[samizdatum]

Because Alice already knows the NSA didn't pay, the game effectively reduces to a two-participant model. Obviously, playing this game with only one other participant would provide no anonymity at all. n-1 colluders can deanonymize any DC network with group size n.

Another fundamental problem with DC networks is that a single malicious participant can completely disrupt communication, and the inherent anonymity of the protocol means detecting malicious actors is very difficult. Chaum introduces the idea of "trap rounds" that can be used to slowly exclude bad actors, but in actual use, trap rounds are rather inelegant and impractical.

Herbivore http://www.cs.cornell.edu/people/egs/papers/herbivore-tr.pdf is an implementation of DC networks that circumvents some of these problems by sorting participants into randomized groups of ~k participants, where k is a network-wide anonymity set constant. It avoids collusion by disallowing participants to choose which k-sized bucket they end up in, and limits Sybil attacks by requiring proof-of-work to join the network.