O2TR: Offline OTR messaging system under network disruption

Abstract

Providing a secure and efficient communication system under network disruption without a trusted third party remains a challenging issue. To develop a secure and efficient system in such situations, we extend the conventional Off-The-Record (OTR) protocol into a new protocol named offline OTR (O2TR). O2TR provides end-to-end security between users without requiring the assumption that they are persistently connected to each other. To show the feasibility of the proposed protocol, we implemented a prototype to support O2TR based on the Gajim XMMP instant messaging platform. Our experiments showed that O2TR can be used reliably even when the corresponding network party is temporarily broken down. Moreover, O2TR provides an efficient way to resume private sessions which is about 34% faster than the original OTR. We also proved the secrecy of O2TR using an automated verification tool called AVISPA. © 2018 Elsevier Ltd