X25519(7SSL)

📦
version 4.0.3 · 13 versions
, in ubuntu stonking

💖 X25519 — the OpenSSL manual, but make it make sense 💖

okay bestie, sit DOWN, because we're talking about X25519, X448, and the EVP_PKEY support that makes them go brrr. this is X25519(7SSL) from the OpenSSL fam, and by the end of this page you're gonna be the main character of elliptic-curve key exchange. no cap. 🔥

✨ NAME ✨

X25519, X448 — the whole EVP_PKEY X25519 and X448 support situation 💅

🌸 DESCRIPTION 🌸

so the X25519 and X448 EVP_PKEY implementation does two (2) iconic things: key generation and key derivation, using X25519 and X448. it also ships with associated private and public key formats that are compatible with RFC 8410. we love a standards-compliant queen. 🎀

heads up: no additional parameters can be set during key generation. that's just not a thing here, bestie, don't try it.

also, when you're doing key derivation, the peer public key must be set using EVP_PKEY_derive_set_peer(). you can't skip that step, it's giving mandatory. 🫶

🦋 NOTES 🦋

want a context for the X25519 algorithm? literally just call:

EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_X25519, NULL);

and for the X448 algorithm, you get a context by calling:

EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_X448, NULL);

okay so how do you get keys in there? multiple ways, pick your fighter:

  • 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 a similar function). and completely new keys can also be generated — peep the example below 👀
  • the way that setting a private key also sets the associated public key?? so convenient, obsessed. 💜
  • 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 a similar function). periodt.

🌈 EXAMPLES 🌈

this example generates an X25519 private key and writes it to standard output in PEM format. it's giving minimal, it's giving effective:

#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);

and if you're here for derivation? the key derivation example over in EVP_PKEY_derive(3) can be used with X25519 and X448. reusing examples is self-care fr fr. ✨

💀 SEE ALSO 💀

Copyright 2017-2020 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (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>.

and that's the whole page, bestie 🎀 this was X25519(7SSL) from OpenSSL 4.0.3, dated 2026-09-29 — go forth and derive those shared secrets, you absolute icon 💖✨🌺

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