The system you describe is approximately a one-hop mix, with Tor layered in front of the mix to prevent the mix (the leader in your design) from learning who submitted which message. So the security against learning group membership will reduce to the security of Tor; the security against the leader learning who sent what reduces to the security of Tor; and the security against a third party learning who sent what reduces to breaking Tor *and* breaking a one-hop mix.
(Incidentally, there's an extensive literature on how to build mixes: it turns out that "delay a random interval" isn't optimal.) To answer your original question though, it would help to know the threat model! Tor will provide anonymity in this case so long as no adversary has compromised or controls enough of the network to observe a message as it enters and exits. But if an attacker sees the same message entering and exiting the tor network, they can (probabilistically) match them based on size and timing. This doesn't give the attacker a win against your protocol though (IIUC) unless they also defeat the leader's mixing. Other systems to look into here will come from the general anonymous communications literature. DC-nets are great for low-volume broadcast among a small number of participants, if you don't care about performance or DoS-robustness. Or since what you're talking about already incorporates a mix, you could look at other mix designs for ideas. Have a look through http://freehaven.net/anonbib if you haven't already. Best wishes, -- Nick _______________________________________________ tor-talk mailing list tor-talk@lists.torproject.org https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-talk
