/// <summary>
/// Decrypts data from server-side packets (sent from servers to clients.)
/// </summary>
/// <param name="source">The encrypted packet data.</param>
/// <param name="key">Key to decrypt with.</param>
/// <returns>The decrypted packet data.</returns>
/// <exception cref="ArgumentOutOfRangeException">
/// Thrown if the key is invalid or the packet data is too short.
/// </exception>
public static byte[] Decrypt(byte[] source, byte key)
{
if (key >= 0x10)
{
throw new ArgumentOutOfRangeException(nameof(key), $"Key too large ({key} >= 0x10)");
}
if (source.Length < 8)
{
throw new ArgumentOutOfRangeException(nameof(source), $"Packet too small ({source.Length} < 8)");
}
var oracleByte = CryptoOracle.CryptTable2[(key << 8) + source[0]];
var buffer = (byte[])source.Clone();
buffer[7] ^= oracleByte;
for (var i = 10; i < source.Length; i++)
{
buffer[i] ^= buffer[i - 4];
}
var compressedData = new byte[source.Length - 8];
Array.Copy(buffer, 8, compressedData, 0, source.Length - 8);
return(MiniLzo.Decompress(compressedData));
}
/// <summary>
/// Encrypts data for server-side packets (sent from servers to clients.)
/// </summary>
/// <param name="source">The decrypted packet data.</param>
/// <param name="key">Key to encrypt with.</param>
/// <param name="salt">Random salt value to encrypt with.</param>
/// <returns>The encrypted packet data.</returns>
/// <exception cref="ArgumentOutOfRangeException">
/// Thrown if an invalid key is specified.
/// </exception>
public static byte[] Encrypt(byte[] source, byte key, byte salt)
{
if (key >= 0x10)
{
throw new ArgumentOutOfRangeException(nameof(key), $"Key too large ({key} >= 0x10)");
}
var oracleIndex = (key << 8) + salt;
var compressedData = MiniLzo.Compress(source);
var buffer = new byte[compressedData.Length + 8];
var pLen = buffer.Length - 3;
var u = source.Length;
var x = (u + u / 255) & 0xff;
var v = (u - x) / 255;
var y = (v + v / 255) & 0xff;
var w = (v - y) / 255;
var z = (w + w / 255) & 0xff;
buffer[0] = salt;
buffer[1] = (byte)((pLen >> 0) & 0xFF);
buffer[2] = (byte)((pLen >> 8) & 0xFF);
buffer[3] = (byte)(CryptoOracle.CryptTable1[oracleIndex] ^ CryptoOracle.CryptTable2[oracleIndex]);
buffer[5] = (byte)z;
buffer[6] = (byte)y;
buffer[7] = (byte)x;
Array.Copy(compressedData, 0, buffer, 8, compressedData.Length);
for (var i = buffer.Length - 1; i >= 10; i--)
{
buffer[i] ^= buffer[i - 4];
}
buffer[7] ^= CryptoOracle.CryptTable2[oracleIndex];
return(buffer);
}
