=pod
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=head1 NAME
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X25519,
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X448
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- EVP_PKEY X25519 and X448 support
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=head1 DESCRIPTION
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The B<X25519> and B<X448> EVP_PKEY implementation supports key generation and
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key derivation using B<X25519> and B<X448>. It has associated private and public
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key formats compatible with RFC 8410.
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No additional parameters can be set during key generation.
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The peer public key must be set using EVP_PKEY_derive_set_peer() when
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performing key derivation.
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=head1 NOTES
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A context for the B<X25519> algorithm can be obtained by calling:
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EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_X25519, NULL);
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For the B<X448> algorithm a context can be obtained by calling:
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EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_X448, NULL);
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X25519 or X448 private keys can be set directly using
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L<EVP_PKEY_new_raw_private_key(3)> or loaded from a PKCS#8 private key file
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using L<PEM_read_bio_PrivateKey(3)> (or similar function). Completely new keys
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can also be generated (see the example below). Setting a private key also sets
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the associated public key.
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X25519 or X448 public keys can be set directly using
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L<EVP_PKEY_new_raw_public_key(3)> or loaded from a SubjectPublicKeyInfo
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structure in a PEM file using L<PEM_read_bio_PUBKEY(3)> (or similar function).
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=head1 EXAMPLES
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This example generates an B<X25519> private key and writes it to standard
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output in PEM format:
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#include <openssl/evp.h>
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#include <openssl/pem.h>
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...
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EVP_PKEY *pkey = NULL;
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EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_X25519, NULL);
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EVP_PKEY_keygen_init(pctx);
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EVP_PKEY_keygen(pctx, &pkey);
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EVP_PKEY_CTX_free(pctx);
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PEM_write_PrivateKey(stdout, pkey, NULL, NULL, 0, NULL, NULL);
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The key derivation example in L<EVP_PKEY_derive(3)> can be used with
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B<X25519> and B<X448>.
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=head1 SEE ALSO
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L<EVP_PKEY_CTX_new(3)>,
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L<EVP_PKEY_keygen(3)>,
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L<EVP_PKEY_derive(3)>,
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L<EVP_PKEY_derive_set_peer(3)>
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=head1 COPYRIGHT
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Copyright 2017-2020 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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