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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift open source project
//
// Copyright (c) 2021-2023 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//===----------------------------------------------------------------------===//
//
// This source file is part of the Vapor open source project
//
// Copyright (c) 2017-2020 Vapor project authors
// Licensed under MIT
//
// See LICENSE for license information
//
// SPDX-License-Identifier: MIT
//
//===----------------------------------------------------------------------===//
import Foundation
#if USE_IMPL_ONLY_IMPORTS
@_implementationOnly import _CryptoExtras
@_implementationOnly import Crypto
@_implementationOnly import X509
#else
import _CryptoExtras
import Crypto
import X509
#endif
// The logic in this source file loosely follows https://www.rfc-editor.org/rfc/rfc7515.html
// for JSON Web Signature (JWS).
struct Signature {
let header: Header
let payload: Data
let signature: Data
}
extension Signature {
enum Algorithm: String, Codable {
case RS256 // RSASSA-PKCS1-v1_5 using SHA-256
case ES256 // ECDSA using P-256 and SHA-256
}
struct Header: Equatable, Codable {
// https://www.rfc-editor.org/rfc/rfc7515.html#section-4.1.1
let algorithm: Algorithm
/// Base64 encoded certificate chain
let certChain: [String]
enum CodingKeys: String, CodingKey {
case algorithm = "alg"
case certChain = "x5c"
}
}
}
// Reference: https://github.com/vapor/jwt-kit/blob/master/Sources/JWTKit/JWTSerializer.swift
extension Signature {
static let rsaSigningPadding = _RSA.Signing.Padding.insecurePKCS1v1_5
static func generate(
payload: some Encodable,
certChainData: [Data],
jsonEncoder: JSONEncoder,
signatureAlgorithm: Signature.Algorithm,
signatureProvider: @escaping (Data) throws -> Data
) throws -> Data {
let header = Signature.Header(
algorithm: signatureAlgorithm,
certChain: certChainData.map { $0.base64EncodedString() }
)
let headerData = try jsonEncoder.encode(header)
let encodedHeader = headerData.base64URLEncodedBytes()
let payloadData = try jsonEncoder.encode(payload)
let encodedPayload = payloadData.base64URLEncodedBytes()
// https://www.rfc-editor.org/rfc/rfc7515.html#section-5.1
// Signing input: BASE64URL(header) + '.' + BASE64URL(payload)
let signatureData = try signatureProvider(encodedHeader + .period + encodedPayload)
let encodedSignature = signatureData.base64URLEncodedBytes()
// Result: header.payload.signature
let bytes = encodedHeader
+ .period
+ encodedPayload
+ .period
+ encodedSignature
return bytes
}
}
// Reference: https://github.com/vapor/jwt-kit/blob/master/Sources/JWTKit/JWTParser.swift
extension Signature {
typealias CertChainValidate = ([Data]) async throws -> [Certificate]
static func parse(
_ signature: String,
certChainValidate: CertChainValidate,
jsonDecoder: JSONDecoder
) async throws -> Signature {
let bytes = Array(signature.utf8)
return try await Self.parse(bytes, certChainValidate: certChainValidate, jsonDecoder: jsonDecoder)
}
static func parse(
_ signature: some DataProtocol,
certChainValidate: CertChainValidate,
jsonDecoder: JSONDecoder
) async throws -> Signature {
let parts = signature.copyBytes().split(separator: .period)
guard parts.count == 3 else {
throw SignatureError.malformedSignature
}
let encodedHeader = parts[0]
let encodedPayload = parts[1]
let encodedSignature = parts[2]
guard let headerBytes = encodedHeader.base64URLDecodedBytes(),
let header = try? jsonDecoder.decode(Header.self, from: headerBytes)
else {
throw SignatureError.malformedSignature
}
// Signature header contains the certificate and public key for verification
let certChainData = header.certChain.compactMap { Data(base64Encoded: $0) }
// Make sure we restore all certs successfully
guard certChainData.count == header.certChain.count else {
throw SignatureError.malformedSignature
}
let certChain = try await certChainValidate(certChainData)
guard let payloadBytes = encodedPayload.base64URLDecodedBytes(),
let signatureBytes = encodedSignature.base64URLDecodedBytes()
else {
throw SignatureError.malformedSignature
}
// Extract public key from the certificate
let certificate = certChain.first! // !-safe because certChain is not empty at this point
// Verify the key was used to generate the signature
let message = Data(encodedHeader) + .period + Data(encodedPayload)
let digest = SHA256.hash(data: message)
switch header.algorithm {
case .ES256:
guard let publicKey = P256.Signing.PublicKey(certificate.publicKey) else {
throw SignatureError.invalidPublicKey
}
guard try publicKey.isValidSignature(.init(rawRepresentation: signatureBytes), for: digest)
else {
throw SignatureError.invalidSignature
}
case .RS256:
guard let publicKey = _RSA.Signing.PublicKey(certificate.publicKey) else {
throw SignatureError.invalidPublicKey
}
guard publicKey.isValidSignature(
.init(rawRepresentation: signatureBytes),
for: digest,
padding: .insecurePKCS1v1_5
) else {
throw SignatureError.invalidSignature
}
}
return Signature(header: header, payload: payloadBytes, signature: signatureBytes)
}
}
enum SignatureError: Error {
case malformedSignature
case invalidSignature
case invalidPublicKey
}
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