  Information leakage can have dramatic consequences on the security of
real-time systems. Timing leaks occur when an attacker is able to infer private
behavior depending on timing information. In this work, we propose a definition
of expiring timed opacity w.r.t. execution time, where a system is opaque
whenever the attacker is unable to deduce the reachability of some private
state solely based on the execution time; in addition, the secrecy is violated
only when the private state was entered "recently", i.e., within a given time
bound (or expiration date) prior to system completion. This has an interesting
parallel with concrete applications, notably cache deducibility: it may be
useless for the attacker to know the cache content too late after its
observance. We study here expiring timed opacity problems in timed automata. We
consider the set of time bounds (or expiration dates) for which a system is
opaque and show when they can be effectively computed for timed automata. We
then study the decidability of several parameterized problems, when not only
the bounds, but also some internal timing constants become timing parameters of
unknown constant values.
