L“ndeniable Billing in 310bile Colnnlunication

In the current mobile communication networks, users have to trtistnetwork operators to make correct. charges over the cds they made. There islack of evidence to resolve possible disputti+ over thenurnberofcdls and the duration of each cd. Such a concern may grow when users roam among different network operators. This paper proposes an efficient solution to undeniable b]~ng when a mobile user roams into foreign networks. This is achieved by the combination of digitd signature and hash-chaining techniques. Mobile users need to submit a digitd signature when requesting a cd and release chained h~<h vahtes during the session so that the cd and its duration are undeniable. Our mechanism is tight-weighted regarding the storage requirement and comput ation overhead~ on a mobile user, and is apphcable for mobile phone users equipped with a smart card. Ke~ords: undeniable bi~ng, mobile communication se curity, non-repudiation, cryptographic protocol