script/dom/subtlecrypto/

ed25519_operation.rs

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */

use aws_lc_rs::encoding::{AsBigEndian, AsDer};
use aws_lc_rs::signature::{ED25519, Ed25519KeyPair, KeyPair, ParsedPublicKey, UnparsedPublicKey};
use js::context::JSContext;
use rand::TryRngCore;
use rand::rngs::OsRng;

use crate::dom::bindings::codegen::Bindings::CryptoKeyBinding::{
    CryptoKeyMethods, CryptoKeyPair, KeyType, KeyUsage,
};
use crate::dom::bindings::codegen::Bindings::SubtleCryptoBinding::{JsonWebKey, KeyFormat};
use crate::dom::bindings::error::Error;
use crate::dom::bindings::root::DomRoot;
use crate::dom::bindings::str::DOMString;
use crate::dom::cryptokey::{CryptoKey, Handle};
use crate::dom::globalscope::GlobalScope;
use crate::dom::subtlecrypto::{
    CryptoAlgorithm, ExportedKey, JsonWebKeyExt, JwkStringField, KeyAlgorithmAndDerivatives,
    SubtleKeyAlgorithm,
};

const ED25519_SEED_LENGTH: usize = 32;

/// <https://w3c.github.io/webcrypto/#ed25519-operations-sign>
pub(crate) fn sign(key: &CryptoKey, message: &[u8]) -> Result<Vec<u8>, Error> {
    // Step 1. If the [[type]] internal slot of key is not "private", then throw an
    // InvalidAccessError.
    if key.Type() != KeyType::Private {
        return Err(Error::InvalidAccess(Some(
            "[[type]] internal slot of key is not \"private\"".into(),
        )));
    }

    // Step 2. Let result be the result of performing the Ed25519 signing process, as specified in
    // [RFC8032], Section 5.1.6, with message as M, using the Ed25519 private key associated with
    // key.
    let key_pair =
        Ed25519KeyPair::from_seed_unchecked(key.handle().as_bytes()).map_err(|error| {
            Error::Operation(Some(format!(
                "The key was rejected for the following reason: {error}"
            )))
        })?;
    let result = key_pair.sign(message).as_ref().to_vec();

    // Step 3. Return result.
    Ok(result)
}

/// <https://w3c.github.io/webcrypto/#ed25519-operations-verify>
pub(crate) fn verify(key: &CryptoKey, message: &[u8], signature: &[u8]) -> Result<bool, Error> {
    // Step 1. If the [[type]] internal slot of key is not "public", then throw an
    // InvalidAccessError.
    if key.Type() != KeyType::Public {
        return Err(Error::InvalidAccess(Some(
            "[[type]] internal slot of key is not \"public\"".into(),
        )));
    }

    // Step 2. If the key data of key represents an invalid point or a small-order element on the
    // Elliptic Curve of Ed25519, return false.
    // NOTE: Not all implementations perform this check. See WICG/webcrypto-secure-curves issue 27.

    // Step 3. If the point R, encoded in the first half of signature, represents an invalid point
    // or a small-order element on the Elliptic Curve of Ed25519, return false.
    // NOTE: Not all implementations perform this check. See WICG/webcrypto-secure-curves issue 27.

    // Step 4. Perform the Ed25519 verification steps, as specified in [RFC8032], Section
    // 5.1.7, using the cofactorless (unbatched) equation, [S]B = R + [k]A', on the signature, with
    // message as M, using the Ed25519 public key associated with key.
    // Step 5. Let result be a boolean with the value true if the signature is valid and the value
    // false otherwise.
    let public_key = UnparsedPublicKey::new(&ED25519, key.handle().as_bytes());
    let result = match public_key.verify(message, signature) {
        Ok(()) => true,
        Err(aws_lc_rs::error::Unspecified) => false,
    };

