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//===----------------------------------------------------------------------===//
//
// This source file is part of the SwiftCrypto open source project
//
// Copyright (c) 2019-2020 Apple Inc. and the SwiftCrypto project authors
// Licensed under Apache License v2.0
//
// See LICENSE.txt for license information
// See CONTRIBUTORS.md for the list of SwiftCrypto project authors
//
// SPDX-License-Identifier: Apache-2.0
//
//===----------------------------------------------------------------------===//
#if CRYPTO_IN_SWIFTPM && !CRYPTO_IN_SWIFTPM_FORCE_BUILD_API
@_exported import CryptoKit
#else
import Foundation
/// A hash-based message authentication algorithm.
///
/// Use hash-based message authentication to create a code with a value that’s
/// dependent on both a block of data and a symmetric cryptographic key. Another
/// party with access to the data and the same secret key can compute the code
/// again and compare it to the original to detect whether the data changed.
/// This serves a purpose similar to digital signing and verification, but
/// depends on a shared symmetric key instead of public-key cryptography.
///
/// As with digital signing, the data isn’t hidden by this process. When you
/// need to encrypt the data as well as authenticate it, use a cipher like
/// ``AES`` or ``ChaChaPoly`` to put the data into a sealed box (an instance of
/// ``AES/GCM/SealedBox`` or ``ChaChaPoly/SealedBox``).
public struct HMAC<H: HashFunction>: MACAlgorithm {
/// An alias for the symmetric key type used to compute or verify a message
/// authentication code.
public typealias Key = SymmetricKey
/// An alias for a hash-based message authentication code.
public typealias MAC = HashedAuthenticationCode<H>
var outerHasher: H
var innerHasher: H
/// Returns a Boolean value indicating whether the given message
/// authentication code is valid for a block of data stored in a buffer.
///
/// - Parameters:
/// - mac: The authentication code to compare.
/// - bufferPointer: A pointer to the block of data to compare.
/// - key: The symmetric key for the authentication code.
///
/// - Returns: A Boolean value that’s `true` if the message authentication
/// code is valid for the data within the specified buffer.
public static func isValidAuthenticationCode(_ mac: MAC, authenticating bufferPointer: UnsafeRawBufferPointer, using key: SymmetricKey) -> Bool {
return isValidAuthenticationCode(authenticationCodeBytes: mac, authenticatedData: bufferPointer, key: key)
}
/// Creates a message authentication code generator.
///
/// - Parameters:
/// - key: The symmetric key used to secure the computation.
public init(key: SymmetricKey) {
#if os(iOS) && (arch(arm) || arch(i386))
fatalError("Unsupported architecture")
#else
var K: ContiguousBytes
if key.byteCount == H.blockByteCount {
K = key
} else if key.byteCount > H.blockByteCount {
var array = Array(repeating: UInt8(0), count: H.blockByteCount)
K = key.withUnsafeBytes { (keyBytes) in
let hash = H.hash(bufferPointer: keyBytes)
return hash.withUnsafeBytes({ (hashBytes) in
memcpy(&array, hashBytes.baseAddress!, hashBytes.count)
return array
})
}
} else {
var keyArray = Array(repeating: UInt8(0), count: H.blockByteCount)
key.withUnsafeBytes { keyArray.replaceSubrange(0..<$0.count, with: $0) }
K = keyArray
}
self.innerHasher = H()
let innerKey = K.withUnsafeBytes {
return $0.map({ (keyByte) in
keyByte ^ 0x36
})
}
innerHasher.update(data: innerKey)
self.outerHasher = H()
let outerKey = K.withUnsafeBytes {
return $0.map({ (keyByte) in
keyByte ^ 0x5c
})
}
outerHasher.update(data: outerKey)
#endif
}
/// Computes a message authentication code for the given data.
///
/// - Parameters:
/// - data: The data for which to compute the authentication code.
/// - key: The symmetric key used to secure the computation.
