Crowds
This article refers to "a proposed anonymity network." For the psychological and sociological term referring to adolescent peer groups, see Crowds (adolescence).
Crowds is a proposed anonymity network for anonymous web browsing. The main idea behind Crowds anonymity protocol is to hide each user's communications by routing them randomly within a group of similar users. Neither the collaborating group members nor the end receiver can therefore be sure where in the group the packet originated. Crowds was designed by Michael K. Reiter and Aviel D. Rubin. It defends against internal attackers and a corrupt receiver, but provides no anonymity against a global attacker or a local eavesdropper (see "Crowds: Anonymity For Web Transactions"). Crowds is vulnerable to the predecessor attack; this was discussed in Reiter and Rubin's paper and further expanded in "The Predecessor Attack: An Analysis of a Threat to Anonymous Communications Systems" by Matthew K. Wright, Micah Adler, And Brian Neil Levine. Crowds introduced the concept of users blending into a crowd of computers.
Crowds uses and defines the following terms:
Crowds works by making each node seem equally likely to be the initiator of the message. As we said each node joins the network by starting a jondo (from "John Doe"), which is a small process that will forward and receive requests from other users. When the jondo is started all nodes in the network are informed of the new node's entrance, and will begin to select him as a forwarder. To actually send a message a node chooses randomly (with uniform probability) from all nodes in the network and forwards the message to them. Upon receiving the message the node flips a biased coin (with probability ) and if it lands heads forwards it to another random node, otherwise it forwards it to the final destination. Each node when forwarding to another node records the predecessor and in this way a tunnel is built, this is used for the communication between the sender and the receiver.
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