/// <summary>
/// Initializes a new instance of the <see cref="AesPmac"/> class with the specified key.
/// </summary>
/// <param name="key">The secret key for <see cref="AesPmac"> authentication.</param>
public AesPmac(byte[] key)
{
if (key == null)
{
throw new ArgumentNullException(nameof(key));
}
aes = Utils.CreateAes(CipherMode.ECB);
encryptor = aes.CreateEncryptor(key, null);
byte[] temp = new byte[BlockSize];
encryptor.TransformBlock(temp, 0, BlockSize, temp, 0);
for (int i = 0; i < l.Length; ++i)
{
l[i] = (byte[])temp.Clone();
Utils.Multiply(temp);
}
inv = (byte[])l[0].Clone();
int lastBit = inv[BlockSize - 1] & 1;
for (int i = BlockSize - 1; i > 0; --i)
{
int carry = Subtle.ConstantTimeSelect(inv[i - 1] & 1, 0x80, 0);
inv[i] = (byte)((inv[i] >> 1) | carry);
}
inv[0] >>= 1;
inv[0] ^= (byte)Subtle.ConstantTimeSelect(lastBit, 0x80, 0);
inv[BlockSize - 1] ^= (byte)Subtle.ConstantTimeSelect(lastBit, Constants.R >> 1, 0);
}
public static void Multiply(byte[] input)
{
Debug.Assert(input.Length == Constants.BlockSize);
int carry = input[0] >> 7;
for (int i = 0; i < Constants.BlockSize - 1; ++i)
{
input[i] = (byte)((input[i] << 1) | (input[i + 1] >> 7));
}
byte last = input[Constants.BlockSize - 1];
input[Constants.BlockSize - 1] = (byte)((last << 1) ^ Subtle.ConstantTimeSelect(carry, Constants.R, 0));
}
