Comments on "A Novel Compression and Encryption Scheme Using Variable Model Arithmetic Coding and Coupled Chaotic System

Recently, Bose and Pathak proposed a joint compression-encryption scheme by incorporating an adaptive arithmetic coder with a coupled chaotic system . In this comment, we first show that the scheme proposed by Bose and Pathak is not decodable. It is due to the fact that the current symbol to be encoded is swapped with a randomly selected symbol in the model prior to encoding it, making it impossible for the decoder to mirror the encoder´s operations. We then suggest a natural solution to solve the undecodability problem by using the last encoded symbol to swap. Unfortunately, it can be shown that this modified scheme is vulnerable against a chosen-plaintext attack.