requests that are generated by the browser, and thus cannot glean timing information from them. Scale The measure of scale that we evaluate is the expected total number of appearances that each jondo makes on all paths at any point in time. For example, if a jondo occupies two positions on one path and one position on another, then it makes a total of three appearances on these paths. Theorem : In a crowd of size n, the expected total number of appearances that any jondo makes on all paths is Each jondo's expected number of appearances on paths is virtually constant as a function of the size of the crowd. This suggests that crowds should be able to grow quite large. Attacks Crowds provides perfect anonymity against a corrupt receiver (i.e. see Degree of anonymity) as all members appear equally likely to have been the initiator. As we showed against collaborating corrupt nodes Crowds provides probable innocence as long as (see the paper for the derivation of this), and provides a degree of anonymity . Against the predecessor attack Crowds succumbs in ; this attack works by a corrupt node retaining the previous hop in the path, as this will be the sender more than any other node over the rounds of rebuilding the network it will become apparent who the initiator is. Reiter and Rubin mention this and recommend long (and if possible infinite) time between path reformations (caused when a node in the path leaves the network). Crowds is unable to protect against a global eavesdropper as it cannot use encryption on the links, this is because each node in Crowds is able to communicate with every other node (a fully connected graph), because of this setting up symmetric keys requires pairwise keys; this is too large of a number to be feasible. Against a local eavesdropper again Crowds provides no protection as the eavesdropper will see a message coming out of a node that did not enter, and this positively identifies the node as the sender. See also Onion routing Tor (anonymity network) Degree of anonymity Mix network References Further reading External links Anonymity Bibliography Cryptology ePrint Archive Routing software Anonymity networks