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.\" $OpenBSD: X25519.3,v 1.1 2017/04/10 17:45:06 schwarze Exp $
.\" OpenSSL X25519.pod 69687aa8 Mar 28 23:57:28 2017 +0200
.\"
.\" This file was written by Dr. Stephen Henson <steve@openssl.org>.
.\" Copyright (c) 2017 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. (http://www.openssl.org/)"
.\"
.\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
.\" endorse or promote products derived from this software without
.\" prior written permission. For written permission, please contact
.\" openssl-core@openssl.org.
.\"
.\" 5. Products derived from this software may not be called "OpenSSL"
.\" nor may "OpenSSL" appear in their names without prior written
.\" permission of the OpenSSL Project.
.\"
.\" 6. Redistributions of any form whatsoever must retain the following
.\" acknowledgment:
.\" "This product includes software developed by the OpenSSL Project
.\" for use in the OpenSSL Toolkit (http://www.openssl.org/)"
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED. 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,
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
.\" OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd $Mdocdate: April 10 2017 $
.Dt X25519 3
.Os
.Sh NAME
.Nm X25519
.Nd EVP_PKEY X25519 support
.Sh DESCRIPTION
The
.Nm
.Vt EVP_PKEY
implementation supports key generation and key derivation using X25519.
It has associated private and public key formats compatible with
draft-ietf-curdle-pkix-03.
.Pp
No additional parameters can be set during key generation.
.Pp
The peer public key must be set using
.Xr EVP_PKEY_derive_set_peer 3
when performing key derivation.
.Pp
A context for the
.Nm
algorithm can be obtained by calling:
.Pp
.Dl EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(NID_X25519, NULL);
.Sh EXAMPLES
Generate an
.Nm
private key and write it to standard output in PEM format:
.Bd -literal
#include <openssl/evp.h>
#include <openssl/pem.h>
EVP_PKEY *pkey = NULL;
EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(NID_X25519, NULL);
EVP_PKEY_keygen_init(pctx);
EVP_PKEY_keygen(pctx, &pkey);
EVP_PKEY_CTX_free(pctx);
PEM_write_PrivateKey(stdout, pkey, NULL, NULL, 0, NULL, NULL);
.Ed
.Pp
The key derivation example in
.Xr EVP_PKEY_derive 3
can be used with
.Nm .
.Sh SEE ALSO
.Xr EVP_PKEY_CTX_new 3 ,
.Xr EVP_PKEY_derive 3 ,
.Xr EVP_PKEY_keygen 3
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