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 digital 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.