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Add PEM/DER APIs for Curve25519 (#419)
Add PEM/DER APIs for Curve25519 ### Checklist - [x] I've run tests to see all new and existing tests pass - [x] I've followed the code style of the rest of the project - [x] I've read the [Contribution Guidelines](CONTRIBUTING.md) - [x] I've updated the documentation if necessary #### If you've made changes to `gyb` files - [ ] I've run `./scripts/generate_boilerplate_files_with_gyb.sh` and included updated generated files in a commit of this pull request ### Motivation: Closes #82 Creating Ed25519/X25519 keys using PEM/DER and also generating their PEM/DER representations can be handy ### Modifications: Added - `init(pemRepresentation:)` and the `pemRepresentation` computed property - `init(derRepresentation:)` and the `derRepresentation` computed property to `Curve25519.{Signing,KeyAgreement}.{Private,Public}Key` ### Result: Curve25519 can now be created with and can produce PEM/DER representations
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‎Sources/CryptoExtras/CMakeLists.txt‎

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@@ -33,6 +33,7 @@ add_library(CryptoExtras
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"ARC/ARCServer.swift"
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"ChaCha20CTR/BoringSSL/ChaCha20CTR_boring.swift"
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"ChaCha20CTR/ChaCha20CTR.swift"
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"EC/Curve25519+PEM.swift"
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"EC/ObjectIdentifier.swift"
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"EC/PKCS8DERRepresentation.swift"
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"EC/PKCS8PrivateKey.swift"

