Consider an environment in which many servers serve an even larger number of clients. It is required to meter the interaction between each server and the clients and in particular the number of clients that approached the server. An immediate application is to measure the popularity of web pages in order to decide on advertisement fees. The metering process should be efficient (even more efficient than micropayments) to all parties involved (clients, servers and the metering authority) and secure against fraud attempts. We present several such metering systems and discuss other scenarios where such auditing is useful. One application of these technique is for on-line petitions.
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