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.\"
.IX Title "EVP_SIGNATURE-ED25519 7ossl"
.TH EVP_SIGNATURE-ED25519 7ossl "2026-01-27" "3.5.5" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH "NAME"
EVP_SIGNATURE\-ED25519,
EVP_SIGNATURE\-ED448,
Ed25519,
Ed448
\&\- EVP_PKEY Ed25519 and Ed448 support
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \fBEd25519\fR and \fBEd448\fR \s-1EVP_PKEY\s0 implementation supports key
generation, one-shot digest-sign and digest-verify using the EdDSA
signature schemes described in \s-1RFC 8032.\s0 It has associated private and
public key formats compatible with \s-1RFC 8410.\s0
.SS "EdDSA Instances"
.IX Subsection "EdDSA Instances"
\&\s-1RFC 8032\s0 describes five EdDSA instances: Ed25519, Ed25519ctx,
Ed25519ph, Ed448, Ed448ph.
.PP
The instances Ed25519, Ed25519ctx, Ed448 are referred to as \fBPureEdDSA\fR
schemes.  For these three instances, the sign and verify procedures
require access to the complete message (not a digest of the message).
.PP
The instances Ed25519ph, Ed448ph are referred to as \fBHashEdDSA\fR
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 \s-1SHA512.\s0  For
Ed448ph, the hash function is \s-1SHAKE256\s0 with an output length of 512
bits.
.PP
The instances Ed25519ctx, Ed25519ph, Ed448, Ed448ph accept an optional
\&\fBcontext-string\fR 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.
.PP
These instances can be specified as signature parameters when using
\&\fBEVP_DigestSignInit\fR\|(3) and \fBEVP_DigestVerifyInit\fR\|(3), see
\&\*(L"\s-1ED25519\s0 and \s-1ED448\s0 Signature Parameters\*(R" below.
.PP
These instances are also explicitly fetchable as algorithms using
\&\fBEVP_SIGNATURE_fetch\fR\|(3), which can be used with
\&\fBEVP_PKEY_sign_init_ex2\fR\|(3), \fBEVP_PKEY_verify_init_ex2\fR\|(3),
\&\fBEVP_PKEY_sign_message_init\fR\|(3) and \fBEVP_PKEY_verify_message_init\fR\|(3).
.SS "\s-1ED25519\s0 and \s-1ED448\s0 Signature Parameters"
.IX Subsection "ED25519 and ED448 Signature Parameters"
Two parameters can be set during signing or verification: the EdDSA
\&\fBinstance name\fR and the \fBcontext-string value\fR.  They can be set by
passing an \s-1OSSL_PARAM\s0 array to \fBEVP_DigestSignInit_ex()\fR.
.IP "\(bu" 4
\&\*(L"instance\*(R" (\fB\s-1OSSL_SIGNATURE_PARAM_INSTANCE\s0\fR) <utf8 string>
.Sp
One of the five strings \*(L"Ed25519\*(R", \*(L"Ed25519ctx\*(R", \*(L"Ed25519ph\*(R", \*(L"Ed448\*(R", \*(L"Ed448ph\*(R".
.Sp
\&\*(L"Ed25519\*(R", \*(L"Ed25519ctx\*(R", \*(L"Ed25519ph\*(R" are valid only for an Ed25519 \s-1EVP_PKEY.\s0
.Sp
\&\*(L"Ed448\*(R", \*(L"Ed448ph\*(R" are valid only for an Ed448 \s-1EVP_PKEY.\s0
.IP "\(bu" 4
\&\*(L"context-string\*(R" (\fB\s-1OSSL_SIGNATURE_PARAM_CONTEXT_STRING\s0\fR) <octet string>
.Sp
A string of octets with length at most 255.
.PP
Both of these parameters are optional.
.PP
When using \fBEVP_DigestSignInit\fR\|(3) or \fBEVP_DigestVerifyInit\fR\|(3), the
signature algorithm is derived from the key type name.  The key type name
(\*(L"Ed25519\*(R" or \*(L"Ed448\*(R") is also the default for the instance, but this can be
changed with the \*(L"instance\*(R" parameter.
