From Unbalanced to Perfect: Implementation of Low Energy Stream Ciphers

Abstract

Low energy is an important aspect of hardware implementation. For energy-limited battery-powered devices, low energy stream ciphers can play an important role. In \texttt{IACR ToSC 2021}, Caforio et al. proposed the Perfect Tree energy model for stream cipher that links the structure of combinational logic circuits with state update functions to energy consumption. In addition, a metric given by the model shows a negative correlation with energy consumption, i.e., the higher the balance of the perfect tree, the lower the energy consumption. However, Caforio et al. didn\u27t give a method that eliminate imbalances of the unrolled strand tree for the existing stream ciphers. In this paper, based on the Perfect Tree energy model, we propose a new redundant design model that improve the balances of the unrolled strand tree for the purpose of reducing energy consumption. In order to obtain the redundant design, we propose a search algorithm for returning the corresponding implementation scheme. For the existing stream ciphers, the proposed model and search method can be used to provide a low-power redundancy design scheme. To verify the effectiveness, we apply our redundant model and search method in the stream ciphers (e.g., \texttt{Trivium} and \texttt{Kreyvium}) and conducted a synthetic test. The results of the energy measurement demonstrate that the proposed model and search method can obtain lower energy consumption