An Efficient VLSI Implementation of the SMS4 Cipher Using a Twisted BDD S-Box Architecture

SMS4 is a 128-bit block cipher that plays a key role in the WAP1 standard, primarily used for securing data packets within wireless local area networks (WLANs). This study begins by analyzing multiple S-box circuit designs, ultimately identifying the twisted Binary Decision Diagram (BDD) with m-4 configuration as the most efficient in terms of speed. Building upon this finding, a high-speed VLSI implementation of the SMS4 cipher was developed using the twisted BDD S-box. The resulting design demonstrated maximum operating frequencies exceeding 200 MHz on SMIC 0.18 µm CMOS technology and 100 MHz on Chartered 0.35 µm CMOS technology.