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.\" ========================================================================
.\"
.IX Title "X25519 7"
.TH X25519 7 "2023-09-11" "1.1.1w" "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"
X25519, X448 \&\- EVP_PKEY X25519 and X448 support
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \fBX25519\fR and \fBX448\fR \s-1EVP_PKEY\s0 implementation supports key generation and
key derivation using \fBX25519\fR and \fBX448\fR. It has associated private and public
key formats compatible with \s-1RFC 8410.\s0
.PP
No additional parameters can be set during key generation.
.PP
The peer public key must be set using \fBEVP_PKEY_derive_set_peer()\fR when
performing key derivation.
.SH "NOTES"
.IX Header "NOTES"
A context for the \fBX25519\fR algorithm can be obtained by calling:
.PP
.Vb 1
\& EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_X25519, NULL);
.Ve
.PP
For the \fBX448\fR algorithm a context can be obtained by calling:
.PP
.Vb 1
\& EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_X448, NULL);
.Ve
.PP
X25519 or X448 private keys can be set directly using
\&\fBEVP_PKEY_new_raw_private_key\fR\|(3) or loaded from a PKCS#8 private key file
using \fBPEM_read_bio_PrivateKey\fR\|(3) (or similar function). Completely new keys
can also be generated (see the example below). Setting a private key also sets
the associated public key.
.PP
X25519 or X448 public keys can be set directly using
\&\fBEVP_PKEY_new_raw_public_key\fR\|(3) or loaded from a SubjectPublicKeyInfo
structure in a \s-1PEM\s0 file using \fBPEM_read_bio_PUBKEY\fR\|(3) (or similar function).
.SH "EXAMPLES"
.IX Header "EXAMPLES"
This example generates an \fBX25519\fR private key and writes it to standard
output in \s-1PEM\s0 format:
.PP
.Vb 9
\& #include <openssl/evp.h>
\& #include <openssl/pem.h>
\& ...
\& EVP_PKEY *pkey = NULL;
\& EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_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);
.Ve
.PP
The key derivation example in \fBEVP_PKEY_derive\fR\|(3) can be used with
\&\fBX25519\fR and \fBX448\fR.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBEVP_PKEY_CTX_new\fR\|(3),
\&\fBEVP_PKEY_keygen\fR\|(3),
\&\fBEVP_PKEY_derive\fR\|(3),
\&\fBEVP_PKEY_derive_set_peer\fR\|(3)
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2017\-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>.

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