private static void PackHeader(CryptoClient client, Span <byte> packet)
{
var key = client.ServerKey;
var randKey = _random.Next(0, 255);
packet[6] = (byte)randKey; // Set RandKey field
packet[7] = 0x06; // Set Packing field to 0x06 (don't change key)
packet[8] = CryptoCommon.MakeChecksum(packet, key); // Update the checkflag
// Encrypt packing
packet[7] = KeyTable.Table[(ushort)((randKey << 8) + packet[7])];
// Encrypt length
var length = (ushort)((KeyTable.Table[(ushort)(((packet[6] ^ packet[7]) << 8) + packet[1])] << 8)
+ KeyTable.Table[(ushort)(((packet[7] ^ key) << 8) + packet[0])]);
ByteUtil.CopyTo(packet, 0, length);
// Encrypt opcode
var opcode = (ushort)((KeyTable.Table[(ushort)(((packet[1] ^ key) << 8) + packet[3])] << 8)
+ KeyTable.Table[(ushort)(((packet[6] ^ packet[0]) << 8) + packet[2])]);
ByteUtil.CopyTo(packet, 2, opcode);
// Encrypt sequence
var sequence = (ushort)((KeyTable.Table[(ushort)(((packet[3] ^ packet[7]) << 8) + packet[5])] << 8)
+ KeyTable.Table[(ushort)(((packet[2] ^ key) << 8) + packet[4])]);
ByteUtil.CopyTo(packet, 4, sequence);
}
/// <summary>
/// This method is copied directly from the Trickster server.
///
/// My theory on what this method does is that it makes sure the first packet sent is valid.
/// If it's not valid, we can exit early as the server will know that it's an invalid client.
/// Perhaps someone's trying to send some trash data or connect with a non-client.
///
/// The Header object (at the time of a call to this function) is essentially a bunch
/// of fields within the raw packet.
/// </summary>
/// <param name="header">The Header object before decrypting the packet header.</param>
/// <param name="client">The current client session.</param>
/// <returns>Primitive packet validity flag</returns>
private static bool CheckHeader(Header header, CryptoClient client)
{
if (!client.IsFirstPacket)
{
return(true);
}
byte packing = header.Packing;
if (packing > 0xFu && (KeyTable.Table[(ushort)((header.RandKey << 8) + packing)] & 0xF) == 15)
{
// If that magic value is 15, we know this is a primitively "valid packet".
// We can update the session since we know the next packet is no longer the first packet.
client.IsFirstPacket = false;
return(true);
}
return(false);
}
public static void UpdateKey(CryptoClient client, int tail)
{
byte key = client.Key;
client.Key = (byte)(KeyTable.Table[((tail & 0xff) << 8) + key] + key);
}
private static void PackStream(CryptoClient client, ushort opcode, Span <byte> packet)
{
// Get the packet data only, from offset 9 to (len - 2)
var data = packet[9..^ 2];