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.IX Title "DH_SET_METHOD 3ossl"
.TH DH_SET_METHOD 3ossl 2026-09-29 4.0.3 OpenSSL
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.nh
.SH NAME
DH_set_default_method, DH_get_default_method,
DH_set_method, DH_new_method, DH_OpenSSL \- select DH method
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/dh.h>
.Ve
.PP
The following functions have been deprecated since OpenSSL 3.0, and can be
hidden entirely by defining \fBOPENSSL_API_COMPAT\fR with a suitable version value,
see \fBopenssl_user_macros\fR\|(7):
.PP
.Vb 1
\& 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"
All of the functions described on this page are deprecated.
Applications should instead use the provider APIs.
.PP
A \fBDH_METHOD\fR specifies the functions that OpenSSL uses for Diffie\-Hellman
operations. By modifying the method, alternative implementations
such as hardware accelerators may be used.
.PP
Initially, the default DH_METHOD 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 DH
structures created later.
\&\fBNB\fR:
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 DH_METHOD.
.PP
\&\fBDH_set_method()\fR selects \fBmeth\fR to perform all operations using the key
\&\fBdh\fR. This will replace the DH_METHOD used by the DH key.
It is possible to have DH keys that only work with certain DH_METHOD
implementations, and in such cases attempting to change the DH_METHOD for the
key can have unexpected results. See \fBDH_meth_new\fR\|(3) for information on
constructing custom DH_METHOD objects.
.PP
\&\fBDH_new_method()\fR allocates and initializes a DH structure. \fBengine\fR must
be NULL and the DH_METHOD controlled by \fBDH_set_default_method()\fR is used.
.PP
A new DH_METHOD 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
\&\fBDH_METHOD\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.
.PP
\&\fBDH_new_method()\fR returns NULL 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 HISTORY
.IX Header "HISTORY"
All of these functions were deprecated in OpenSSL 3.0.
.SH COPYRIGHT
.IX Header "COPYRIGHT"
Copyright 2000\-2025 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the Apache License 2.0 (the "License").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.