Microcredits for Verifiable Foreign Service Provider Metering

With the explosive growth of mobile communications, users may often access value-added services through foreign service providers. These providers will interact directly with users, later providing details to a user’s home service provider regarding the services rendered; the home service provider, in turn, bills the user. One critical concern is that the foreign service provider might inflate the usage figures it furnishes to the home service provider. In this paper, we address this issue using a microcredit scheme. The scheme is efficient as the verification time required by the home service provider is only logarithmic in the number of microcredit transactions, and the verification time required by the foreign service provider is constant. Moreover, the communication complexity per microcredit transaction between the user and foreign service provider is also constant. The scheme uses QuasiModo trees, which have been previously applied to certificate revocation. It improves upon previous chain-based proposals and their tree-based analogues. As a byproduct, our scheme yields a micropayment protocol which is an improvement over tree schemes with respect to both communication complexity and time complexity (in both cases by a factor of approximately 2, amortized).