    // Step 6. Return result.
    Ok(result)
}

/// <https://w3c.github.io/webcrypto/#ed25519-operations-generate-key>
pub(crate) fn generate_key(
    cx: &mut JSContext,
    global: &GlobalScope,
    extractable: bool,
    usages: Vec<KeyUsage>,
) -> Result<CryptoKeyPair, Error> {
    // Step 1. If usages contains any entry which is not "sign" or "verify", then throw a
    // SyntaxError.
    if usages
        .iter()
        .any(|usage| !matches!(usage, KeyUsage::Sign | KeyUsage::Verify))
    {
        return Err(Error::Syntax(Some(
            "Usages contains an entry which is not \"sign\" or \"verify\"".into(),
        )));
    }

    // Step 2. Generate an Ed25519 key pair, as defined in [RFC8032], section 5.1.5.
    let mut seed = vec![0u8; ED25519_SEED_LENGTH];
    if OsRng.try_fill_bytes(&mut seed).is_err() {
        return Err(Error::Operation(Some("Error getting random data".into())));
    }
    let key_pair = Ed25519KeyPair::from_seed_unchecked(&seed).map_err(|error| {
        Error::Operation(Some(format!(
            "The key was rejected for the following reason: {error}"
        )))
    })?;

    // Step 3. Let algorithm be a new KeyAlgorithm object.
    // Step 4. Set the name attribute of algorithm to "Ed25519".
    let algorithm = SubtleKeyAlgorithm {
        name: CryptoAlgorithm::Ed25519,
    };

    // Step 5. Let publicKey be a new CryptoKey representing the public key of the generated key pair.
    // Step 6. Set the [[type]] internal slot of publicKey to "public"
    // Step 7. Set the [[algorithm]] internal slot of publicKey to algorithm.
    // Step 8. Set the [[extractable]] internal slot of publicKey to true.
    // Step 9. Set the [[usages]] internal slot of publicKey to be the usage intersection of usages
    // and [ "verify" ].
    let public_key = CryptoKey::new(
        cx,
        global,
        KeyType::Public,
        true,
        KeyAlgorithmAndDerivatives::KeyAlgorithm(algorithm.clone()),
        usages
            .iter()
            .filter(|&usage| *usage == KeyUsage::Verify)
            .cloned()
            .collect(),
        Handle::Ed25519PublicKey(key_pair.public_key().as_ref().to_vec()),
    );

    // Step 10. Let privateKey be a new CryptoKey representing the private key of the generated key pair.
    // Step 11. Set the [[type]] internal slot of privateKey to "private"
    // Step 12. Set the [[algorithm]] internal slot of privateKey to algorithm.
    // Step 13. Set the [[extractable]] internal slot of privateKey to extractable.
    // Step 14. Set the [[usages]] internal slot of privateKey to be the usage intersection of
    // usages and [ "sign" ].
    let private_key = CryptoKey::new(
        cx,
        global,
        KeyType::Private,
        extractable,
        KeyAlgorithmAndDerivatives::KeyAlgorithm(algorithm),
        usages
            .iter()
            .filter(|&usage| *usage == KeyUsage::Sign)
            .cloned()
            .collect(),
        Handle::Ed25519PrivateKey(seed),
    );

    // Step 16. Let result be a new CryptoKeyPair dictionary.
    // Step 17. Set the publicKey attribute of result to be publicKey.
    // Step 18. Set the privateKey attribute of result to be privateKey.
    let result = CryptoKeyPair {
        publicKey: Some(public_key),
        privateKey: Some(private_key),
    };

    // Step 19. Return result.
    Ok(result)
}

/// <https://w3c.github.io/webcrypto/#ed25519-operations-import-key>
pub(crate) fn import_key(
    cx: &mut JSContext,
    global: &GlobalScope,
    format: KeyFormat,
    key_data: &[u8],
    extractable: bool,
    usages: Vec<KeyUsage>,
) -> Result<DomRoot<CryptoKey>, Error> {
    // Step 1. Let keyData be the key data to be imported.
    // NOTE: It is given as a method parameter.

