  Swarm robotics is the study of how a large number of relatively simple robots
can be designed so that a desired collective behaviour emerges from the local
interactions among robots and between the robots and their environment. While
many aspects of a swarm may be modelled as various types of ad hoc networks,
and accordingly many aspects of security of the swarm may be achieved by
conventional means, here we will focus on swarm emergent behaviour as something
that most distinguishes swarm robotics from ad hoc networks. We discuss the
challenges emergent behaviour poses on communications security, and by
classifying a swarm by types of robots, types of communication channels, and
types of adversaries, we examine what classes may be secured by traditional
methods and focus on aspects that are most relevant to allowing emergent
behaviour. We will examine how this can be secured by ensuring that
communication is secure. We propose a simple solution using hash chains, and by
modelling swarm communications using a series of random graphs, we show that
this allows us to identify rogue robots with a high probability.
