A Game-Theoretic Approach to IP Address Randomization in Decoy-Based Cyber Defense

Networks of decoy nodes protect cyber systems by distracting and misleading adversaries. Decoy defenses can be further enhanced by randomizing the space of node IP addresses, thus preventing an adversary from identifying and blacklisting decoy nodes over time. The decoy-based defense results in a time-varying interaction between the adversary, who attempts to identify and target real nodes, and the system, which deploys decoys and randomizes the address space in order to protect the identity of the real node. In this paper, we present a game-theoretic framework for modeling the strategic interaction between an external adversary and a network of decoy nodes. Our framework consists of two components. First, we model and study the interaction between the adversary and a single decoy node. We analyze the case where the adversary attempts to identify decoy nodes by examining the timing of node responses, as well as the case where the adversary identifies decoys via differences in protocol implementations between decoy and real nodes. Second, we formulate games with an adversary who attempts to find a real node in a network consisting of real and decoy nodes, where the time to detect whether a node is real or a decoy is derived from the equilibria of the games in first component. We derive the optimal policy of the system to randomize the IP address space in order to avoid detection of the real node, and prove that there is a unique threshold-based Stackelberg equilibrium for the game. Through simulation study, we find that the game between a single decoy and an adversary mounting timing-based attacks has a pure-strategy Nash equilibrium, while identification of decoy nodes via protocol implementation admits only mixed-strategy equilibria.