X25519

Section: OpenSSL (7)
Updated: 2021-03-26
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NAME

X25519, X448 - EVP_PKEY X25519 and X448 support

DESCRIPTION

The X25519 and X448 EVP_PKEY implementation supports key generation and key derivation using X25519 and X448. It has associated private and public key formats compatible with RFC 8410.

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.

NOTES

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

 EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_X25519, NULL);

For the X448 algorithm a context can be obtained by calling:

 EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_X448, NULL);

X25519 or X448 private keys can be set directly using EVP_PKEY_new_raw_private_key(3) or loaded from a PKCS#8 private key file using PEM_read_bio_PrivateKey(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.

X25519 or X448 public keys can be set directly using EVP_PKEY_new_raw_public_key(3) or loaded from a SubjectPublicKeyInfo structure in a PEM file using PEM_read_bio_PUBKEY(3) (or similar function).

EXAMPLES

This example generates an 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 EVP_PKEY_derive(3) can be used with X25519 and X448.

COPYRIGHT

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