Fundamentals

There are a few base concepts that you need to understand to fully grasp the whole network protocol from scratch.

Tokens

The ddnet protocol is 0.6.4 based which in teeworlds has no security tokens. But ddnet extended it with its own token protocol also known as TKEN extension. Because the magic bytes TKEN are used to indicated to the other party that the ddnet token extension is supported. The ddnet security tokens are 4 byte long and are placed at the very end of the packet. After the packet payload.
Be careful this is not the same security token that teeworlds 0.6.5 uses! See 0.6 tokens for more details.