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+//
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+// CryptoSwift
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+//
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+// Copyright (C) 2014-2017 Marcin Krzyżanowski <marcin@krzyzanowskim.com>
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+// This software is provided 'as-is', without any express or implied warranty.
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+//
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+// In no event will the authors be held liable for any damages arising from the use of this software.
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+//
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+// Permission is granted to anyone to use this software for any purpose,including commercial applications, and to alter it and redistribute it freely, subject to the following restrictions:
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+//
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+// - The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation is required.
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+// - Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
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+// - This notice may not be removed or altered from any source or binary distribution.
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+//
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+
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+public class CBCMAC: Authenticator {
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+ public enum Error: Swift.Error {
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+ case wrongKeyLength
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+ }
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+
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+ private let key: SecureBytes
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+
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+ private static let BlockSize: Int = 16
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+ private static let Zero: Array<UInt8> = [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00]
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+ private static let Rb: Array<UInt8> = [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x87]
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+
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+ public init(key: Array<UInt8>) throws {
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+ if key.count != 16 {
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+ throw Error.wrongKeyLength
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+ }
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+ self.key = SecureBytes(bytes: key)
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+ }
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+
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+ // MARK: Authenticator
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+
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+ public func authenticate(_ bytes: Array<UInt8>) throws -> Array<UInt8> {
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+ let aes = try AES(key: Array(key), blockMode: CBC(iv: CBCMAC.Zero), padding: .noPadding)
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+
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+ let l = try aes.encrypt(CBCMAC.Zero)
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+ var subKey1 = leftShiftOneBit(l)
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+ if (l[0] & 0x80) != 0 {
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+ subKey1 = xor(CBCMAC.Rb, subKey1)
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+ }
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+ var subKey2 = leftShiftOneBit(subKey1)
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+ if (subKey1[0] & 0x80) != 0 {
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+ subKey2 = xor(CBCMAC.Rb, subKey2)
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+ }
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+
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+ let lastBlockComplete: Bool
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+ let blockCount = (bytes.count + CBCMAC.BlockSize - 1) / CBCMAC.BlockSize
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+ if blockCount == 0 {
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+ lastBlockComplete = false
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+ } else {
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+ lastBlockComplete = bytes.count % CBCMAC.BlockSize == 0
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+ }
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+ var paddedBytes = bytes
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+ if !lastBlockComplete {
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+ bitPadding(to: &paddedBytes, blockSize: CBCMAC.BlockSize)
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+ }
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+
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+ var blocks = Array(paddedBytes.batched(by: CBCMAC.BlockSize))
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+ var lastBlock = blocks.popLast()!
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+ if lastBlockComplete {
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+ lastBlock = xor(lastBlock, subKey1)
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+ } else {
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+ lastBlock = xor(lastBlock, subKey2)
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+ }
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+
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+ var x = Array<UInt8>(repeating: 0x00, count: CBCMAC.BlockSize)
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+ var y = Array<UInt8>(repeating: 0x00, count: CBCMAC.BlockSize)
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+ for block in blocks {
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+ y = xor(block, x)
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+ x = try aes.encrypt(y)
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+ }
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+ // the difference between CMAC and CBC-MAC is that CMAC xors the final block with a secret value
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+ y = process(lastBlock: lastBlock, with: x)
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+ return try aes.encrypt(y)
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+ }
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+
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+ func process(lastBlock: ArraySlice<UInt8>, with x: [UInt8]) -> [UInt8] {
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+ return Array(lastBlock)
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+ }
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+
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+ // MARK: Helper methods
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+
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+ /**
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+ Performs left shift by one bit to the bit string aquired after concatenating al bytes in the byte array
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+ - parameters:
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+ - bytes: byte array
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+ - returns: bit shifted bit string split again in array of bytes
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+ */
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+ private func leftShiftOneBit(_ bytes: Array<UInt8>) -> Array<UInt8> {
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+ var shifted = Array<UInt8>(repeating: 0x00, count: bytes.count)
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+ let last = bytes.count - 1
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+ for index in 0..<last {
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+ shifted[index] = bytes[index] << 1
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+ if (bytes[index + 1] & 0x80) != 0 {
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+ shifted[index] += 0x01
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+ }
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+ }
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+ shifted[last] = bytes[last] << 1
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+ return shifted
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+ }
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+}
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Marcin Krzyzanowski