///
/// - Returns: The message authentication code.
public static func authenticationCode<D: DataProtocol>(for data: D, using key: SymmetricKey) -> MAC {
var authenticator = Self(key: key)
authenticator.update(data: data)
return authenticator.finalize()
}
/// Returns a Boolean value indicating whether the given message
/// authentication code is valid for a block of data.
///
/// - Parameters:
/// - authenticationCode: The authentication code to compare.
/// - authenticatedData: The block of data to compare.
/// - key: The symmetric key for the authentication code.
///
/// - Returns: A Boolean value that’s `true` if the message authentication
/// code is valid for the specified block of data.
public static func isValidAuthenticationCode<D: DataProtocol>(_ authenticationCode: MAC, authenticating authenticatedData: D, using key: SymmetricKey) -> Bool {
return isValidAuthenticationCode(authenticationCodeBytes: authenticationCode, authenticatedData: authenticatedData, key: key)
}
/// Returns a Boolean value indicating whether the given message
/// authentication code represented as contiguous bytes is valid for a block
/// of data.
///
/// - Parameters:
/// - authenticationCode: The authentication code to compare.
/// - authenticatedData: The block of data to compare.
/// - key: The symmetric key for the authentication code.
///
/// - Returns: A Boolean value that’s `true` if the message authentication
/// code is valid for the specified block of data.
public static func isValidAuthenticationCode<C: ContiguousBytes, D: DataProtocol>(_ authenticationCode: C,
authenticating authenticatedData: D,
using key: SymmetricKey) -> Bool {
return isValidAuthenticationCode(authenticationCodeBytes: authenticationCode, authenticatedData: authenticatedData, key: key)
}
/// Updates the message authentication code computation with a block of
/// data.
///
/// - Parameters:
/// - data: The data for which to compute the authentication code.
public mutating func update<D: DataProtocol>(data: D) {
data.regions.forEach { (memoryRegion) in
memoryRegion.withUnsafeBytes({ (bp) in
self.update(bufferPointer: bp)
})
}
}
/// Finalizes the message authentication computation and returns the
/// computed code.
///
/// - Returns: The message authentication code.
public func finalize() -> MAC {
let innerHash = innerHasher.finalize()
var outerHashForFinalization = outerHasher
let mac = innerHash.withUnsafeBytes { buffer -> H.Digest in
outerHashForFinalization.update(bufferPointer: (buffer))
return outerHashForFinalization.finalize()
}
return HashedAuthenticationCode(digest: mac)
}
/// Adds data to be authenticated by MAC function. This can be called one or more times to append additional data.
///
/// - Parameters:
/// - data: The data to be authenticated.
/// - Throws: Throws if the HMAC has already been finalized.
mutating func update(bufferPointer: UnsafeRawBufferPointer) {
innerHasher.update(bufferPointer: bufferPointer)
}
/// A common implementation of isValidAuthenticationCode shared by the various entry points.
private static func isValidAuthenticationCode<C: ContiguousBytes, D: DataProtocol>(authenticationCodeBytes: C,
authenticatedData: D,
key: SymmetricKey) -> Bool {
var authenticator = Self(key: key)
authenticator.update(data: authenticatedData)
let computedMac = authenticator.finalize()
return safeCompare(authenticationCodeBytes, computedMac)
}
}
/// A hash-based message authentication code.
public struct HashedAuthenticationCode<H: HashFunction>: MessageAuthenticationCode {
let digest: H.Digest
/// The number of bytes in the message authentication code.
public var byteCount: Int {
return H.Digest.byteCount
}
/// A human-readable description of the code.
public var description: String {
return "HMAC with \(H.self): \(Array(digest).hexString)"
}
/// Invokes the given closure with a buffer pointer covering the raw bytes
/// of the code.
///
/// - Parameters:
/// - body: A closure that takes a raw buffer pointer to the bytes of the
/// code and returns the code.
///
/// - Returns: The code, as returned from the body closure.
public func withUnsafeBytes<R>(_ body: (UnsafeRawBufferPointer) throws -> R) rethrows -> R {
return try digest.withUnsafeBytes(body)
}
}
#endif // Linux or !SwiftPM
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