Determine if cross circuit timing attacks work, despite sending only one packet. The problem: clients keep muliple circuits open, even while they are not in use. Imagine 1 is an attacker controller node and 0 is a good node. A clients set of open circuits may look as follows: 1 - 0 - 0 -> null 0 - 1 - 0 -> null 0 - 0 - 1 -> destination when Tor is exited, a shut down packet is sent through each open circuit. I propose that a timing attack on the shut down packet can be used to link traffic across multiple circuits, allowing the attacker who owns the '1' nodes to link the client to destination, despite not being able to observe the traffic on entry and exit. This is now recognized as a theoretical attack, however there is some amount of debate as to if it will work on the deployed Tor network. On a Tor network with a single user, it is certain to work. With as many users as there are on the current Tor network, some people think noise may prevent this attack from working with the single shut down packet. I strongly believe that the attack will work on the deployed Tor network, however there has not been any research done on this attack to date.