But there are two sorts of attack to keep in mind. Take PIR for example. PIR allows a client to download an item from a server without the server or any third party being able to determine the item obtained. At face value this means receive anonymity is automatically perfect with PIR. But these systems are still weak to traffic analysis. Let's say that the network consists of 100 people. One day Alice sends Bob 500 messages. Alice can watch the entire network externally. She notes that only one node obtained 500 messages for a given cycle, all other nodes obtained 1 or less messages. Now Alice cannot break the PIR to determine who Bob is, and even the server doesn't know who downloaded the messages sent to Bob. But due to the fact that only one node downloaded 500 messages, Alice can have a pretty damn good idea of who Bob is. So even though the PIR protects from some attacks (hell I don't even know what to call this class of attacks? cryptographic attacks?) it doesn't inherently protect from traffic analysis. But using PIR-like systems as a base allows us to focus on the remaining traffic analysis issues. Some of them are probably impossible to solve with pseudonymity. DC-nets are information theoretical perfect anonymity but even they can be broken by long term intersection attacks if the users are pseudonymous and the ideal conditions are not maintained indefinitely.