A Fair Non-repudiation Protocol

A fair non-repudiation protocol should not give the sender of a message an advantage over the receiver, or vice versa. We will present a fair non-repudiation protocol that requires a Trusted Third Party but attempts to minimize its involvement in the execution of the protocol. We will draw particular attention to the nonstandard use of encryption in our protocol and discuss some aspects of its formal verification. 1. Introduction Accountability is an important aspect of information security. In a distributed communication environment, we may therefore want to prevent entities from denying that they have sent or received certain messages. The goal of a non-repudiation service is to collect, maintain, make available, and validate irrefutable evidence regarding the transfer of a message from the originator to the recipient, possibly involving the service of a trusted third party called the Delivery Agent. We distinguish between the following non-repudiation services [8]. ffl Non-repudiat...