EVP_KEM-X25519(7SSL) OpenSSL EVP_KEM-X25519(7SSL)
NAME
EVP_KEM-X25519, EVP_KEM-X448 - EVP_KEM X25519 and EVP_KEM X448 keytype
and algorithm support
DESCRIPTION
The X25519 and <X448> keytype and its parameters are described in
EVP_PKEY-X25519(7). See EVP_PKEY_encapsulate(3) and
EVP_PKEY_decapsulate(3) for more info.
X25519 and X448 KEM parameters
"operation" (OSSL_KEM_PARAM_OPERATION)<UTF8 string>
The OpenSSL X25519 and X448 Key Encapsulation Mechanisms only
support the following default operation (operating mode):
"DHKEM" (OSSL_KEM_PARAM_OPERATION_DHKEM)
The encapsulate function generates an ephemeral keypair. It
produces keymaterial by doing an X25519 or X448 key exchange
using the ephemeral private key and a supplied recipient public
key. A HKDF operation using the keymaterial and a kem context
then produces a shared secret. The shared secret and the
ephemeral public key are returned. The decapsulate function
uses the recipient private key and the ephemeral public key to
produce the same keymaterial, which can then be used to produce
the same shared secret. See
<https://www.rfc-editor.org/rfc/rfc9180.html#name-dh-based-kem-dhkem>
This can be set using either EVP_PKEY_CTX_set_kem_op() or
EVP_PKEY_CTX_set_params().
"ikme" (OSSL_KEM_PARAM_IKME) <octet string>
Used to specify the key material used for generation of the
ephemeral key. This value should not be reused for other purposes.
It should have a length of at least 32 for X25519, and 56 for X448.
If this value is not set, then a random ikm is used.
CONFORMING TO
RFC9180
SEE ALSO
EVP_PKEY_CTX_set_kem_op(3), EVP_PKEY_encapsulate(3),
EVP_PKEY_decapsulate(3) EVP_KEYMGMT(3), EVP_PKEY(3), provider-keymgmt(7)
HISTORY
This functionality was added in OpenSSL 3.2.
The "operation" (operating mode) was a required parameter prior to
OpenSSL 3.5. As of OpenSSL 3.5, "DHKEM" is the default operating mode,
and no explicit value need be specified.
COPYRIGHT
Copyright 2022-2025 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>.
3.5.4 2025-09-30 EVP_KEM-X25519(7SSL)
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