  Security can be seen as an optimisation objective in NoC resource management,
and as such poses trade-offs against other objectives such as real-time
schedulability. In this paper, we show how to increase NoC resilience against a
concrete type of security attack, named side-channel attack, which exploit the
correlation between specific non-functional properties (such as packet
latencies and routes, in the case of NoCs) to infer the functional behaviour of
secure applications. For instance, the transmission of a packet over a given
link of the NoC may hint on a cache miss, which can be used by an attacker to
guess specific parts of a secret cryptographic key, effectively weakening it.
  We therefore propose packet route randomisation as a mechanism to increase
NoC resilience against side-channel attacks, focusing specifically on the
potential impact of such an approach upon hard real-time systems, where
schedulability is a vital design requirement. Using an evolutionary
optimisation approach, we show how to effectively apply route randomisation in
such a way that it can increase NoC security while controlling its impact on
hard real-time performance guarantees. Extensive experimental evidence based on
analytical and simulation models supports our findings.
