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=head1 NAME

X25519 - EVP_PKEY X25519 support

=head1 DESCRIPTION

The B<X25519> EVP_PKEY implementation supports key generation and key
derivation using B<X25519>. It has associated private and public key formats
compatible with draft-ietf-curdle-pkix-03.

No additional parameters can be set during key generation.

The peer public key must be set using EVP_PKEY_derive_set_peer() when
performing key derivation.

=head1 NOTES

A context for the B<X25519> algorithm can be obtained by calling:

 EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_X25519, NULL);

=head1 EXAMPLE

This example generates an B<X25519> private key and writes it to standard
output in PEM format:

 #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);

The key derivation example in L<EVP_PKEY_derive(3)> can be used with
B<X25519>.

=head1 SEE ALSO

L<EVP_PKEY_CTX_new(3)>,
L<EVP_PKEY_keygen(3)>,
L<EVP_PKEY_derive(3)>,
L<EVP_PKEY_derive_set_peer(3)>

=head1 COPYRIGHT

Copyright 2017 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
L<https://www.openssl.org/source/license.html>.

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