NAME

       DH_set_default_method, DH_get_default_method, DH_set_method, DH_new_method, DH_OpenSSL -
       select DH method

SYNOPSIS

        #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);

DESCRIPTION

       A DH_METHOD specifies the functions that OpenSSL uses for Diffie-Hellman operations. By
       modifying the method, alternative implementations such as hardware accelerators may be
       used. IMPORTANT: See the NOTES section for important information about how these DH API
       functions are affected by the use of ENGINE API calls.

       Initially, the default DH_METHOD is the OpenSSL internal implementation, as returned by
       DH_OpenSSL().

       DH_set_default_method() makes meth the default method for all DH structures created later.
       NB: This is true only whilst no ENGINE has been set as a default for DH, 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.

       DH_get_default_method() returns a pointer to the current default DH_METHOD.  However, the
       meaningfulness of this result is dependent on whether the ENGINE API is being used, so
       this function is no longer recommended.

       DH_set_method() selects meth to perform all operations using the key dh.  This will
       replace the DH_METHOD used by the DH key and if the previous method was supplied by an
       ENGINE, the handle to that ENGINE will be released during the change. It is possible to
       have DH keys that only work with certain DH_METHOD implementations (eg. from an ENGINE
       module that supports embedded hardware-protected keys), and in such cases attempting to
       change the DH_METHOD for the key can have unexpected results.

       DH_new_method() allocates and initializes a DH structure so that engine will be used for
       the DH operations. If engine is NULL, the default ENGINE for DH operations is used, and if
       no default ENGINE is set, the DH_METHOD controlled by DH_set_default_method() is used.

       A new DH_METHOD object may be constructed using DH_meth_new() (see DH_meth_new(3)).

RETURN VALUES

       DH_OpenSSL() and DH_get_default_method() return pointers to the respective DH_METHODs.

       DH_set_default_method() returns no value.

       DH_set_method() returns non-zero if the provided meth was successfully set as the method
       for dh (including unloading the ENGINE handle if the previous method was supplied by an
       ENGINE).

       DH_new_method() returns NULL and sets an error code that can be obtained by
       ERR_get_error(3) if the allocation fails. Otherwise it returns a pointer to the newly
       allocated structure.

SEE ALSO

       DH_new(3), DH_new(3), DH_meth_new(3)

COPYRIGHT

       Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the OpenSSL license (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>.