    // Step 2.
    let key = match format {
        // If format is "spki":
        KeyFormat::Spki => {
            // Step 2.1. If usages contains a value which is not "verify" then throw a SyntaxError.
            if usages.iter().any(|usage| *usage != KeyUsage::Verify) {
                return Err(Error::Syntax(Some(
                    "Usages contains an entry which is not \"verify\"".into(),
                )));
            }

            // Step 2.2. Let spki be the result of running the parse a subjectPublicKeyInfo
            // algorithm over keyData.
            // Step 2.3. If an error occurred while parsing, then throw a DataError.
            // Step 2.4. If the algorithm object identifier field of the algorithm
            // AlgorithmIdentifier field of spki is not equal to the id-Ed25519 object identifier
            // defined in [RFC8410], then throw a DataError.
            // Step 2.5. If the parameters field of the algorithm AlgorithmIdentifier field of spki
            // is present, then throw a DataError.
            // Step 2.6. Let publicKey be the Ed25519 public key identified by the subjectPublicKey
            // field of spki.
            let public_key = ParsedPublicKey::new(&ED25519, key_data).map_err(|error| {
                Error::Data(Some(format!(
                    "The key was rejected for the following reason: {error}"
                )))
            })?;

            // Step 2.9. Let algorithm be a new KeyAlgorithm.
            // Step 2.10. Set the name attribute of algorithm to "Ed25519".
            let algorithm = SubtleKeyAlgorithm {
                name: CryptoAlgorithm::Ed25519,
            };

            // Step 2.7. Let key be a new CryptoKey that represents publicKey.
            // Step 2.8. Set the [[type]] internal slot of key to "public"
            // Step 2.11. Set the [[algorithm]] internal slot of key to algorithm.
            CryptoKey::new(
                cx,
                global,
                KeyType::Public,
                extractable,
                KeyAlgorithmAndDerivatives::KeyAlgorithm(algorithm),
                usages,
                Handle::Ed25519PublicKey(public_key.as_ref().to_vec()),
            )
        },
        // If format is "pkcs8":
        KeyFormat::Pkcs8 => {
            // Step 2.1. If usages contains a value which is not "sign" then throw a SyntaxError.
            if usages.iter().any(|usage| *usage != KeyUsage::Sign) {
                return Err(Error::Syntax(Some(
                    "Usages contains an entry which is not \"sign\"".into(),
                )));
            }

            // Step 2.2. Let privateKeyInfo be the result of running the parse a privateKeyInfo
            // algorithm over keyData.
            // Step 2.3. If an error occurs while parsing, then throw a DataError.
            // Step 2.4. If the algorithm object identifier field of the privateKeyAlgorithm
            // PrivateKeyAlgorithm field of privateKeyInfo is not equal to the id-Ed25519 object
            // identifier defined in [RFC8410], then throw a DataError.
            // Step 2.5. If the parameters field of the privateKeyAlgorithm
            // PrivateKeyAlgorithmIdentifier field of privateKeyInfo is present, then throw a
            // DataError.
            let private_key_info = Ed25519KeyPair::from_pkcs8(key_data).map_err(|error| {
                Error::Data(Some(format!(
                    "The key was rejected for the following reason: {error}"
                )))
            })?;

            // Step 2.6. Let curvePrivateKey be the result of performing the parse an ASN.1
            // structure algorithm, with data as the privateKey field of privateKeyInfo, structure
            // as the ASN.1 CurvePrivateKey structure specified in Section 7 of [RFC8410], and
            // exactData set to true.
            // Step 2.7. If an error occurred while parsing, then throw a DataError.
            let curve_private_key = private_key_info
                .seed()
                .map_err(|_| {
                    Error::Data(Some("Failed to get the seed from the private key".into()))
                })?
                .as_be_bytes()
                .map_err(|_| {
                    Error::Data(Some(
                        "Failed to serialize the seed of the private key".into(),
                    ))
                })?
                .as_ref()
                .to_vec();

