Requirements for secure wireless time transfer

Time transfer is the backbone of all technologies that require synchronization between stations. Wireless time transfer protocols generally employ simple and convenient one-way communication for synchronization of different nodes. However, it is argued that all one-way wireless time transfer protocols are fundamentally vulnerable to replay attacks that compromise timing information. Necessary conditions for security of a two-way time transfer protocol are proposed and proved by contradiction. Furthermore, an example compliant system is presented in detail. The uncertainty in estimation of tropospheric delay using common climatological models is studied and its effect on the accuracy of one-way time transfer and security of two-way time transfer is presented. Analysis of these models suggest they are adequate for nanosecond-level accurate time transfer over links that are shorter than 10 km, but more sophisticated weather estimation techniques are needed if this accuracy is to be achieved over long distances.