.PP
Note that a message digest name must \fB\s-1NOT\s0\fR be specified when signing
or verifying.
.PP
When using \fBEVP_PKEY_sign_init_ex2\fR\|(3), \fBEVP_PKEY_verify_init_ex2\fR\|(3),
\&\fBEVP_PKEY_sign_message_init\fR\|(3) or \fBEVP_PKEY_verify_message_init\fR\|(3), the
instance is the explicit signature algorithm name, and may not be changed
(trying to give one with the \*(L"instance\*(R" parameter is therefore an error).
.PP
If a context-string is not specified, then an empty context-string is
used.
.PP
See \s-1\fBEVP_PKEY\-X25519\s0\fR\|(7) for information related to \fBX25519\fR and \fBX448\fR keys.
.PP
The following signature parameters can be retrieved using
\&\fBEVP_PKEY_CTX_get_params()\fR.
.IP "\(bu" 4
\&\*(L"algorithm-id\*(R" (\fB\s-1OSSL_SIGNATURE_PARAM_ALGORITHM_ID\s0\fR) <octet string>
.IP "\(bu" 4
\&\*(L"instance\*(R" (\fB\s-1OSSL_SIGNATURE_PARAM_INSTANCE\s0\fR) <utf8 string>
.IP "\(bu" 4
\&\*(L"context-string\*(R" (\fB\s-1OSSL_SIGNATURE_PARAM_CONTEXT_STRING\s0\fR) <octet string>
.PP
The parameters are described in \fBprovider\-signature\fR\|(7).
.SH "NOTES"
.IX Header "NOTES"
The PureEdDSA instances do not support the streaming mechanism of
other signature algorithms using, for example, \fBEVP_DigestUpdate()\fR.
The message to sign or verify must be passed using the one-shot
\&\fBEVP_DigestSign()\fR and \fBEVP_DigestVerify()\fR functions.
.PP
The HashEdDSA instances do not yet support the streaming mechanisms
(so the one-shot functions must be used with HashEdDSA as well).
.PP
When calling \fBEVP_DigestSignInit()\fR or \fBEVP_DigestVerifyInit()\fR, the
digest \fItype\fR parameter \fB\s-1MUST\s0\fR be set to \s-1NULL.\s0
.PP
Applications wishing to sign certificates (or other structures such as
CRLs or certificate requests) using Ed25519 or Ed448 can either use \fBX509_sign()\fR
or \fBX509_sign_ctx()\fR in the usual way.
.PP
Ed25519 or Ed448 private keys can be set directly using
\&\fBEVP_PKEY_new_raw_private_key\fR\|(3) or loaded from a PKCS#8 private key file
using \fBPEM_read_bio_PrivateKey\fR\|(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.
.PP
Ed25519 or Ed448 public keys can be set directly using
\&\fBEVP_PKEY_new_raw_public_key\fR\|(3) or loaded from a SubjectPublicKeyInfo
structure in a \s-1PEM\s0 file using \fBPEM_read_bio_PUBKEY\fR\|(3) (or similar function).
.PP
Ed25519 and Ed448 can be tested with the \fBopenssl\-speed\fR\|(1) application
since version 1.1.1.
Valid algorithm names are \fBed25519\fR, \fBed448\fR and \fBeddsa\fR. If \fBeddsa\fR is
specified, then both Ed25519 and Ed448 are benchmarked.
.PP
Since Ed25519ctx is not included in \s-1FIPS 186\-5,\s0 it is not present
in the \s-1FIPS\s0 provider.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
To sign a message using an \s-1ED25519 EVP_PKEY\s0 structure:
.PP
.Vb 5
\&    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);
\&    }
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\s-1\fBEVP_PKEY\-X25519\s0\fR\|(7)
\&\fBprovider\-signature\fR\|(7),
\&\fBEVP_DigestSignInit\fR\|(3),
\&\fBEVP_DigestVerifyInit\fR\|(3),
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2017\-2024 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the Apache License 2.0 (the \*(L"License\*(R").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.
