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1.\" $OpenBSD: DSA_set_method.3,v 1.13 2025/06/08 22:40:29 schwarze Exp $
2.\" OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100
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51.Dd $Mdocdate: June 8 2025 $
52.Dt DSA_SET_METHOD 3
53.Os
54.Sh NAME
55.Nm DSA_set_default_method ,
56.Nm DSA_get_default_method ,
57.Nm DSA_set_method ,
58.Nm DSA_new_method ,
59.Nm DSA_OpenSSL
60.Nd select DSA method
61.Sh SYNOPSIS
62.Lb libcrypto
63.In openssl/dsa.h
64.Ft void
65.Fo DSA_set_default_method
66.Fa "const DSA_METHOD *meth"
67.Fc
68.Ft const DSA_METHOD *
69.Fn DSA_get_default_method void
70.Ft int
71.Fo DSA_set_method
72.Fa "DSA *dsa"
73.Fa "const DSA_METHOD *meth"
74.Fc
75.Ft DSA *
76.Fo DSA_new_method
77.Fa "ENGINE *engine"
78.Fc
79.Ft DSA_METHOD *
80.Fn DSA_OpenSSL void
81.Sh DESCRIPTION
82A
83.Vt DSA_METHOD
84object contains pointers to the functions used for DSA operations.
85By default, the internal implementation returned by
86.Fn DSA_OpenSSL
87is used.
88By selecting another method, alternative implementations
89such as hardware accelerators may be used.
90.Pp
91.Fn DSA_set_default_method
92selects
93.Fa meth
94as the default method for all
95.Vt DSA
96structures created later.
97.Pp
98.Fn DSA_get_default_method
99returns a pointer to the current default method.
100.Pp
101.Fn DSA_set_method
102selects
103.Fa meth
104to perform all operations using the key
105.Fa dsa .
106This replaces the
107.Vt DSA_METHOD
108used by the DSA key.
109It is possible to have DSA keys that only work with certain
110.Vt DSA_METHOD
111implementations,
112and in such cases attempting to change the
113.Vt DSA_METHOD
114for the key can have unexpected results.
115.Pp
116.Fn DSA_new_method
117allocates and initializes a
118.Vt DSA
119structure.
120The
121.Fa engine
122argument is ignored and
123the default method controlled by
124.Fn DSA_set_default_method
125is used.
126.Pp
127The
128.Vt DSA_METHOD
129structure is defined as follows:
130.Bd -literal
131struct {
132 /* name of the implementation */
133 const char *name;
134 /* sign */
135 DSA_SIG *(*dsa_do_sign)(const unsigned char *dgst, int dlen,
136 DSA *dsa);
137 /* pre-compute k^-1 and r */
138 int (*dsa_sign_setup)(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
139 BIGNUM **rp);
140 /* verify */
141 int (*dsa_do_verify)(const unsigned char *dgst, int dgst_len,
142 DSA_SIG *sig, DSA *dsa);
143 /* called at DSA_new */
144 int (*init)(DSA *DSA);
145 /* called at DSA_free */
146 int (*finish)(DSA *DSA);
147 int flags;
148} DSA_METHOD;
149.Ed
150.Sh RETURN VALUES
151.Fn DSA_OpenSSL
152and
153.Fn DSA_get_default_method
154return pointers to the respective
155.Vt DSA_METHOD .
156.Pp
157.Fn DSA_set_method
158returns 1 on success or 0 on failure.
159Currently, it cannot fail.
160.Pp
161.Fn DSA_new_method
162returns
163.Dv NULL
164and sets an error code that can be obtained by
165.Xr ERR_get_error 3
166if the allocation fails.
167Otherwise it returns a pointer to the newly allocated structure.
168.Sh SEE ALSO
169.Xr DSA_meth_new 3 ,
170.Xr DSA_new 3
171.Sh HISTORY
172.Fn DSA_set_default_method ,
173.Fn DSA_get_default_method ,
174.Fn DSA_set_method ,
175.Fn DSA_new_method ,
176and
177.Fn DSA_OpenSSL
178first appeared in OpenSSL 0.9.5 and have been available since
179.Ox 2.7 .