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.\" ========================================================================
.\"
.IX Title "DH_set_method 3"
.TH DH_set_method 3 "2020-12-10" "1.1.1i" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
DH_set_default_method, DH_get_default_method,
DH_set_method, DH_new_method, DH_OpenSSL \- select DH method
.SH "LIBRARY"
libcrypto, -lcrypto
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/dh.h>
\&
\& void DH_set_default_method(const DH_METHOD *meth);
\&
\& const DH_METHOD *DH_get_default_method(void);
\&
\& int DH_set_method(DH *dh, const DH_METHOD *meth);
\&
\& DH *DH_new_method(ENGINE *engine);
\&
\& const DH_METHOD *DH_OpenSSL(void);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
A \fB\s-1DH_METHOD\s0\fR specifies the functions that OpenSSL uses for Diffie-Hellman
operations. By modifying the method, alternative implementations
such as hardware accelerators may be used. \s-1IMPORTANT:\s0 See the \s-1NOTES\s0 section for
important information about how these \s-1DH API\s0 functions are affected by the use
of \fB\s-1ENGINE\s0\fR \s-1API\s0 calls.
.PP
Initially, the default \s-1DH_METHOD\s0 is the OpenSSL internal implementation, as
returned by \fBDH_OpenSSL()\fR.
.PP
\&\fBDH_set_default_method()\fR makes \fBmeth\fR the default method for all \s-1DH\s0
structures created later.
\&\fB\s-1NB\s0\fR: This is true only whilst no \s-1ENGINE\s0 has been set
as a default for \s-1DH,\s0 so this function is no longer recommended.
This function is not thread-safe and should not be called at the same time
as other OpenSSL functions.
.PP
\&\fBDH_get_default_method()\fR returns a pointer to the current default \s-1DH_METHOD.\s0
However, the meaningfulness of this result is dependent on whether the \s-1ENGINE
API\s0 is being used, so this function is no longer recommended.
.PP
\&\fBDH_set_method()\fR selects \fBmeth\fR to perform all operations using the key \fBdh\fR.
This will replace the \s-1DH_METHOD\s0 used by the \s-1DH\s0 key and if the previous method
was supplied by an \s-1ENGINE,\s0 the handle to that \s-1ENGINE\s0 will be released during the
change. It is possible to have \s-1DH\s0 keys that only work with certain \s-1DH_METHOD\s0
implementations (e.g. from an \s-1ENGINE\s0 module that supports embedded
hardware-protected keys), and in such cases attempting to change the \s-1DH_METHOD\s0
for the key can have unexpected results.
.PP
\&\fBDH_new_method()\fR allocates and initializes a \s-1DH\s0 structure so that \fBengine\fR will
be used for the \s-1DH\s0 operations. If \fBengine\fR is \s-1NULL,\s0 the default \s-1ENGINE\s0 for \s-1DH\s0
operations is used, and if no default \s-1ENGINE\s0 is set, the \s-1DH_METHOD\s0 controlled by
\&\fBDH_set_default_method()\fR is used.
.PP
A new \s-1DH_METHOD\s0 object may be constructed using \fBDH_meth_new()\fR (see
\&\fBDH_meth_new\fR\|(3)).
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBDH_OpenSSL()\fR and \fBDH_get_default_method()\fR return pointers to the respective
\&\fB\s-1DH_METHOD\s0\fRs.
.PP
\&\fBDH_set_default_method()\fR returns no value.
.PP
\&\fBDH_set_method()\fR returns nonzero if the provided \fBmeth\fR was successfully set as
the method for \fBdh\fR (including unloading the \s-1ENGINE\s0 handle if the previous
method was supplied by an \s-1ENGINE\s0).
.PP
\&\fBDH_new_method()\fR returns \s-1NULL\s0 and sets an error code that can be obtained by
\&\fBERR_get_error\fR\|(3) if the allocation fails. Otherwise it
returns a pointer to the newly allocated structure.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBDH_new\fR\|(3), \fBDH_new\fR\|(3), \fBDH_meth_new\fR\|(3)
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2000\-2020 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the OpenSSL license (the \*(L"License\*(R").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.