Dynamic colour table: A novel S-box for cryptographic applications

Summary In cryptography, S-boxes play an important role in symmetric ciphers. S-boxes are used for substitution process to enable diffusion in encryption and decryption of the messages. In most of the conventional and modern symmetric ciphers, the S-boxes are of static in nature. It will never depend or vary with respect to the message or the key, but dynamic S-boxes are more resistant to linear and differential attacks when compared with the static S-boxes. In this paper, we propose the design of a new dynamic colour table (DCT) that can be used as S-box in symmetric ciphers and it depends upon a master key K. The same key can be used for encryption and decryption in symmetric ciphers. Dynamic colour table is a 64×4 table, having 256 entries. Each column of DCT has 64 unique values. The input to generate the DCT is 160 bit master key K. We have also developed a sub-key generation algorithm for generating the sub keys and 4 seeds from the master key of 160 bits. These 4 seeds are used to generate the random values in DCT. Dynamic colour table uses the alpha red green blue (ARGB) colour model concept for each entry. Our DCT is so lightweight in nature. Our new DCT have a wide range of applications such as it can be used as S-boxes in symmetric ciphers or it can be used as pseudorandom number generators. Finally, we show an implementation and the simulated results of DCT. The simulated results are used to analyse the strength of our DCT. The different criterions to verify that DCT has the characteristic of good S-box are nonlinearity, strong avalanche criterion, bit Independence criterion, differential approximation probability, and linear approximation probability. The performance is measured in terms of time complexity and security. The results show that our DCT is cryptographically stronger to use in various symmetric encryption algorithms.