Doubly-Anonymous Crowds: Using Secret-Sharing to achieve Sender- and Receiver-Anonymity

Anonymous communication is usually achieved by using overlay networks and public-key cryptography. Besides well-established protocols, based on onion routing, various competing solutions have been proposed in the literature. In this work we extend the Crowds system by providing sender and adjustable receiver anonymity. Our solution is robust against a coalition of passive adversaries having intermediate nodes in the network conquered in an attempt to discover the sender and receiver of an observed communication. Absolute privacy for the receiver is achievable asymptotically in the size of the network, which is beyond the control of a sender. We demonstrate that a certain level of anonymity is achievable in finitely large networks and under full control of the sender.