Risk-Based Optimization of Cryptoperiods to Minimize Impact of Data Siphoning Attacks on ICSs

Internal network and system reconnaissance is one of the first crucial stages of most cyber attacks, though it plays an especially critical role in attacks on complex industrial control systems (ICSs) that span both IT and OT environments. Frequently, besides device enumeration and scanning, a malicious ICS reconnaissance campaign will also involve siphoning of important operational in-transit data, which can provide the adversary with invaluable insights and information about the functioning of the target system. In this work, by specifically focusing on industrial systems that deploy OPC UA standard, we first give a brief overview of different data siphoning strategies possibly conducted by an adversary. We then discuss the important role of periodic encryption-key rotation (i.e., limiting of cryptoperiod length/duration) to minimize the ultimate risk and impact of data siphoning. We also point to the lack of clear guideline in industry standards and research literature on how cryptoperiod(s) assigned to an OPC UA security group should be determined/calculated. We then introduce our novel framework and tool for automatic risk-based optimal cryptoperiod calculation (ARC-C). We demonstrate the use and usefulness of this tool by applying it to a hypothetical but highly plausible Water Treatment Plant environment built on real-world models.