A methodology for verification of digital items in fair exchange protocols with active trustee

Fair exchange constitutes a fundamental mechanism for electronic commerce. Fair exchange assumes that it is possible to verify the correctness of the digi- tal items to be exchanged. However, when an item is indescribable, i.e., it cannot be formally specified, its verification becomes difficult, if not impossible. This hinders a practical deployment of fair exchange. We propose a methodology for the verification of indescribable digital items. The methodology allows a participant in a fair exchange protocol to personally verify the indescribable item without giving him any practical advantage over the other participant, and therefore without violating the fairness imposed by the protocol.