private Blowfish DeduceEncryptionKey(byte[] packet, int pos, int length)
{
ulong guessedNullBlock = 0;
// This is possible because block cipher mode of operation implemented in FFXIV is ECB mode and most of packets are filled with 0x00 byte.
// (actually, there's so many bytes are filled with 0x00 that it's enough to inspect the first packet sent from the server.)
//
// We know that the encryption key is derived from "keyPhrase", "timestamp" and "gameVersion".
// where "keyPhrase" and "timestamp" are sent as a plaintext in the initial handkeshake phase.
// Only thing not sent off the wire is the "gameVersion" component but this component can be brute forced in a reasonable time
// and verify the key by exploiting the fact that ECB mode lacks diffusion.
//
// https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Electronic_Codebook_(ECB)
{
var processor = new BlockProcessor();
processor.Process(packet, pos, length);
guessedNullBlock = processor.GetHighestKey();
}
for (var gameVer = 1000; gameVer <= 65000; gameVer += 10)
{
var key = LobbyKeyHelper.MakeKey(_initPacket, (ushort)gameVer);
var blowfish = new Blowfish(key);
var nullBlock = new byte[8];
blowfish.Encipher(nullBlock, 0, 8);
var attempedBlock = BitConverter.ToUInt64(nullBlock, 0);
if (attempedBlock == guessedNullBlock)
{
return(blowfish);
}
}
// Failed to guess a key for whatever reason; just use hardcoded key as a fallback.
var fallbackKey = LobbyKeyHelper.MakeKey(_initPacket, FallbackGameVersion);
return(new Blowfish(fallbackKey));
}
public LobbyEncryptionProvider(byte[] initPacket)
{
EncKey = MakeKey(BitConverter.ToUInt32(initPacket, 116), initPacket.Skip(52).TakeWhile(x => x != 0x00).ToArray());
_blowfish = new Blowfish(EncKey);
}