Secure and Eecient Metering

We consider an environment in which many servers serve an even larger number of clients (e.g. the web), and it is required to meter the interaction between servers and clients. More speciically, it is desired to count the number of clients that were served by a server. A major possible application is to measure the popularity of web pages in order to decide on advertisement fees. The metering process must be very eecient and should not require extensive usage of any new communication channels. The metering should also be secure against fraud attempts by servers which innate the number of their clients and against clients that attempt to disrupt the metering process. We suggest several secure and eecient constructions of metering systems, based on eecient cryptographic techniques. They are also very accurate and can preserve the privacy of the clients.