‎Sources/CryptoExtras/EC/Curve25519+PEM.swift‎

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//===----------------------------------------------------------------------===//
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//
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// This source file is part of the SwiftCrypto open source project
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//
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// Copyright (c) 2025 Apple Inc. and the SwiftCrypto project authors
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// Licensed under Apache License v2.0
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//
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// See LICENSE.txt for license information
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// See CONTRIBUTORS.txt for the list of SwiftCrypto project authors
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//
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// SPDX-License-Identifier: Apache-2.0
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//
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//===----------------------------------------------------------------------===//
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import Crypto
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import Foundation
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import SwiftASN1
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@available(iOS 14.0, macOS 11.0, watchOS 7.0, tvOS 14.0, *)
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extension Curve25519.Signing.PrivateKey {
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/// A Distinguished Encoding Rules (DER) encoded representation of the private key.
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public var derRepresentation: Data {
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let pkey = ASN1.PKCS8PrivateKey(algorithm: .ed25519, privateKey: Array(self.rawRepresentation))
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var serializer = DER.Serializer()
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try! serializer.serialize(pkey)
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return Data(serializer.serializedBytes)
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}
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/// A Privacy-Enhanced Mail (PEM) representation of the private key.
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public var pemRepresentation: String {
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let pemDocument = ASN1.PEMDocument(type: "PRIVATE KEY", derBytes: self.derRepresentation)
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return pemDocument.pemString
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}
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/// Creates a Curve25519 private key for signing from a Privacy-Enhanced Mail
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/// (PEM) representation.
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///
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/// - Parameters:
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/// - pemRepresentation: A PEM representation of the key.
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public init(pemRepresentation: String) throws {
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let document = try ASN1.PEMDocument(pemString: pemRepresentation)
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self = try .init(derRepresentation: document.derBytes)
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}
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/// Creates a Curve25519 private key for signing from a Distinguished Encoding
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/// Rules (DER) encoded representation.
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///
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/// - Parameters:
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/// - derRepresentation: A DER-encoded representation of the key.
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public init<Bytes: RandomAccessCollection>(derRepresentation: Bytes) throws where Bytes.Element == UInt8 {
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let bytes = Array(derRepresentation)
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let key = try ASN1.PKCS8PrivateKey(derEncoded: bytes)
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self = try .init(rawRepresentation: key.privateKey.bytes)
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}
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}
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@available(iOS 14.0, macOS 11.0, watchOS 7.0, tvOS 14.0, *)
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extension Curve25519.Signing.PublicKey {
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/// A Distinguished Encoding Rules (DER) encoded representation of the public key.
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public var derRepresentation: Data {
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let spki = SubjectPublicKeyInfo(algorithmIdentifier: .ed25519, key: Array(self.rawRepresentation))
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var serializer = DER.Serializer()
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try! serializer.serialize(spki)
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return Data(serializer.serializedBytes)
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}
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/// A Privacy-Enhanced Mail (PEM) representation of the public key.
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public var pemRepresentation: String {
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let pemDocument = ASN1.PEMDocument(type: "PUBLIC KEY", derBytes: self.derRepresentation)
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return pemDocument.pemString
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}
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/// Creates a Curve25519 public key for signing from a Privacy-Enhanced Mail
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/// (PEM) representation.
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///
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/// - Parameters:
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/// - pemRepresentation: A PEM representation of the key.
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public init(pemRepresentation: String) throws {
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let document = try ASN1.PEMDocument(pemString: pemRepresentation)
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self = try .init(derRepresentation: document.derBytes)
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}
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/// Creates a Curve25519 public key for signing from a Distinguished Encoding
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/// Rules (DER) encoded representation.
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///
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/// - Parameters:
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/// - derRepresentation: A DER-encoded representation of the key.
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public init<Bytes: RandomAccessCollection>(derRepresentation: Bytes) throws where Bytes.Element == UInt8 {
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let bytes = Array(derRepresentation)
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let spki = try SubjectPublicKeyInfo(derEncoded: bytes)
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guard spki.algorithmIdentifier == .ed25519 else {
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throw CryptoKitASN1Error.invalidASN1Object
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}
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self = try .init(rawRepresentation: spki.key.bytes)
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}
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}
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@available(iOS 14.0, macOS 11.0, watchOS 7.0, tvOS 14.0, *)
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extension Curve25519.KeyAgreement.PrivateKey {
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/// A Distinguished Encoding Rules (DER) encoded representation of the private key.
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public var derRepresentation: Data {
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let pkey = ASN1.PKCS8PrivateKey(algorithm: .x25519, privateKey: Array(self.rawRepresentation))
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var serializer = DER.Serializer()
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// Serializing this key can't throw
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try! serializer.serialize(pkey)
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return Data(serializer.serializedBytes)
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}
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/// A Privacy-Enhanced Mail (PEM) representation of the private key.
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public var pemRepresentation: String {
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let pemDocument = ASN1.PEMDocument(type: "PRIVATE KEY", derBytes: self.derRepresentation)
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return pemDocument.pemString
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}
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/// Creates a Curve25519 private key for key agreement from a Privacy-Enhanced Mail
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/// (PEM) representation.
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///
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/// - Parameters:
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/// - pemRepresentation: A PEM representation of the key.
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public init(pemRepresentation: String) throws {
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let document = try ASN1.PEMDocument(pemString: pemRepresentation)
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self = try .init(derRepresentation: document.derBytes)
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}
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/// Creates a Curve25519 private key for key agreement from a Distinguished Encoding
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/// Rules (DER) encoded representation.
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///
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/// - Parameters:
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/// - derRepresentation: A DER-encoded representation of the key.
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public init<Bytes: RandomAccessCollection>(derRepresentation: Bytes) throws where Bytes.Element == UInt8 {
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let bytes = Array(derRepresentation)
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let key = try ASN1.PKCS8PrivateKey(derEncoded: bytes)
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self = try .init(rawRepresentation: key.privateKey.bytes)
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}
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}
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@available(iOS 14.0, macOS 11.0, watchOS 7.0, tvOS 14.0, *)
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extension Curve25519.KeyAgreement.PublicKey {
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/// A Distinguished Encoding Rules (DER) encoded representation of the public key.
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public var derRepresentation: Data {
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let spki = SubjectPublicKeyInfo(algorithmIdentifier: .x25519, key: Array(self.rawRepresentation))
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var serializer = DER.Serializer()
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try! serializer.serialize(spki)
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return Data(serializer.serializedBytes)
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}
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/// A Privacy-Enhanced Mail (PEM) representation of the public key.
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public var pemRepresentation: String {
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let pemDocument = ASN1.PEMDocument(type: "PUBLIC KEY", derBytes: self.derRepresentation)
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return pemDocument.pemString
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}
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/// Creates a Curve25519 public key for key agreement from a Privacy-Enhanced Mail
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/// (PEM) representation.
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///
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/// - Parameters:
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/// - pemRepresentation: A PEM representation of the key.
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public init(pemRepresentation: String) throws {
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let document = try ASN1.PEMDocument(pemString: pemRepresentation)
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self = try .init(derRepresentation: document.derBytes)
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}
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/// Creates a Curve25519 public key for key agreement from a Distinguished Encoding
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/// Rules (DER) encoded representation.
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///
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/// - Parameters:
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/// - derRepresentation: A DER-encoded representation of the key.
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public init<Bytes: RandomAccessCollection>(derRepresentation: Bytes) throws where Bytes.Element == UInt8 {
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let bytes = Array(derRepresentation)
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let spki = try SubjectPublicKeyInfo(derEncoded: bytes)
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guard spki.algorithmIdentifier == .x25519 else {
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throw CryptoKitASN1Error.invalidASN1Object
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}
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self = try .init(rawRepresentation: spki.key.bytes)
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}
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}

