Optimistic protocol for certified electronic mail with verifiable TTP

A large number of certified email proposals have been published over the last thirty years. Many use a trusted third party (TTP) to guarantee the core security property: fairness; however, the verifiability of this TTP has not received enough attention. In fact, we have not been able to find a complete proposal for optimistic certified email with verifiable TTP, which meets the fairness and timeliness requirements. Moreover, only a few papers discuss the deployment of the solutions proposed. Here, we present an optimistic protocol for certified electronic mail with a verifiable TTP. We prove its feasibility by discussing an implementation of the proposal that does not modify the core network for Internet mail and operates using the current standardized email protocols.