public MabiCipherEngine(MabiKeystreamGenerator keyGen)
{
_keyGen = keyGen;
_keystream = new byte[128];
for (var i = 31; i >= 0; i--)
{
BitConverter.GetBytes(_keyGen.GetNextKey()).CopyTo(_keystream, i * 4);
}
_idx = 31;
}
public MabiCipherEngine(MabiKeystreamGenerator keyGen)
{
_keyGen = keyGen;
_keystream = new byte[128];
for (var i = 31; i >= 0; i--)
{
BitConverter.GetBytes(_keyGen.GetNextKey()).CopyTo(_keystream, i * 4);
}
_idx = 31;
}
public void ProcessPacket(byte[] packet, int offset, int len)
{
len -= 4;
int i;
var tmpIdx = _idx * 4; // Convert idx into a byte index
for (i = offset; i < len; i += 4)
{
var j = tmpIdx & 0x1F; // Convert tmpIdx into a value [0, 32)
// this is, in effect, the first 32 bytes of the keystream
tmpIdx += 4; // Advance the counter by 4
packet[i] ^= _keystream[j];
packet[i + 1] ^= _keystream[j + 1];
packet[i + 2] ^= _keystream[j + 2];
packet[i + 3] ^= _keystream[j + 3];
}
len += 4;
// Process the final block, which may not be a multiple of 4
while (i < len)
{
packet[i] ^= _keystream[tmpIdx & 0x7F]; // Convert the counter into a value [0, 128)
// this is, in effect, anywhere along the key
i++;
tmpIdx++;
}
// Replace a subset of the key. Idx will always be on the range [0, 32)
// So this effectively changes 4 bytes of the "Main" key and doesn't touch the remainder
BitConverter.GetBytes(_keyGen.GetNextKey()).CopyTo(_keystream, _idx);
if (_idx == 0)
{
_idx = 31;
}
else
{
_idx--;
}
}
