Energy Analysis of Lightweight AEAD Circuits

The selection criteria for NIST's Lightweight Crypto Standardization (LWC) have been slowly shifting towards the lightweight efficiency of designs, given that a large number of candidates already establish their security claims on conservative, well-studied paradigms. The research community has accumulated a decent level of experience on authenticated encryption primitives, thanks mostly to the recently completed CAESAR competition, with the advent of the NIST LWC, the de facto focus is now on evaluating efficiency of the designs with respect to hardware metrics like area, throughput, power and energy. In this paper, we focus on a less investigated metric under the umbrella term lightweight, i.e. energy consumption. Quantitatively speaking, energy is the sum total electrical work done by a voltage source and thus is a critical metric of lightweight efficiency. Among the thirty-two second round candidates, we give a detailed evaluation of the ten that only make use of a lightweight or semi-lightweight block cipher at their core. We use this pool of candidates to investigate a list of generic implementation choices that have considerable effect on both the size and the energy consumption of modes of operation circuit, which function as an authenticated encryption primitive. Besides providing energy and circuit size metrics of these candidates, our results provide useful insights for designers who wish to understand what particular choices incur significant energy consumption in AEAD schemes. In the second part of the paper we shift our focus to threshold implementations that offer protection against first order power analysis attacks. There has been no study focusing on energy efficiency of such protected implementations and as such the optimizations involved in such circuits are not well established. We explore the simplest possible protected circuit: the one in which only the state path of the underlying block cipher is shared, and we explore how design choices like number of shares, implementation of the masked s-box and the circuit structure of the AEAD scheme affect the energy consumption.