EVP_SIGNATURE-ED25519(7SSL) OpenSSL EVP_SIGNATURE-ED25519(7SSL)
NAME
EVP_SIGNATURE-ED25519, EVP_SIGNATURE-ED448, Ed25519, Ed448 - EVP_PKEY
Ed25519 and Ed448 support
DESCRIPTION
The Ed25519 and Ed448 EVP_PKEY implementation supports key generation,
one-shot digest-sign and digest-verify using the EdDSA signature schemes
described in RFC 8032. It has associated private and public key formats
compatible with RFC 8410.
EdDSA Instances
RFC 8032 describes five EdDSA instances: Ed25519, Ed25519ctx, Ed25519ph,
Ed448, Ed448ph.
The instances Ed25519, Ed25519ctx, Ed448 are referred to as PureEdDSA
schemes. For these three instances, the sign and verify procedures
require access to the complete message (not a digest of the message).
The instances Ed25519ph, Ed448ph are referred to as HashEdDSA schemes.
For these two instances, the sign and verify procedures do not require
access to the complete message; they operate on a hash of the message.
For Ed25519ph, the hash function is SHA512. For Ed448ph, the hash
function is SHAKE256 with an output length of 512 bits.
The instances Ed25519ctx, Ed25519ph, Ed448, Ed448ph accept an optional
context-string as input to sign and verify operations (and for
Ed25519ctx, the context-string must be nonempty). For the Ed25519
instance, a nonempty context-string is not permitted.
These instances can be specified as signature parameters when using
EVP_DigestSignInit(3) and EVP_DigestVerifyInit(3), see "ED25519 and
ED448 Signature Parameters" below.
These instances are also explicitly fetchable as algorithms using
EVP_SIGNATURE_fetch(3), which can be used with
EVP_PKEY_sign_init_ex2(3), EVP_PKEY_verify_init_ex2(3),
EVP_PKEY_sign_message_init(3) and EVP_PKEY_verify_message_init(3).
ED25519 and ED448 Signature Parameters
Two parameters can be set during signing or verification: the EdDSA
instance name and the context-string value. They can be set by passing
an OSSL_PARAM array to EVP_DigestSignInit_ex().
• "instance" (OSSL_SIGNATURE_PARAM_INSTANCE) <utf8 string>
One of the five strings "Ed25519", "Ed25519ctx", "Ed25519ph",
"Ed448", "Ed448ph".
"Ed25519", "Ed25519ctx", "Ed25519ph" are valid only for an Ed25519
EVP_PKEY.
"Ed448", "Ed448ph" are valid only for an Ed448 EVP_PKEY.
• "context-string" (OSSL_SIGNATURE_PARAM_CONTEXT_STRING) <octet
string>
A string of octets with length at most 255.
Both of these parameters are optional.
When using EVP_DigestSignInit(3) or EVP_DigestVerifyInit(3), the
signature algorithm is derived from the key type name. The key type
name ("Ed25519" or "Ed448") is also the default for the instance, but
this can be changed with the "instance" parameter.
Note that a message digest name must NOT be specified when signing or
verifying.
When using EVP_PKEY_sign_init_ex2(3), EVP_PKEY_verify_init_ex2(3),
EVP_PKEY_sign_message_init(3) or EVP_PKEY_verify_message_init(3), the
instance is the explicit signature algorithm name, and may not be
changed (trying to give one with the "instance" parameter is therefore
an error).
If a context-string is not specified, then an empty context-string is
used.
See EVP_PKEY-X25519(7) for information related to X25519 and X448 keys.
The following signature parameters can be retrieved using
EVP_PKEY_CTX_get_params().
• "algorithm-id" (OSSL_SIGNATURE_PARAM_ALGORITHM_ID) <octet string>
• "instance" (OSSL_SIGNATURE_PARAM_INSTANCE) <utf8 string>
• "context-string" (OSSL_SIGNATURE_PARAM_CONTEXT_STRING) <octet
string>
The parameters are described in provider-signature(7).
NOTES
The PureEdDSA instances do not support the streaming mechanism of other
signature algorithms using, for example, EVP_DigestUpdate(). The
message to sign or verify must be passed using the one-shot
EVP_DigestSign() and EVP_DigestVerify() functions.
The HashEdDSA instances do not yet support the streaming mechanisms (so
the one-shot functions must be used with HashEdDSA as well).
When calling EVP_DigestSignInit() or EVP_DigestVerifyInit(), the digest
type parameter MUST be set to NULL.
Applications wishing to sign certificates (or other structures such as
CRLs or certificate requests) using Ed25519 or Ed448 can either use
X509_sign() or X509_sign_ctx() in the usual way.
Ed25519 or Ed448 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.
Ed25519 or Ed448 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).
Ed25519 and Ed448 can be tested with the openssl-speed(1) application
since version 1.1.1. Valid algorithm names are ed25519, ed448 and
eddsa. If eddsa is specified, then both Ed25519 and Ed448 are
benchmarked.
EXAMPLES
To sign a message using an ED25519 EVP_PKEY structure:
void do_sign(EVP_PKEY *ed_key, unsigned char *msg, size_t msg_len)
{
size_t sig_len;
unsigned char *sig = NULL;
EVP_MD_CTX *md_ctx = EVP_MD_CTX_new();
const OSSL_PARAM params[] = {
OSSL_PARAM_utf8_string ("instance", "Ed25519ctx", 10),
OSSL_PARAM_octet_string("context-string", (unsigned char *)"A protocol defined context string", 33),
OSSL_PARAM_END
};
/* The input "params" is not needed if default options are acceptable.
Use NULL in place of "params" in that case. */
EVP_DigestSignInit_ex(md_ctx, NULL, NULL, NULL, NULL, ed_key, params);
/* Calculate the required size for the signature by passing a NULL buffer. */
EVP_DigestSign(md_ctx, NULL, &sig_len, msg, msg_len);
sig = OPENSSL_zalloc(sig_len);
EVP_DigestSign(md_ctx, sig, &sig_len, msg, msg_len);
...
OPENSSL_free(sig);
EVP_MD_CTX_free(md_ctx);
}
SEE ALSO
EVP_PKEY-X25519(7) provider-signature(7), EVP_DigestSignInit(3),
EVP_DigestVerifyInit(3),
COPYRIGHT
Copyright 2017-2024 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_SIGNATURE-ED25519(7SSL)
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