Knowingly or unknowingly, we interact with hundreds of networked-embedded devices in our day-to-day lives such as mobile devices, electronic households, medical equipment, automobiles, media players, and many more. This increased dependence of our lives on the networked-embedded devices, nevertheless, has raised serious security concerns. In the past, security of embedded systems was not a major concern as these systems were a stand-alone network that contained only trusted devices with little or no communication to the external world. One could execute an attack only with a direct physical or local access to the internal embedded network or to the device. Today, however, almost every embedded device is connected to other devices or the external world (e.g., the Cloud) for advanced monitoring and management capabilities. On one hand, enabling networking capabilities paves the way for a smarter world that we currently live in, while on the other hand, the same capability raises severe security concerns in embedded devices. Recent attacks on embedded device product portfolios in the Black Hat and Defcon conferences has identified remote exploit vulnerabilities (e.g., an adversary who exploits the remote connectivity of embedded devices to launch attacks such as privacy leakage, malware insertion, and denial of service) as one of the major attack vectors. A handful of research efforts along the lines of traditional security defenses have been proposed to enhance the security posture of these networked devices. These solutions, however, do not entirely solve the problem and we therefore argue the need for a light weight intrusion-defense capability within the embedded device.
In particular, we observe that the networking capability of embedded devices can indeed be leveraged to provide an in-home secure proxy server that monitors all the network traffic to and from the devices. The proxy server will act as a gateway performing policy based operations on all the traffic to and from the interconnected embedded devices inside the household. In order to do so, the proxy server will implement an agent based computing model where each embedded device is required to run a light weight checker agent that periodically reports the device status back to the server; the server verifies the operation integrity and signals back the device to perform its normal functionality. A similar approach is proposed Ang Cui and Salvatore J. Stolfo’s 2011 paper, “Defending Embedded Systems with Software Symbiotes,” where a piece of software called Symbiote is injected into the device’s firmware that uses a secure checksum-based approach to detect any malicious intrusions into the device.
In contrast to Symbiote, we exploit lightweight checker agents at devices that merely forward device status to the server and all the related heavy computations are offloaded to the proxy server, which in turn proves our approach computationally efficient. Alternatively, the proposed model incurs a very small computational overhead in gathering and reporting critical device status messages to the server. Also, the communication overhead can be amortized under most circumstances as the sensor data from the checker agents can be piggybacked to the original data messages being transferred between the device and the server. Our model, as what’s described in the aforementioned Cui and Stolfo paper, can be easily integrated with legacy embedded devices as the only modification required to the legacy devices is a “firmware upgrade that includes checker agents.”
To complete the picture, we propose an additional layer of security for modern embedded devices by designing an AuditBox, as in the article, “Pillarbox,” by K. Bowers, C. Hart, A. Juels, and N. Triandopoulos. It keeps an obfuscated log of malicious events taking place at the device which are reported back to the server at predefined time intervals. This enables our server to act accordingly by either revoking the device from the network or by restoring it to a safe state. AuditBox will enforce integrity by being able to verify whether the logs at the device have been tampered with by an adversary who is in control of the device and covertness by hiding from an attacker with access to the device whether the log reports detection of malicious behavior. To realize these requirements, AuditBox will exploit the concept of forward secure key generation.
Embedded systems security is of crucial importance and the need of the hour. Along with the advancement in embedded systems technology, we need to put an equal emphasis on its security in order for our world to be truly a smarter place.
K. Bowers, C. Hart, A. Juels, & N. Triandopoulos, “Pillarbox: Combating Next-Generation Malware with Fast Forward-Secure Logging,” in Research in Attacks, Intrusions and Defenses, ser. Lecture Notes in Computer Science, A. Stavrou, H. Bos, and G. Portokalidis (Eds.), Springer, 2014, http://dx.doi.org/10.1007/978-3-319-11379-1_3.
A. Cui & S. J. Stolfo, “Defending embedded systems with software symbiotes,” in Proceedings of the 14th international conference on Recent Advances in Intrusion Detection (RAID’11), R. Sommer, D. Balzarotti, and G. Maier (Eds.), Springer-Verlag, 2011, http://dx.doi.org/10.1007/978-3-642-23644-0_19.
Marten van Dijk is an Associate Professor of Electrical and Computing Engineering at the University of Connecticut, with over 10 years research experience in system security both in academia and industry.
This essay appears in Circuit Cellar 297 (April 2015).