  Today's cyber-physical systems face various impediments to achieving their
intended goals, namely, communication uncertainties and faults, relative to the
increased integration of networked and wireless devices, hinder the synchronism
needed to meet real-time deadlines. Moreover, being critical, these systems are
also exposed to significant security threats. This threat combination increases
the risk of physical damage. This paper addresses these problems by studying
how to build the first real-time Byzantine reliable broadcast protocol (RTBRB)
tolerating network uncertainties, faults, and attacks. Previous literature
describes either real-time reliable broadcast protocols, or asynchronous (non
real-time) Byzantine~ones.
  We first prove that it is impossible to implement RTBRB using traditional
distributed computing paradigms, e.g., where the error/failure detection
mechanisms of processes are decoupled from the broadcast algorithm itself, even
with the help of the most powerful failure detectors. We circumvent this
impossibility by proposing RT-ByzCast, an algorithm based on aggregating
digital signatures in a sliding time-window and on empowering processes with
self-crashing capabilities to mask and bound losses. We show that RT-ByzCast
(i) operates in real-time by proving that messages broadcast by correct
processes are delivered within a known bounded delay, and (ii) is reliable by
demonstrating that correct processes using our algorithm crash themselves with
a negligible probability, even with message loss rates as high as 60%.
