EVP_SIGNATURE-ED25519(7SSL)

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version 4.0.3 · 13 versions
, in ubuntu stonking

💖 EVP_SIGNATURE-ED25519 — the OpenSSL manual, but make it slay ✨

okay bestie, come sit with me because this one is so good. this is the manual page for EVP_SIGNATURE-ED25519, EVP_SIGNATURE-ED448, Ed25519 and Ed448 — the signature implementations inside OpenSSL. yes, that OpenSSL. the big one. let's go 💅

🌸 NAME 🌸

EVP_SIGNATURE-ED25519, EVP_SIGNATURE-ED448, Ed25519, Ed448 — the EVP_PKEY Ed25519 and Ed448 signature implementations. that's the whole vibe. no notes. 👑

🦋 DESCRIPTION 🦋

so 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 also has associated private and public key formats compatible with RFC 8410.

periodt. ✨

🎀 EdDSA Instances 🎀

RFC 8032 describes five EdDSA instances: Ed25519, Ed25519ctx, Ed25519ph, Ed448, Ed448ph. five of them. a whole girl group. 🌈

The instances Ed25519, Ed25519ctx, Ed448 are referred to as PureEdDSA schemes. for these three, the sign and verify procedures require access to the complete message — not a digest of the message. like, the whole entire message. no cutting corners 💅

The instances Ed25519ph, Ed448ph are referred to as HashEdDSA schemes. for these two, 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. iconic behaviour, honestly.

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 — no empty vibes allowed for her). 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). so many entry points, she's versatile 🫶

💜 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. yes bestie, optional. breathe. 😌

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. not optional. do not. 💀

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 — so trying to give one with the "instance" parameter is therefore an error. she said no. 🙈

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>
  • "fips-indicator" (OSSL_SIGNATURE_PARAM_FIPS_APPROVED_INDICATOR) <integer> — the OpenSSL FIPS provider returns 1 if the operation is FIPS approved, or 0 otherwise. see "FIPS indicators" in fips_module(7) for more information.

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. one shot, no drip. 💅

The HashEdDSA instances do not yet support the streaming mechanisms — so the one-shot functions must be used with HashEdDSA as well. (yet!! the girlies are working on it probably, but that's what the page says, don't come for me 🍓)

When calling EVP_DigestSignInit() or EVP_DigestVerifyInit(), the digest type parameter MUST be set to NULL. all caps, bestie. it's serious. 😭

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. two for one, we love efficiency ✨

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. speedrun both queens 🏃‍♀️

Since Ed25519ctx is not included in FIPS 186-5, it is not present in the FIPS provider. sorry to that girl, she didn't make the list 🥲

🔥 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);
}

look at her go 😭💖

🫶 SEE ALSO 🫶

EVP_PKEY-X25519(7) provider-signature(7), EVP_DigestSignInit(3), EVP_DigestVerifyInit(3),

Copyright 2017-2026 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 OpenSSL 4.0.3, dated 2026-09-29, and she ate every single time 💅✨ no cap. now go sign something 🦋💖

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