Randomized Switching SAR (RS-SAR) ADC Protections for Power and Electromagnetic Side Channel Security

Abstract

Analog to digital converters (ADCs) are necessary in most Internet of Things (loT) devices, to link the physical analog world to digital computation. Physical side channel attacks (SCAs) have been used to reconstruct information processed within digital integrated circuits in a variety of applications, through power or electromagnetic (EM) traces [1]. Furthermore, power SCAs have successfully decoded the analog information converted within Successive Approximation Register (SAR) ADCs [2], [3]. Previous works have proposed initial protections, such as switched-capacitor current equalization for power SCAs [2], random dithering for the reference charge [3], or general power side channel security using a stacked digital low dropout array and random noise injection [4]. Whereas power SCAs require cutting the power trace and introducing a shunt resistor for measurement, EM SCAs can effectively perform non-invasive measurements external to packaging (Fig. 1). However, supply current equalization is not effective against localized EM SCAs, which can probe currents directly above the ADC circuitry.