            // Step 2.10. Let algorithm be a new KeyAlgorithm.
            // Step 2.11. Set the name attribute of algorithm to "Ed25519".
            let algorithm = SubtleKeyAlgorithm {
                name: CryptoAlgorithm::Ed25519,
            };

            // Step 2.8. Let key be a new CryptoKey that represents the Ed25519 private key
            // identified by curvePrivateKey.
            // Step 2.9. Set the [[type]] internal slot of key to "private"
            // Step 2.12. Set the [[algorithm]] internal slot of key to algorithm.
            CryptoKey::new(
                cx,
                global,
                KeyType::Private,
                extractable,
                KeyAlgorithmAndDerivatives::KeyAlgorithm(algorithm),
                usages,
                Handle::Ed25519PrivateKey(curve_private_key),
            )
        },
        // If format is "jwk":
        KeyFormat::Jwk => {
            // Step 2.1. If keyData is a JsonWebKey dictionary: Let jwk equal keyData.
            // Otherwise: Throw a DataError.
            let jwk = JsonWebKey::parse(cx, key_data)?;

            // Step 2.2 If the d field is present and usages contains a value which is not "sign",
            // or, if the d field is not present and usages contains a value which is not "verify"
            // then throw a SyntaxError.
            if jwk.d.as_ref().is_some() && usages.iter().any(|usage| *usage != KeyUsage::Sign) {
                return Err(Error::Syntax(Some(
                    "The 'd' field is present, but there are usages different than 'sign'".into(),
                )));
            }
            if jwk.d.as_ref().is_none() && usages.iter().any(|usage| *usage != KeyUsage::Verify) {
                return Err(Error::Syntax(Some(
                    "The 'd' field is not present, but there are usages different than 'verify'"
                        .into(),
                )));
            }

            // Step 2.3 If the kty field of jwk is not "OKP", then throw a DataError.
            if jwk.kty.as_ref().is_none_or(|kty| kty != "OKP") {
                return Err(Error::Data(Some(
                    "The 'kty' field is different from 'OKP'".into(),
                )));
            }

            // Step 2.4 If the crv field of jwk is not "Ed25519", then throw a DataError.
            if jwk.crv.as_ref().is_none_or(|crv| crv != "Ed25519") {
                return Err(Error::Data(Some(
                    "The 'crv' field of the key is different from 'Ed25519'".into(),
                )));
            }

            // Step 2.5 If the alg field of jwk is present and is not "Ed25519" or "EdDSA", then
            // throw a DataError.
            if jwk
                .alg
                .as_ref()
                .is_some_and(|alg| !matches!(alg.str().as_ref(), "Ed25519" | "EdDSA"))
            {
                return Err(Error::Data(Some(
                    "The 'alg' field is different from 'Ed25519' and 'EdDSA'".into(),
                )));
            }

            // Step 2.6 If usages is non-empty and the use field of jwk is present and is not
            // "sig", then throw a DataError.
            if !usages.is_empty() && jwk.use_.as_ref().is_some_and(|use_| use_ != "sig") {
                return Err(Error::Data(Some(
                    "There are usages, but the 'use' field is different from 'sig'".into(),
                )));
            }

            // Step 2.7 If the key_ops field of jwk is present, and is invalid according to the
            // requirements of JSON Web Key [JWK], or it does not contain all of the specified
            // usages values, then throw a DataError.
            jwk.check_key_ops(&usages)?;

            // Step 2.8 If the ext field of jwk is present and has the value false and extractable
            // is true, then throw a DataError.
            if jwk.ext.as_ref().is_some_and(|ext| !ext) && extractable {
                return Err(Error::Data(Some(
                    "The 'ext' field is false, but 'extractable' is true".into(),
                )));
            }

            // Step 2.10. Let algorithm be a new instance of a KeyAlgorithm object.
            // Step 2.11. Set the name attribute of algorithm to "Ed25519".
            let algorithm = SubtleKeyAlgorithm {
                name: CryptoAlgorithm::Ed25519,
            };

