I've been working on a p2p system on and off for the last couple years.
I think this is the first time I ever mentioned it online and that was over 2 years ago. At the time I was trying to figure out how to have private networks... It turns out the answer is not too difficult.
1) Each network has a password.
2) Take the password and your IP address and hash them.
3) Send the hash to the other people in the network.
4) The other people know the password and they know your IP address. They hash them and compare it with the hash that you sent. If it matches then you are accepted in the network.
Of course, that doesn't deal with the case where your ISP is listenning to your traffic. Your ISP can just test all the words in the dictionary until they get one that leads to the hash you sent. But I can accept that for now, I guess.
Any way... I had hoped to get a text based demo version ready and submit a paper for CodeCon, but I won't be able to make it in time.
That's too bad...