Design and Security Evaluation of BSP-128: A Hybrid Blowfish and Serpent Inspired 128-Bit Block Cipher

Abstract

In this work, a new 128-bit block cipher (namely, Blowfish–Serpent Protocol 128-bit (BSP-128)) has been introduced that allows to improve the performance and implementation of an optimal compromise between security, performance, and implementation efficiency. The key size for the input and output for BSP-128 is also scalable at 128-bit blocks and keys with a length of up to 256 bytes, and the design conforms to the underlying scheme for AES. The BSP-128 algorithm uses a 16-round Feistel network similar to Blowfish and Serpent with multiple architectural improvements that aid the diffusion, so this cipher is much more robust against modern cryptanalysis techniques. The primary goal of BSP-128's design is to be resistant to both differential and linear cryptanalysis. Finally, the round structure was made even more powerful to better handle identified potential security vulnerabilities and targeted attack scenarios discovered in a subsequent internal analysis. By mixing substitution and permutation in the structure of the F–function, BSP-128 transforms from standard SP to a Substitution–Permutation–Substitution (SPS) type of model which boosts the avalanche effect. And we use in-place integer multiplication as a diffusion intermediate for additional mixing details to each round and to maintain the stable quality of the speed as well as security. While Blowfish's fixed-factor algorithm runs on 64-bit blocks and takes up a lot of memory for large lookup tables, BSP-128 automatically supports 128-bit blocks to avoid matching ciphertext attacks and achieve low memory consumption. This attribute of it adds a large value to its ability to work in limited hardware settings such as smart cards. The key expansion mechanism yields 786 bytes of subkeys, which are made from a P-array having 32 subkeys of 64 bits each, and 32 S-boxes with 64 fields per box. It ensures a strong key-dependent transformation and protects against brute-force attacks, thanks to this long key length. While the performance of BSP-128 is highly promising with regard to core security metrics, experimental findings show that BSP-128 surpasses expectations through computational efficiency. The final design will be submitted for public survey and comparison in academia, resulting in a secure and high throughput candidate tailored for contemporary cryptographic uses.