I'm not 100% certain this is possible, but you guys just let me know if I've got the technicality messed up.

Here's the case:
I have a java applet (no it's not runescape) working with a TCP connection over port 499. I can see from tcpick(ing) that there's an authentication proces, which makes it hard for me to simply open a telnet connection to the server (If I do so it prompts me for a handshake, but I don't know the encoding, so I dont know how to respond).

What I am interested in doing is - after the authentication has happened - break into the socket connected and be able to send my own packets to the server/applet through the existing connection.

How should I approach that, and what tool could I use?

Thank you