private byte[] Expand(byte[] key)
{
int expandedKeyLength = LengthAfterExpansion(key.Length);
_expandedKey = new List <byte>(key);
int iteration = 1;
while (_expandedKey.Count < expandedKeyLength)
{
byte[] lastFourBytes = _expandedKey.LastElements(4);
lastFourBytes = lastFourBytes.ShiftToLeft();
lastFourBytes = AesSBox.Transform(lastFourBytes);
Rcon.Apply(lastFourBytes, iteration);
IEnumerable <byte> fourBytes = _expandedKey.GetRange(_expandedKey.Count - key.Length, 4);
lastFourBytes = lastFourBytes.XOR(fourBytes);
_expandedKey.AddRange(lastFourBytes);
for (int i = 0; i < 3; i++)
{
lastFourBytes = _expandedKey.LastElements(4);
fourBytes = _expandedKey.GetRange(_expandedKey.Count - key.Length, 4);
lastFourBytes = lastFourBytes.XOR(fourBytes);
_expandedKey.AddRange(lastFourBytes);
}
if (key.Length == 32 && _expandedKey.Count < 240)
{
lastFourBytes = _expandedKey.LastElements(4);
lastFourBytes = AesSBox.Transform(lastFourBytes);
fourBytes = _expandedKey.GetRange(_expandedKey.Count - key.Length, 4);
lastFourBytes = lastFourBytes.XOR(fourBytes);
_expandedKey.AddRange(lastFourBytes);
}
int repeat = 0;
if (key.Length == 24 && _expandedKey.Count < 208)
{
repeat = 2;
}
else if (key.Length == 32 && _expandedKey.Count < 240)
{
repeat = 3;
}
for (int i = 0; i < repeat; i++)
{
lastFourBytes = _expandedKey.LastElements(4);
fourBytes = _expandedKey.GetRange(_expandedKey.Count - key.Length, 4);
lastFourBytes = lastFourBytes.XOR(fourBytes);
_expandedKey.AddRange(lastFourBytes);
}
iteration++;
}
return(_expandedKey.ToArray());
}
public static byte[][] SubBytes(byte[][] array)
{
return(AesSBox.Transform(array));
}