            // Step 2.9
            // If the d field is present:
            if jwk.d.is_some() {
                // Step 2.9.1. If jwk does not meet the requirements of the JWK private key format
                // described in Section 2 of [RFC8037], then throw a DataError.
                let d = jwk.decode_required_string_field(JwkStringField::D)?;
                let x = jwk.decode_required_string_field(JwkStringField::X)?;
                let _ = Ed25519KeyPair::from_seed_and_public_key(&d, &x).map_err(|error| {
                    Error::Data(Some(format!(
                        "Key rejected for the following reason: {error}"
                    )))
                })?;

                // Step 2.9.2. Let key be a new CryptoKey object that represents the Ed25519
                // private key identified by interpreting jwk according to Section
                // 2 of [RFC8037]
                // Step 2.9.3. Set the [[type]] internal slot of Key to "private".
                CryptoKey::new(
                    cx,
                    global,
                    KeyType::Private,
                    extractable,
                    KeyAlgorithmAndDerivatives::KeyAlgorithm(algorithm),
                    usages,
                    Handle::Ed25519PrivateKey(d),
                )
            }
            // Otherwise:
            else {
                // Step 2.9.1. If jwk does not meet the requirements of the JWK public key format
                // described in Section 2 of [RFC8037], then throw a DataError.
                let x = jwk.decode_required_string_field(JwkStringField::X)?;

                // Step 2.9.2. Let key be a new CryptoKey object that represents the Ed25519 public
                // key identified by interpreting jwk according to Section 2 of [RFC8037].
                // Step 2.9.3. Set the [[type]] internal slot of Key to "public".
                CryptoKey::new(
                    cx,
                    global,
                    KeyType::Public,
                    extractable,
                    KeyAlgorithmAndDerivatives::KeyAlgorithm(algorithm),
                    usages,
                    Handle::Ed25519PublicKey(x),
                )
            }

            // Step 2.12. Set the [[algorithm]] internal slot of key to algorithm.
            // NOTE: Done in Step 2.9
        },
        // If format is "raw":
        KeyFormat::Raw | KeyFormat::Raw_public => {
            // Step 2.1. If usages contains a value which is not "verify" then throw a SyntaxError.
            if usages.iter().any(|usage| *usage != KeyUsage::Verify) {
                return Err(Error::Syntax(Some(
                    "Usages contains an entry which is not one of \"verify\"".into(),
                )));
            }

            // Step 2.2. If the length in bits of keyData is not 256 then throw a DataError.
            if key_data.len() * 8 != 256 {
                return Err(Error::Data(Some("The key length is not 256 bits".into())));
            }

            // Step 2.3. Let algorithm be a new KeyAlgorithm object.
            // Step 2.4. Set the name attribute of algorithm to "Ed25519".
            let algorithm = SubtleKeyAlgorithm {
                name: CryptoAlgorithm::Ed25519,
            };

            // Step 2.5. Let key be a new CryptoKey representing the key data provided in keyData.
            // Step 2.6. Set the [[type]] internal slot of key to "public"
            // Step 2.7. Set the [[algorithm]] internal slot of key to algorithm.
            CryptoKey::new(
                cx,
                global,
                KeyType::Public,
                extractable,
                KeyAlgorithmAndDerivatives::KeyAlgorithm(algorithm),
                usages,
                Handle::Ed25519PublicKey(key_data.to_vec()),
            )
        },
        // Otherwise:
        _ => {
            // throw a NotSupportedError.
            return Err(Error::NotSupported(Some(
                "Unsupported import key format for ED25519 key".into(),
            )));
        },
    };

    // Step 3. Return key
    Ok(key)
}

/// Steps 9-15 <https://wicg.github.io/webcrypto-modern-algos/#SubtleCrypto-method-getPublicKey>
pub(crate) fn get_public_key(
    cx: &mut JSContext,
    global: &GlobalScope,
    key: &CryptoKey,
    algorithm: &KeyAlgorithmAndDerivatives,
    usages: Vec<KeyUsage>,
) -> Result<DomRoot<CryptoKey>, Error> {
    // NOTE: Steps 1-8 and 16-18 are handled by `SubtleCrypto::GetPublicKey`.

