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1 | =pod | ||
2 | |||
3 | =head1 NAME | ||
4 | |||
5 | DSA_set_default_method, DSA_get_default_method, | ||
6 | DSA_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 | |||
25 | A B<DSA_METHOD> specifies the functions that OpenSSL uses for DSA | ||
26 | operations. By modifying the method, alternative implementations | ||
27 | such as hardware accelerators may be used. IMPORTANT: See the NOTES section for | ||
28 | important information about how these DSA API functions are affected by the use | ||
29 | of B<ENGINE> API calls. | ||
30 | |||
31 | Initially, the default DSA_METHOD is the OpenSSL internal implementation, | ||
32 | as returned by DSA_OpenSSL(). | ||
33 | |||
34 | DSA_set_default_method() makes B<meth> the default method for all DSA | ||
35 | structures created later. B<NB>: This is true only whilst no ENGINE has | ||
36 | been set as a default for DSA, so this function is no longer recommended. | ||
37 | |||
38 | DSA_get_default_method() returns a pointer to the current default | ||
39 | DSA_METHOD. However, the meaningfulness of this result is dependent on | ||
40 | whether the ENGINE API is being used, so this function is no longer | ||
41 | recommended. | ||
42 | |||
43 | DSA_set_method() selects B<meth> to perform all operations using the key | ||
44 | B<rsa>. This will replace the DSA_METHOD used by the DSA key and if the | ||
45 | previous method was supplied by an ENGINE, the handle to that ENGINE will | ||
46 | be released during the change. It is possible to have DSA keys that only | ||
47 | work with certain DSA_METHOD implementations (eg. from an ENGINE module | ||
48 | that supports embedded hardware-protected keys), and in such cases | ||
49 | attempting to change the DSA_METHOD for the key can have unexpected | ||
50 | results. | ||
51 | |||
52 | DSA_new_method() allocates and initializes a DSA structure so that B<engine> | ||
53 | will be used for the DSA operations. If B<engine> is NULL, the default engine | ||
54 | for DSA operations is used, and if no default ENGINE is set, the DSA_METHOD | ||
55 | controlled by DSA_set_default_method() is used. | ||
56 | |||
57 | =head1 THE DSA_METHOD STRUCTURE | ||
58 | |||
59 | struct | ||
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 | |||
101 | DSA_OpenSSL() and DSA_get_default_method() return pointers to the respective | ||
102 | B<DSA_METHOD>s. | ||
103 | |||
104 | DSA_set_default_method() returns no value. | ||
105 | |||
106 | DSA_set_method() returns non-zero if the provided B<meth> was successfully set as | ||
107 | the method for B<dsa> (including unloading the ENGINE handle if the previous | ||
108 | method was supplied by an ENGINE). | ||
109 | |||
110 | DSA_new_method() returns NULL and sets an error code that can be | ||
111 | obtained by L<ERR_get_error(3)|ERR_get_error(3)> if the allocation | ||
112 | fails. Otherwise it returns a pointer to the newly allocated structure. | ||
113 | |||
114 | =head1 NOTES | ||
115 | |||
116 | As of version 0.9.7, DSA_METHOD implementations are grouped together with other | ||
117 | algorithmic APIs (eg. RSA_METHOD, EVP_CIPHER, etc) in B<ENGINE> modules. If a | ||
118 | default ENGINE is specified for DSA functionality using an ENGINE API function, | ||
119 | that will override any DSA defaults set using the DSA API (ie. | ||
120 | DSA_set_default_method()). For this reason, the ENGINE API is the recommended way | ||
121 | to control default implementations for use in DSA and other cryptographic | ||
122 | algorithms. | ||
123 | |||
124 | =head1 SEE ALSO | ||
125 | |||
126 | L<dsa(3)|dsa(3)>, L<DSA_new(3)|DSA_new(3)> | ||
127 | |||
128 | =head1 HISTORY | ||
129 | |||
130 | DSA_set_default_method(), DSA_get_default_method(), DSA_set_method(), | ||
131 | DSA_new_method() and DSA_OpenSSL() were added in OpenSSL 0.9.4. | ||
132 | |||
133 | DSA_set_default_openssl_method() and DSA_get_default_openssl_method() replaced | ||
134 | DSA_set_default_method() and DSA_get_default_method() respectively, and | ||
135 | DSA_set_method() and DSA_new_method() were altered to use B<ENGINE>s rather than | ||
136 | B<DSA_METHOD>s during development of the engine version of OpenSSL 0.9.6. For | ||
137 | 0.9.7, the handling of defaults in the ENGINE API was restructured so that this | ||
138 | change was reversed, and behaviour of the other functions resembled more closely | ||
139 | the previous behaviour. The behaviour of defaults in the ENGINE API now | ||
140 | transparently overrides the behaviour of defaults in the DSA API without | ||
141 | requiring changing these function prototypes. | ||
142 | |||
143 | =cut | ||