A novel approach for the development of the Twofish algorithm based on multi-level key space

Abstract

This paper presents a new modification of the Twofish algorithm for strengthening security. This is done by using two additional control keys during 16 rounds of the standard Feistel Encryption algorithm. Our proposed algorithm uses three keys in the encryption and decryption processes instead of only one key for controlling variable bit sizes of the blocks (either 1or 2, or 4 or 8 bits), which determine the state table numbers. These tables are constructed from the addition in a Galois field (GF(2n)) based on the block bit size to increase the complexity of the proposed algorithm. Results are evaluated based on the criteria of complexity, time encryption, throughput, National Institute of Standards and Technology (NIST), histogram analysis, Number of Pixel of Change Rate (NPCR) and Unified Average Changing Intensity (UACI). The simulation results show that our proposed algorithm exceeds the original algorithm in complexity, where it obtained (24,722,900) probabilities for 16 rounds. In addition, NIST tests and histogram analysis provide better results for our proposed algorithm compared with the original. Also, NPCR of our proposed Twofish is close to the ideal value of this standard. All these results prove that our modification of the Twofish algorithm makes it stronger against attacks by increasing its complexity.