Comprehensive Analysis of Supply Voltage Watermarking for Protection of Sensor Systems

Securing smart sensors in IoT or more general in automation applications is mostly seen and addressed from a networking viewpoint. While there is much research on how to make communication in sensor networks secure and prevent data manipulation during transmission, less attention is paid to the sensor itself that provides the actual measurement data. However, manipulation of the sensor can lead to serious malfunction of an automation system. Protection of the hardware side of a sensor is therefore desirable, but faces constraints related to cost or technical feasibility. In this paper, we investigate a simple watermarking scheme applied to the analog readout of a resistive sensor. Based on the example of a outside temperature sensor in a heating control, we analyze various attack scenarios involving voltage injection and determine the level of protection that can be achieved.

I. Introduction

Hardening IoT systems against attacks is one of the future requirements for the increasing spread of such systems in multiple application areas. In the domain of home automation systems we additionally face the challenge that IoT appliances need to be extremely low cost and lack an organized security supervision [1], [2]. In [3] we proposed a watermarking scheme that applies an analog watermark on the supply voltage to enable the system to detect manipulations of hardware attacks on the sensor itself. Using common microcontrollers this system can detect voltage saturation and voltage injection attacks on the ADC pins. The big advantage of the proposed system is that it does not require any additional hardware. In lab experiments we already demonstrated the characteristics of the system for selected scenarios as proof of concept.