‎Sources/CryptoExtras/EC/PKCS8DERRepresentation.swift‎

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@@ -20,25 +20,15 @@ import SwiftASN1
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extension Curve25519.Signing.PrivateKey {
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/// A Distinguished Encoding Rules (DER) encoded representation of the private key in PKCS#8 format.
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public var pkcs8DERRepresentation: Data {
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let pkey = ASN1.PKCS8PrivateKey(algorithm: .ed25519, privateKey: Array(self.rawRepresentation))
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var serializer = DER.Serializer()
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// Serializing this key can't throw
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try! serializer.serialize(pkey)
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return Data(serializer.serializedBytes)
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self.derRepresentation
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}
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}
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@available(iOS 14.0, macOS 11.0, watchOS 7.0, tvOS 14.0, *)
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extension Curve25519.KeyAgreement.PrivateKey {
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/// A Distinguished Encoding Rules (DER) encoded representation of the private key in PKCS#8 format.
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public var pkcs8DERRepresentation: Data {
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let pkey = ASN1.PKCS8PrivateKey(algorithm: .x25519, privateKey: Array(self.rawRepresentation))
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var serializer = DER.Serializer()
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// Serializing this key can't throw
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try! serializer.serialize(pkey)
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return Data(serializer.serializedBytes)
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self.derRepresentation
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}
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}
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‎Sources/CryptoExtras/Util/SubjectPublicKeyInfo.swift‎

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return serializer.serializedBytes
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}
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}
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@available(macOS 10.15, iOS 13, watchOS 6, tvOS 13, macCatalyst 13, visionOS 1.0, *)
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extension RFC5480AlgorithmIdentifier {
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static let ed25519 = RFC5480AlgorithmIdentifier(algorithm: .AlgorithmIdentifier.idEd25519, parameters: nil)
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static let x25519 = RFC5480AlgorithmIdentifier(algorithm: .AlgorithmIdentifier.idX25519, parameters: nil)
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}