    // Step 9. If usages contains an entry which is not supported for a public key by the algorithm
    // identified by algorithm, then throw a SyntaxError.
    if usages.iter().any(|usage| *usage != KeyUsage::Verify) {
        return Err(Error::Syntax(Some(
            "Usages contains an entry which is not supported for a public key by the algorithm \
             identified by algorithm"
                .into(),
        )));
    }

    // Step 10. Let publicKey be a new CryptoKey representing the public key corresponding to the
    // private key represented by the [[handle]] internal slot of key.
    let seed = key.handle().as_bytes();
    let key_pair = Ed25519KeyPair::from_seed_unchecked(seed).map_err(|_| {
        // Step 11. If an error occurred, then throw a OperationError.
        Error::Operation(None)
    })?;
    let public_key_bytes = key_pair.public_key().as_ref().to_vec();

    // Step 12. Set the [[type]] internal slot of publicKey to "public".
    // Step 13. Set the [[algorithm]] internal slot of publicKey to algorithm.
    // Step 14. Set the [[extractable]] internal slot of publicKey to true.
    // Step 15. Set the [[usages]] internal slot of publicKey to usages.
    Ok(CryptoKey::new(
        cx,
        global,
        KeyType::Public,
        true,
        algorithm.clone(),
        usages,
        Handle::Ed25519PublicKey(public_key_bytes),
    ))
}

/// <https://w3c.github.io/webcrypto/#ed25519-operations-export-key>
pub(crate) fn export_key(format: KeyFormat, key: &CryptoKey) -> Result<ExportedKey, Error> {
    // Step 1. Let key be the CryptoKey to be exported.
    // NOTE: It is given as a method parameter.

    // Step 2. If the underlying cryptographic key material represented by the [[handle]] internal
    // slot of key cannot be accessed, then throw an OperationError.
    // NOTE: key.handle() guarantees access.
    let key_data = key.handle().as_bytes();

    // Step 3.
    let result = match format {
        // If format is "spki":
        KeyFormat::Spki => {
            // Step 3.1. If the [[type]] internal slot of key is not "public", then throw an
            // InvalidAccessError.
            if key.Type() != KeyType::Public {
                return Err(Error::InvalidAccess(Some(
                    "[[type]] internal slot of key is not \"public\"".into(),
                )));
            }

            // Step 3.2. Let data be an instance of the SubjectPublicKeyInfo ASN.1 structure
            // defined in [RFC5280] with the following properties:
            //     Set the algorithm field to an AlgorithmIdentifier ASN.1 type with the following
            //     properties:
            //         Set the algorithm object identifier to the id-Ed25519 OID defined in
            //         [RFC8410].
            //     Set the subjectPublicKey field to keyData.
            let data = ParsedPublicKey::new(&ED25519, key_data).map_err(|error| {
                Error::Operation(Some(format!(
                    "The key was rejected for the following reason: {error}"
                )))
            })?;

            // Step 3.3. Let result be the result of DER-encoding data.
            ExportedKey::Bytes(
                data.as_der()
                    .map_err(|_| {
                        Error::Operation(Some(
                            "Failed to serialize the key into a DER format".into(),
                        ))
                    })?
                    .as_ref()
                    .to_vec(),
            )
        },
        // If format is "pkcs8":
        KeyFormat::Pkcs8 => {
            // Step 3.1. If the [[type]] internal slot of key is not "private", then throw an
            // InvalidAccessError.
            if key.Type() != KeyType::Private {
                return Err(Error::InvalidAccess(Some(
                    "[[type]] internal slot of key is not \"private\"".into(),
                )));
            }

