A Two-Phase Highly-Available Protocol for Online Validation of E-Tickets

highly available e-services, electronic tickets, online validation protocols E-ticket is an Internet service which, similarly to real-world tickets, gives their owners permission to enter a place of entertainment, use a means of transportation, or have access to some other Internet services. E-tickets can be stored in desktop computers or personal digital assistants for future use. Before being used, e-tickets have to be validated to prevent duplication, and ensure authenticity and integrity. This paper studies the e-ticket validation problem in contexts in which users cannot be trusted and servers may fail. The paper proposes formal definitions for the e-ticket validation problem, and shows that some intuitive guarantees cannot be implemented when failures may occur. The paper also presents two protocols for online validation of e-tickets.