Privacy Leakages in Approximate Adders

TL;DR

This paper demonstrates that approximate adders in digital systems can leak user privacy by revealing chip identity through erroneous outputs caused by process variation, especially under over-scaled operating conditions.

Contribution

It is the first study to show privacy leakages in approximate computing, analyzing how different adder types can identify chips and quantifying the effects of over-scaling and noise.

Findings

Identification of chip type is possible through output analysis.

Privacy leakage varies with over-scaling and noise levels.

Different adder architectures have varying susceptibility to identification.

Abstract

Approximate computing has recently emerged as a promising method to meet the low power requirements of digital designs. The erroneous outputs produced in approximate computing can be partially a function of each chip's process variation. We show that, in such schemes, the erroneous outputs produced on each chip instance can reveal the identity of the chip that performed the computation, possibly jeopardizing user privacy. In this work, we perform simulation experiments on 32-bit Ripple Carry Adders, Carry Lookahead Adders, and Han-Carlson Adders running at over-scaled operating points. Our results show that identification is possible, we contrast the identifiability of each type of adder, and we quantify how success of identification varies with the extent of over-scaling and noise. Our results are the first to show that approximate digital computations may compromise privacy. Designers of future approximate computing systems should be aware of the possible privacy leakages and decide whether mitigation is warranted in their application.