            // Step 3.2. Let data be an instance of the PrivateKeyInfo ASN.1 structure defined in
            // [RFC5208] with the following properties:
            //     Set the version field to 0.
            //     Set the privateKeyAlgorithm field to a PrivateKeyAlgorithmIdentifier ASN.1 type
            //     with the following properties:
            //         Set the algorithm object identifier to the id-Ed25519 OID defined in
            //         [RFC8410].
            //     Set the privateKey field to the result of DER-encoding a CurvePrivateKey ASN.1
            //     type, as defined in Section 7 of [RFC8410], that represents the Ed25519 private
            //     key represented by the [[handle]] internal slot of key
            let data = Ed25519KeyPair::from_seed_unchecked(key_data)
                .map_err(|error| {
                    Error::Operation(Some(format!(
                        "The key was rejected for the following reason: {error}"
                    )))
                })?
                .to_pkcs8v1()
                .map_err(|_| {
                    Error::Operation(Some(
                        "Failed to serialize the key into a PKCS#8 format".into(),
                    ))
                })?;

            // Step 3.3. Let result be the result of DER-encoding data.
            ExportedKey::Bytes(data.as_ref().to_vec())
        },
        // If format is "jwk":
        KeyFormat::Jwk => {
            // Step 3.1. Let jwk be a new JsonWebKey dictionary.
            // Step 3.2. Set the kty attribute of jwk to "OKP".
            // Step 3.3. Set the alg attribute of jwk to "Ed25519".
            // Step 3.4. Set the crv attribute of jwk to "Ed25519".
            let mut jwk = JsonWebKey {
                kty: Some(DOMString::from("OKP")),
                alg: Some(DOMString::from("Ed25519")),
                crv: Some(DOMString::from("Ed25519")),
                ..Default::default()
            };

            // Step 3.5. Set the x attribute of jwk according to the definition in Section 2 of [RFC8037].
            // Step 3.6.
            // If the [[type]] internal slot of key is "private"
            //     Set the d attribute of jwk according to the definition in Section 2 of [RFC8037].
            match key.Type() {
                KeyType::Public => {
                    jwk.encode_string_field(JwkStringField::X, key_data);
                },
                KeyType::Private => {
                    let key_pair =
                        Ed25519KeyPair::from_seed_unchecked(key_data).map_err(|error| {
                            Error::Data(Some(format!(
                                "The key was rejected for the following reason: {error}"
                            )))
                        })?;
                    jwk.encode_string_field(JwkStringField::X, key_pair.public_key().as_ref());
                    jwk.encode_string_field(JwkStringField::D, key_data);
                },
                KeyType::Secret => {
                    return Err(Error::Data(Some("Cannot export a secret key".into())));
                },
            }

            // Step 3.7. Set the key_ops attribute of jwk to the usages attribute of key.
            jwk.set_key_ops(key.usages());

            // Step 3.8. Set the ext attribute of jwk to the [[extractable]] internal slot of key.
            jwk.ext = Some(key.Extractable());

            // Step 3.9. Let result be jwk.
            ExportedKey::Jwk(Box::new(jwk))
        },
        // If format is "raw":
        KeyFormat::Raw | KeyFormat::Raw_public => {
            // Step 3.1. If the [[type]] internal slot of key is not "public", then throw an
            // InvalidAccessError.
            if key.Type() != KeyType::Public {
                return Err(Error::InvalidAccess(Some(
                    "[[type]] internal slot of key is not \"public\"".into(),
                )));
            }

            // Step 3.2. Let data be a byte sequence representing the Ed25519 public key
            // represented by the [[handle]] internal slot of key.
            // Step 3.3. Let result be data.
            ExportedKey::Bytes(key_data.to_vec())
        },
        // Otherwise:
        _ => {
            // throw a NotSupportedError.
            return Err(Error::NotSupported(Some(
                "Unsupported export key format for ED25519 key".into(),
            )));
        },
    };

    // Step 4. Return result.
    Ok(result)
}