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Chapter 9 EigenTrust > 9.2 Reputation Systems - Pg. 85

EIGENTRUST 85 2. The system should maintain anonymity. That is, a peer's reputation should be associated with an opaque identifier (such as the peer's Gnutella username) rather than with an externally associated identity (such as a peer's IP address). 3. The system should not assign any profit to newcomers. That is, reputation should be obtained by consistent good behavior through several transactions, and it should not be advantageous for malicious peers with poor reputations to continuously change their opaque identifiers to obtain newcomer status. 4. The system should have minimal overhead in terms of computation, infra- structure, storage, and message complexity. 5. The system should be robust to malicious collectives of peers who know one another and attempt to subvert the system collectively. 9.2 REPUTATION SYSTEMS An important example of successful reputation management is the online auction system eBay [25]. In eBay's reputation system, buyers and sellers can rate each other after each transaction, and the overall reputation of a participant is the sum of these ratings over the last 6 months. This system relies on a centralized system to store and manage these ratings. In a distributed environment, peers may still rate each other after each transac- tion, as in the eBay system. For example, each time peer i downloads a file from