The Optimal Implementation of Khudra Lightweight Block Cipher

Abstract

In this paper, we discuss the area and speed balance optimization of Khudra lightweight block cipher. There are three major ingredients. Firstly, because of the whole structure of the Khudra block cipher and its F-function is based on a Feistel structure, we make the main module that directly calls the F-function in the hardware optimization implementation. Secondly, through the clock control, the plaintext can be XORed with the key and the round constant under certain conditions. At the same time, the three rounds of the F-function are merged into one module, whose F-function module contains the F-function of the left and right branches of the algorithm. Thus, three rounds of operations can be completed with only one S-box, which can effectively reduce the number of registers and the number of iterations to increase the encryption and decryption rate. Finally, because of the particularity of key expansion in Khudra, we separately calculated the round key and stored its results in the register, which can effectively save the time of key expansion.