So I'm just trying to understand the functioning of the Tor network from Robert Heaton fantastic article. My understanding is that the guaranty Tor tries to give is that no node knows which source IP is talking to which destination IP.
- The guard node knows the source IP but not the destination.
- The middle node doesn't know the source IP, neither the destination.
- The exit node knows the destination IP but not the source.
My question is: what is the purpose of the middle node in ensuring the guaranty? If I remove the middle node from the list above, neither the guard node nor the exit node know about both the source and destination IP, so the system still works.
Of course if I control both the guard and exit nodes at once, I could correlate the logs to construct the logs of a full circuit, but that is also true with 3 nodes if I also control the middle node. In this case, why stop at 3 nodes? The more nodes there are in the circuit, the less likely it is that one entity is controlling them all.