  A Man-in-the-Middle (MiM) can collect over-the-air packets whether from a
mobile or a base station, process them, possibly modify them, and forward them
to the intended receiver. This paper exhibits the REVEAL protocol that can
detect a MiM, whether it has half duplex capability, full duplex capability, or
double full duplex capability. Protocol is based on synchronizing clocks
between the mobile and the base station, with the MiM being detected if it
interferes in the synchronization process. Once synchronized, the REVEAL
protocol creates a sequence of challenge packets where the transmission times
of the packets, their durations, and their frequencies, are chosen to create
conflicts at the MiM, and make it impossible for the MiM to function. We
implement the REVEAL protocol for detecting a MiM in 4G technology. We
instantiate a MiM between the 4G/5G base station and a mobile, and exhibit the
successful detection mechanisms. With the shared source code, our work can be
reproduced using open software defined cellular networks with off-the-shelf
devices