‎Tests/CryptoExtrasTests/Curve25519DERTests.swift‎

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//===----------------------------------------------------------------------===//
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//
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// This source file is part of the SwiftCrypto open source project
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//
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// Copyright (c) 2025 Apple Inc. and the SwiftCrypto project authors
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// Licensed under Apache License v2.0
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//
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// See LICENSE.txt for license information
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// See CONTRIBUTORS.txt for the list of SwiftCrypto project authors
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//
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// SPDX-License-Identifier: Apache-2.0
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//
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//===----------------------------------------------------------------------===//
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import CryptoExtras
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import XCTest
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final class Curve25519DERTests: XCTestCase {
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func testSigningPrivateKeyDERRoundTrip() throws {
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let privateKey = Curve25519.Signing.PrivateKey()
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let der = privateKey.derRepresentation
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let imported = try Curve25519.Signing.PrivateKey(derRepresentation: der)
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XCTAssertEqual(imported.rawRepresentation, privateKey.rawRepresentation)
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}
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func testSigningPublicKeyDERRoundTrip() throws {
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let privateKey = Curve25519.Signing.PrivateKey()
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let publicKey = privateKey.publicKey
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let der = publicKey.derRepresentation
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let imported = try Curve25519.Signing.PublicKey(derRepresentation: der)
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XCTAssertEqual(imported.rawRepresentation, publicKey.rawRepresentation)
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}
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func testKeyAgreementPrivateKeyDERRoundTrip() throws {
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let privateKey = Curve25519.KeyAgreement.PrivateKey()
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let der = privateKey.derRepresentation
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let imported = try Curve25519.KeyAgreement.PrivateKey(derRepresentation: der)
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XCTAssertEqual(imported.rawRepresentation, privateKey.rawRepresentation)
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}
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func testKeyAgreementPublicKeyDERRoundTrip() throws {
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let privateKey = Curve25519.KeyAgreement.PrivateKey()
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let publicKey = privateKey.publicKey
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let der = publicKey.derRepresentation
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let imported = try Curve25519.KeyAgreement.PublicKey(derRepresentation: der)
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XCTAssertEqual(imported.rawRepresentation, publicKey.rawRepresentation)
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}
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func testInvalidDERThrows() throws {
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let invalidDER: [UInt8] = [0x01, 0x02, 0x03]
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XCTAssertThrowsError(try Curve25519.Signing.PrivateKey(derRepresentation: invalidDER))
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XCTAssertThrowsError(try Curve25519.Signing.PublicKey(derRepresentation: invalidDER))
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XCTAssertThrowsError(try Curve25519.KeyAgreement.PrivateKey(derRepresentation: invalidDER))
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XCTAssertThrowsError(try Curve25519.KeyAgreement.PublicKey(derRepresentation: invalidDER))
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}
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func testImportOpenSSLSigningPrivateKeyDER() throws {
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// DER extracted from an OpenSSL-generated Ed25519 PKCS#8 PEM
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let derBytes: [UInt8] = [
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0x30, 0x2e, 0x02, 0x01, 0x00, 0x30, 0x05, 0x06, 0x03, 0x2b, 0x65, 0x70,
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0x04, 0x22, 0x04, 0x20, 0x3f, 0x10, 0x52, 0x03, 0xb4, 0x06, 0x87, 0x0c,
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0x51, 0x71, 0xfa, 0xdc, 0x8f, 0x96, 0xbd, 0x2a, 0x5f, 0x42, 0xac, 0x5c,
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0xb9, 0x5b, 0x27, 0x4e, 0xf0, 0x06, 0xe5, 0x61, 0x6a, 0x12, 0x00, 0xa5,
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]
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let key = try Curve25519.Signing.PrivateKey(derRepresentation: derBytes)
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XCTAssertEqual(key.rawRepresentation.count, 32)
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}
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func testImportOpenSSLKeyAgreementPrivateKeyDER() throws {
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// DER extracted from an OpenSSL-generated X25519 PKCS#8 PEM
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let derBytes: [UInt8] = [
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0x30, 0x2e, 0x02, 0x01, 0x00, 0x30, 0x05, 0x06, 0x03, 0x2b, 0x65, 0x6e,
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0x04, 0x22, 0x04, 0x20, 0xb8, 0x38, 0x3f, 0x28, 0xea, 0x8f, 0x1d, 0x71,
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0x49, 0xa2, 0xa3, 0x91, 0x37, 0x00, 0xa1, 0x0c, 0x7c, 0x9d, 0xa9, 0x59,
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0x28, 0x2d, 0x14, 0x7e, 0x9b, 0x1e, 0x1b, 0x8c, 0x04, 0xa5, 0xd8, 0x47,
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]
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let key = try Curve25519.KeyAgreement.PrivateKey(derRepresentation: derBytes)
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XCTAssertEqual(key.rawRepresentation.count, 32)
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}
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}

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