Anonymous communication has received considerable attention to protect privacy in many applications such as anonymous web browsing [1,2], email [3], and voting [4]. Depending upon the applications, anonymous communication may hide one or more kinds of the following information from adversaries: (1) the linkage between messages and their senders/ recipients; (2) the linkage between two communication parties; (3) activities of sending or/ and receiving messages. Anonymous communication can protect privacy and the right of free speech/opinion. It can be utilized to access censored contents as well [5].