X25519, X448 - EVP_PKEY X25519 and X448 support
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 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.
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).
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.
EVP_PKEY_CTX_new(3), EVP_PKEY_keygen(3), EVP_PKEY_derive(3), EVP_PKEY_derive_set_peer(3)
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