.\" $OpenBSD: DH_set_method.3,v 1.8 2022/01/15 23:38:50 jsg Exp $ .\" OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100 .\" .\" This file was written by Ulf Moeller . .\" Copyright (c) 2000, 2002, 2007 The OpenSSL Project. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in .\" the documentation and/or other materials provided with the .\" distribution. .\" .\" 3. All advertising materials mentioning features or use of this .\" software must display the following acknowledgment: .\" "This product includes software developed by the OpenSSL Project .\" for use in the OpenSSL Toolkit. 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IN NO EVENT SHALL THE OpenSSL PROJECT OR .\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, .\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; .\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, .\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED .\" OF THE POSSIBILITY OF SUCH DAMAGE. .\" .Dd $Mdocdate: January 15 2022 $ .Dt DH_SET_METHOD 3 .Os .Sh NAME .Nm DH_set_default_method , .Nm DH_get_default_method , .Nm DH_set_method , .Nm DH_new_method , .Nm DH_OpenSSL .Nd select DH method .Sh SYNOPSIS .In openssl/dh.h .Ft void .Fo DH_set_default_method .Fa "const DH_METHOD *meth" .Fc .Ft const DH_METHOD * .Fo DH_get_default_method .Fa void .Fc .Ft int .Fo DH_set_method .Fa "DH *dh" .Fa "const DH_METHOD *meth" .Fc .Ft DH * .Fo DH_new_method .Fa "ENGINE *engine" .Fc .Ft const DH_METHOD * .Fo DH_OpenSSL .Fa void .Fc .Sh DESCRIPTION A .Vt DH_METHOD object contains pointers to the functions used for Diffie-Hellman operations. By default, the internal implementation returned by .Fn DH_OpenSSL is used. By selecting another method, alternative implementations such as hardware accelerators may be used. .Pp .Fn DH_set_default_method selects .Fa meth as the default method for all .Vt DH structures created later. If any .Vt ENGINE was registered with .Xr ENGINE_register_DH 3 that can be successfully initialized, it overrides the default. .Pp .Fn DH_get_default_method returns a pointer to the current default method, even if it is actually overridden by an .Vt ENGINE . .Pp .Fn DH_set_method selects .Fa meth to perform all operations using the key .Fa dh . This replaces the .Vt DH_METHOD used by the .Fa dh key and if the previous method was supplied by an .Vt ENGINE , .Xr ENGINE_finish 3 is called on it. It is possible to have .Vt DH keys that only work with certain .Vt DH_METHOD implementations (e.g. from an .Vt ENGINE module that supports embedded hardware-protected keys), and in such cases attempting to change the .Vt DH_METHOD for the key can have unexpected results. .Pp .Fn DH_new_method allocates and initializes a .Vt DH structure so that .Fa engine is used for the DH operations. If .Fa engine is .Dv NULL , .Xr ENGINE_get_default_DH 3 is used. If that returns .Dv NULL , the default method controlled by .Fn DH_set_default_method is used. .Pp The .Vt DH_METHOD structure is defined as follows: .Bd -literal typedef struct dh_meth_st { /* name of the implementation */ const char *name; /* generate private and public DH values for key agreement */ int (*generate_key)(DH *dh); /* compute shared secret */ int (*compute_key)(unsigned char *key, BIGNUM *pub_key, DH *dh); /* compute r = a ^ p mod m (May be NULL for some implementations) */ int (*bn_mod_exp)(DH *dh, BIGNUM *r, BIGNUM *a, const BIGNUM *p, const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx); /* called at DH_new */ int (*init)(DH *dh); /* called at DH_free */ int (*finish)(DH *dh); int flags; char *app_data; /* ?? */ } DH_METHOD; .Ed .Sh RETURN VALUES .Fn DH_OpenSSL and .Fn DH_get_default_method return pointers to the respective .Vt DH_METHOD . .Pp .Fn DH_set_method returns 1 on success or 0 on failure. Currently, it cannot fail. .Pp .Fn DH_new_method returns .Dv NULL and sets an error code that can be obtained by .Xr ERR_get_error 3 if the allocation fails. Otherwise it returns a pointer to the newly allocated structure. .Sh SEE ALSO .Xr DH_new 3 , .Xr ENGINE_get_default_DH 3 , .Xr ENGINE_register_DH 3 , .Xr ENGINE_set_default_DH 3 .Sh HISTORY .Fn DH_set_default_method , .Fn DH_get_default_method , .Fn DH_set_method , .Fn DH_new_method and .Fn DH_OpenSSL first appeared in OpenSSL 0.9.5 and have been available since .Ox 2.7 .