bFLEX-γ: A Lightweight Block Cipher Utilizing Key Cross Approach via Probability Density Function

Most of the symmetric lightweight cryptosystems keep their block length fixed throughout the entire encryption making the cryptanalysis straightforward. It is of utmost importance to change the block size during the encryption process to introduce complexity in the cryptanalysis process. Therefore, a novel block cipher-based cryptosystem bFLEX-gamma has been proposed in which the bit length of the ciphertext gets changed in the intermediate rounds. The key scheduling of the proposed cryptosystem takes place with the random diffusion of the auxiliary vector anticipated by a key crossing technique and linear shift feedback register (LFSR). Simulation results indicate that the proposed bFLEX-gamma gives a satisfying level of security and robustness against linear cryptanalysis, differential cryptanalysis, eXtended Sparse Linearization (XSL) attacks and regression analysis attacks. The proposed cryptosystem is also validated by 0-1 balance factor of 0.020925% and a kurtosis of 2.55, showing platykurtic in nature. All the statistical features and efficiency confirm that bFLEX-gamma is very suitable for lightweight applications demanding data confidentiality.