Lightweight Cryptographic S-Boxes Based on Efficient Hardware Structures for Block Ciphers

This paper presents four low-cost substitution boxes (S-boxes), including two 4-bit S-boxes called S1 and S2 and two 8-bit S-boxes called SB1 and SB2, which are suitable for the development of lightweight block ciphers. The 8-bit SB1 S-box is constructed based on four 4-bit S-boxes, multiplication by constant 0x2 in the finite field F24 , and field addition operations. Also, the proposed 8-bit S-box SB2 is composed of five permutation blocks, two 4-bit S-boxes S1 and one 4-bit S-box S2, multiplication by constant 0x2, and addition operations in sequence. The proposed structures of the S-box are simple and low-cost. These structures have low area and low critical path delay. The cryptographic strength of the proposed S-boxes is analyzed by studying the properties of S-box such as nonlinearity, differential uniformity (DU), strict avalanche criterion (SAC), algebraic degree (AD), differential approximation probability (DAP), and linear approximation probability (LAP) in SAGE. The hardware results in 180 nm CMOS technology show the proposed S-boxes are comparable in terms of security properties, area, delay, and area×delay with most of the famous S-boxes.