous method was supplied by an ENGINE, the handle to that ENGINE will
48be released during the change. It is possible to have DSA keys that only
49work with certain DSA_METHOD implementations (eg. from an ENGINE module
50that supports embedded hardware-protected keys), and in such cases
51attempting to change the DSA_METHOD for the key can have unexpected
52results.
53
54DSA_new_method() allocates and initializes a DSA structure so that B<engine>
55will be used for the DSA operations. If B<engine> is NULL, the default engine
56for DSA operations is used, and if no default ENGINE is set, the DSA_METHOD
57controlled by DSA_set_default_method() is used.
58
59=head1 THE DSA_METHOD STRUCTURE
60
61struct
62 {
63 /* name of the implementation */
64 const char *name;
65
66 /* sign */
67 DSA_SIG *(*dsa_do_sign)(const unsigned char *dgst, int dlen,
68 DSA *dsa);
69
70 /* pre-compute k^-1 and r */
71 int (*dsa_sign_setup)(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
72 BIGNUM **rp);
73
74 /* verify */
75 int (*dsa_do_verify)(const unsigned char *dgst, int dgst_len,
76 DSA_SIG *sig, DSA *dsa);
77
78 /* compute rr = a1^p1 * a2^p2 mod m (May be NULL for some
79 implementations) */
80 int (*dsa_mod_exp)(DSA *dsa, BIGNUM *rr, BIGNUM *a1, BIGNUM *p1,
81 BIGNUM *a2, BIGNUM *p2, BIGNUM *m,
82 BN_CTX *ctx, BN_MONT_CTX *in_mont);
83
84 /* compute r = a ^ p mod m (May be NULL for some implementations) */
85 int (*bn_mod_exp)(DSA *dsa, BIGNUM *r, BIGNUM *a,
86 const BIGNUM *p, const BIGNUM *m,
87 BN_CTX *ctx, BN_MONT_CTX *m_ctx);
88
89 /* called at DSA_new */
90 int (*init)(DSA *DSA);
91
92 /* called at DSA_free */
93 int (*finish)(DSA *DSA);
94
95 int flags;
96
97 char *app_data; /* ?? */
98
99 } DSA_METHOD;
100
101=head1 RETURN VALUES
102
103DSA_OpenSSL() and DSA_get_default_method() return pointers to the respective
104B<DSA_METHOD>s.
105
106DSA_set_default_method() returns no value.
107
108DSA_set_method() returns non-zero if the provided B<meth> was successfully set
109as the method for B<dsa> (including unloading the ENGINE handle if the previous
110method was supplied by an ENGINE).
111
112DSA_new_method() returns NULL and sets an error code that can be
113obtained by L<ERR_get_error(3)|ERR_get_error(3)> if the allocation
114fails. Otherwise it returns a pointer to the newly allocated structure.
115
116=head1 NOTES
117
118As of version 0.9.7, DSA_METHOD implementations are grouped together with other
119algorithmic APIs (eg. RSA_METHOD, EVP_CIPHER, etc) in B<ENGINE> modules. If a
120default ENGINE is specified for DSA functionality using an ENGINE API function,
121that will override any DSA defaults set using the DSA API (ie.
122DSA_set_default_method()). For this reason, the ENGINE API is the recommended
123way to control default implementations for use in DSA and other cryptographic
124algorithms.
125
126=head1 SEE ALSO
127
128L<dsa(3)|dsa(3)>, L<DSA_new(3)|DSA_new(3)>
129
130=head1 HISTORY
131
132DSA_set_default_method(), DSA_get_default_method(), DSA_set_method(),
133DSA_new_method() and DSA_OpenSSL() were added in OpenSSL 0.9.4.
134
135DSA_set_default_openssl_method() and DSA_get_default_openssl_method() replaced
136DSA_set_default_method() and DSA_get_default_method() respectively, and
137DSA_set_method() and DSA_new_method() were altered to use B<ENGINE>s rather than
138B<DSA_METHOD>s during development of the engine version of OpenSSL 0.9.6. For
1390.9.7, the handling of defaults in the ENGINE API was restructured so that this
140change was reversed, and behaviour of the other functions resembled more closely
141the previous behaviour. The behaviour of defaults in the ENGINE API now
142transparently overrides the behaviour of defaults in the DSA API without
143requiring changing these function prototypes.
144
145=cut