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133 .\" ========================================================================
135 .IX Title "DH_SET_METHOD 3"
136 .TH DH_SET_METHOD 3 "2020-03-31" "1.1.1f" "OpenSSL"
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142 DH_set_default_method, DH_get_default_method, DH_set_method, DH_new_method, DH_OpenSSL \- select DH method
144 .IX Header "SYNOPSIS"
146 \& #include <openssl/dh.h>
148 \& void DH_set_default_method(const DH_METHOD *meth);
150 \& const DH_METHOD *DH_get_default_method(void);
152 \& int DH_set_method(DH *dh, const DH_METHOD *meth);
154 \& DH *DH_new_method(ENGINE *engine);
156 \& const DH_METHOD *DH_OpenSSL(void);
159 .IX Header "DESCRIPTION"
160 A \fB\s-1DH_METHOD\s0\fR specifies the functions that OpenSSL uses for Diffie-Hellman
161 operations. By modifying the method, alternative implementations
162 such as hardware accelerators may be used. \s-1IMPORTANT:\s0 See the \s-1NOTES\s0 section for
163 important information about how these \s-1DH API\s0 functions are affected by the use
164 of \fB\s-1ENGINE\s0\fR \s-1API\s0 calls.
166 Initially, the default \s-1DH_METHOD\s0 is the OpenSSL internal implementation, as
167 returned by \fBDH_OpenSSL()\fR.
169 \&\fBDH_set_default_method()\fR makes \fBmeth\fR the default method for all \s-1DH\s0
170 structures created later.
171 \&\fB\s-1NB\s0\fR: This is true only whilst no \s-1ENGINE\s0 has been set
172 as a default for \s-1DH,\s0 so this function is no longer recommended.
173 This function is not thread-safe and should not be called at the same time
174 as other OpenSSL functions.
176 \&\fBDH_get_default_method()\fR returns a pointer to the current default \s-1DH_METHOD.\s0
177 However, the meaningfulness of this result is dependent on whether the \s-1ENGINE
178 API\s0 is being used, so this function is no longer recommended.
180 \&\fBDH_set_method()\fR selects \fBmeth\fR to perform all operations using the key \fBdh\fR.
181 This will replace the \s-1DH_METHOD\s0 used by the \s-1DH\s0 key and if the previous method
182 was supplied by an \s-1ENGINE,\s0 the handle to that \s-1ENGINE\s0 will be released during the
183 change. It is possible to have \s-1DH\s0 keys that only work with certain \s-1DH_METHOD\s0
184 implementations (eg. from an \s-1ENGINE\s0 module that supports embedded
185 hardware-protected keys), and in such cases attempting to change the \s-1DH_METHOD\s0
186 for the key can have unexpected results.
188 \&\fBDH_new_method()\fR allocates and initializes a \s-1DH\s0 structure so that \fBengine\fR will
189 be used for the \s-1DH\s0 operations. If \fBengine\fR is \s-1NULL,\s0 the default \s-1ENGINE\s0 for \s-1DH\s0
190 operations is used, and if no default \s-1ENGINE\s0 is set, the \s-1DH_METHOD\s0 controlled by
191 \&\fBDH_set_default_method()\fR is used.
193 A new \s-1DH_METHOD\s0 object may be constructed using \fBDH_meth_new()\fR (see
194 \&\fBDH_meth_new\fR\|(3)).
196 .IX Header "RETURN VALUES"
197 \&\fBDH_OpenSSL()\fR and \fBDH_get_default_method()\fR return pointers to the respective
198 \&\fB\s-1DH_METHOD\s0\fRs.
200 \&\fBDH_set_default_method()\fR returns no value.
202 \&\fBDH_set_method()\fR returns non-zero if the provided \fBmeth\fR was successfully set as
203 the method for \fBdh\fR (including unloading the \s-1ENGINE\s0 handle if the previous
204 method was supplied by an \s-1ENGINE\s0).
206 \&\fBDH_new_method()\fR returns \s-1NULL\s0 and sets an error code that can be obtained by
207 \&\fBERR_get_error\fR\|(3) if the allocation fails. Otherwise it
208 returns a pointer to the newly allocated structure.
210 .IX Header "SEE ALSO"
211 \&\fBDH_new\fR\|(3), \fBDH_new\fR\|(3), \fBDH_meth_new\fR\|(3)
213 .IX Header "COPYRIGHT"
214 Copyright 2000\-2016 The OpenSSL Project Authors. All Rights Reserved.
216 Licensed under the OpenSSL license (the \*(L"License\*(R"). You may not use
217 this file except in compliance with the License. You can obtain a copy
218 in the file \s-1LICENSE\s0 in the source distribution or at
219 <https://www.openssl.org/source/license.html>.