Cryptanalysis of a random number generator based on continuous‐time chaos

This study presents the algebraic cryptanalysis of a continuous‐time chaotic random number generator (RNG) based on a Zhongtang chaotic system. The chaos‐based RNG provides key values for logic encryption, round key formation and the substitution box (S‐box) generation steps in AES (advanced encryption standard). In this study, an attack method is proposed to exploit the weaknesses of the chaos‐based RNG used in this cryptographic system. By observing a chaotic state variable and knowing the structure of the target RNG, output bit sequence of the target RNG is reproduced by a clone RNG used in master–slave synchronisation scheme. The feasibility of the attack system is confirmed through simulation and numerical results. Through this attack method, the same S‐box parameters and key values can be obtained which can be used for decryption of the proposed encryption algorithm. This study targets a specific continuous‐time chaos‐based RNG and the associated cryptographic system as a case study. However, the cryptanalysis method described in this study is applicable to any continuous‐time or discrete‐time chaos‐based RNGs. Therefore, this study highlights the security vulnerabilities of chaos‐based RNGs and emphasises that deterministic chaos phenomena itself should not be considered as the actual source of randomness.