CMac constructor

CMac(
  1. BlockCipher cipher,
  2. int macSizeInBits
)

create a standard MAC based on a block cipher with the size of the MAC been given in bits.

Note: the size of the MAC must be at least 24 bits (FIPS Publication 81), or 16 bits if being used as a data authenticator (FIPS Publication 113), and in general should be less than the size of the block cipher as it reduces the chance of an exhaustive attack (see Handbook of Applied Cryptography).

@param cipher the cipher to be used as the basis of the MAC generation. @param macSizeInBits the size of the MAC in bits, must be a multiple of 8 and <= 128.

Implementation

CMac(BlockCipher cipher, int macSizeInBits)
    : _macSize = macSizeInBits ~/ 8,
      _cipher = CBCBlockCipher(cipher) {
  if ((macSizeInBits % 8) != 0) {
    throw ArgumentError('MAC size must be multiple of 8');
  }

  if (macSizeInBits > (_cipher.blockSize * 8)) {
    throw ArgumentError(
        'MAC size must be less or equal to ${_cipher.blockSize * 8}');
  }

  _poly = lookupPoly(cipher.blockSize);

  _mac = Uint8List(cipher.blockSize);

  _buf = Uint8List(cipher.blockSize);

  _zeros = Uint8List(cipher.blockSize);

  _bufOff = 0;
}