  Timed Intruder Models have been proposed for the verification of
Cyber-Physical Security Protocols (CPSP) amending the traditional Dolev-Yao
intruder to obey the physical restrictions of the environment. Since to learn a
message, a Timed Intruder needs to wait for a message to arrive, mounting an
attack may depend on where Timed Intruders are. It may well be the case that in
the presence of a great number of intruders there is no attack, but there is an
attack in the presence of a small number of well placed intruders. Therefore, a
major challenge for the automated verification of CPSP is to determine how many
Timed Intruders to use and where should they be placed. This paper answers this
question by showing it is enough to use the same number of Timed Intruders as
the number of participants. We also report on some preliminary experimental
results in discovering attacks in CPSP.
