Nonrepudiation Protocols in Cloud Systems

A nonrepudiation protocol from a sender S to a set of potential receivers {R1, R2, ... , Rn} performs two functions. First, this protocol enables S to send to every potential receiver Ri a copy of file F along with a proof that can convince an unbiased judge that F was indeed sent by S to Ri. Second, this protocol also enables each Ri to receive from S a copy of file F and to send back to S a proof that can convince an unbiased judge that F was indeed received by Ri from S. When a nonrepudiation protocol from S to {R1, R2, ... , Rn} is implemented in a cloud system, the communications between S and the set of potential receivers {R1, R2, ... , Rn} are not carried out directly. Rather, these communications are carried out through a cloud C. In this paper, we present a nonrepudiation protocol that is implemented in a cloud system and show that this protocol is correct. We also show that this protocol has two clear advantages over nonrepudiation protocols that are not implemented in cloud systems.