More Like this

1. Attack Recovery for Cyber-Physical Systems

   Kong, Fanxin; Wang, Zifan (October 2023, EAI International Conference on Security and Privacy in Cyber-Physical Systems and Smart Vehicles)

   Cyber-physical systems (CPSs) rely on computing components to control physical objects, and have been widely used in real-world life-critical applications. However, a CPS has security risks by nature due to the integration of many vulnerable subsystems, which adversaries exploit to inflict serious consequences. Among various attacks, sensor attacks pose a particularly significant threat, where an attacker maliciously modifies sensor measurements to drift system behavior. There is a lot of work in sensor attack prevention and detection. Nevertheless, an essential problem is overlooked: recovery--what to do after detecting a sensor attack, which needs to safely and timely bring a CPS back. We aim to highlight the need to investigate this problem, outline its four key challenges, and provide a brief overview of initial solutions in the field. 

   more » « less
2. Learn-to-Respond: Sequence-Predictive Recovery from Sensor Attacks in Cyber-Physical Systems

   https://doi.org/10.1109/RTSS59052.2023.00017  

   Liu, Mengyu; Zhang, Lin; Phoha, Vir V.; Kong, Fanxin (December 2023, IEEE Real-Time Systems Symposium (RTSS))

   While many research efforts on Cyber-Physical System (CPS) security are devoted to attack detection, how to respond to the detected attacks receives little attention. Attack response is essential since serious consequences can be caused if CPS continues to act on the compromised data by the attacks. In this work, we aim at the response to sensor attacks and adapt machine learning techniques to recover CPSs from such attacks. There are, however, several major challenges. i) Cumulative error. Recovery needs to estimate the current state of a physical system (e.g., the speed of a vehicle) in order to know if the system has been driven to a certain state. However, the estimation error accumulates over time in presence of compromised sensors. ii) Timely response. A fast response is needed since slow recovery not only comes with large estimation errors but also may be too late to avoid irreparable consequences. To address these challenges, we propose a novel learning-based solution, named sequence-predictive recovery (or SeqRec). To reduce the estimation error, SeqRec designs the first sequence-to-sequence (Seq2Seq) model to uncover the temporal and spatial dependencies among sensors and control demands, and then uses the model to estimate system states using the trustworthy data logged in history. To achieve an adequate and fast recovery, SeqRec designs the second Seq2Seq model that considers both the current time step using the remaining intact sensors and the future time steps based on a given target state, and embeds the model into a novel recovery control algorithm to drive a physical system back to that state. Experimental results demonstrate that SeqRec can effectively and efficiently recover CPSs from sensor attacks. 

   more » « less
3. Real-time Attack-recovery for Cyber-physical Systems Using Linear-quadratic Regulator

   https://doi.org/10.1145/3477010  

   Zhang, Lin; Lu, Pengyuan; Kong, Fanxin; Chen, Xin; Sokolsky, Oleg; Lee, Insup (October 2021, ACM Transactions on Embedded Computing Systems)

   The increasing autonomy and connectivity in cyber-physical systems (CPS) come with new security vulnerabilities that are easily exploitable by malicious attackers to spoof a system to perform dangerous actions. While the vast majority of existing works focus on attack prevention and detection, the key question is “what to do after detecting an attack?”. This problem attracts fairly rare attention though its significance is emphasized by the need to mitigate or even eliminate attack impacts on a system. In this article, we study this attack response problem and propose novel real-time recovery for securing CPS. First, this work’s core component is a recovery control calculator using a Linear-Quadratic Regulator (LQR) with timing and safety constraints. This component can smoothly steer back a physical system under control to a target state set before a safe deadline and maintain the system state in the set once it is driven to it. We further propose an Alternating Direction Method of Multipliers (ADMM) based algorithm that can fast solve the LQR-based recovery problem. Second, supporting components for the attack recovery computation include a checkpointer, a state reconstructor, and a deadline estimator. To realize these components respectively, we propose (i) a sliding-window-based checkpointing protocol that governs sufficient trustworthy data, (ii) a state reconstruction approach that uses the checkpointed data to estimate the current system state, and (iii) a reachability-based approach to conservatively estimate a safe deadline. Finally, we implement our approach and demonstrate its effectiveness in dealing with totally 15 experimental scenarios which are designed based on 5 CPS simulators and 3 types of sensor attacks. 

   more » « less
4. On the Security of Homomorphic Encryption on Approximate Numbers

   https://doi.org/10.1007/978-3-030-77870-5_23  

   Li, B.; Micciancio, D. (October 2021, Advances in Cryptology – EUROCRYPT 2021)

   Canteaut, A.; Standaert, F. (Ed.)

   We present passive attacks against CKKS, the homomorphic encryption scheme for arithmetic on approximate numbers presented at Asiacrypt 2017. The attack is both theoretically efficient (running in expected polynomial time) and very practical, leading to complete key recovery with high probability and very modest running times. We implemented and tested the attack against major open source homomorphic encryption libraries, including HEAAN, SEAL, HElib and PALISADE, and when computing several functions that often arise in applications of the CKKS scheme to machine learning on encrypted data, like mean and variance computations, and approximation of logistic and exponential functions using their Maclaurin series. The attack shows that the traditional formulation of IND-CPA security (or indistinguishability against chosen plaintext attacks) achieved by CKKS does not adequately capture security against passive adversaries when applied to approximate encryption schemes, and that a different, stronger definition is required to evaluate the security of such schemes. We provide a solid theoretical basis for the security evaluation of homomorphic encryption on approximate numbers (against passive attacks) by proposing new definitions, that naturally extend the traditional notion of IND-CPA security to the approximate computation setting. We propose both indistinguishability-based and simulation-based variants, as well as restricted versions of the definitions that limit the order and number of adversarial queries (as may be enforced by some applications). We prove implications and separations among different definitional variants, and discuss possible modifications to CKKS that may serve as a countermeasure to our attacks. 

   more » « less
5. Protecting Cyber-Physical System Testbeds from Red-Teaming/Blue-Teaming Experiments Gone Awry

   https://doi.org/10.1007/978-3-031-21280-2_8  

   Talukder, M.R.H.; Amin, M.A.; Ray, I (November 2022, Information Security Practice and Experience. ISPEC 2022. Lecture Notes in Computer Science)

   Su, C.; Gritzalis, D.; Piuri, V. (Ed.)

   Many cyber-physical systems (CPS) are critical infrastructure. Security attacks on these critical systems can have catastrophic consequences, putting human lives at risk. Consequently, it is very important to pace CPS systems to red-teaming/blue teaming exercises to understand vulnerabilities and the progression/impact of cyber attacks on them. Since it is not always prudent to conduct such security exercises on live CPS, researchers use CPS testbeds to conduct security-related experiments. Often, such testbeds are very expensive. Since attack scripts used in red-teaming/blue-teaming exercises are, in the strictest sense of the term, malicious in nature, there is a need to protect the testbed itself from these attack experiments that have the potential to go awry. Moreover, when multiple experiments are conducted on the same testbed, there is a need to maintain isolation among these experiments so that no experiment can accidentally or maliciously affect/compromise others. In this work, we describe a novel security architecture and framework to ensure protection of security-related experiments on a CPS testbed and at the same time support secure communication services among simultaneously running experiments based on well-formulated access control policies. 

   more » « less