Cryptanalysis of two chaotic encryption schemes based on circular bit shift and XOR operations

Recently two encryption schemes were proposed by combining circular bit shift and XOR operations, under the control of a pseudorandom bit sequence (PRBS) generated from a chaotic system. This Letter studies the security of these two encryption schemes and reports the following findings: (1) there exist some security defects in both schemes; (2) the underlying chaotic PRBS can be reconstructed as an equivalent key by using only two chosen plaintexts; (3) most elements in the underlying chaotic PRBS can be obtained by a differential known-plaintext attack using only two known plaintexts. Experimental results are given to demonstrate the feasibility of the proposed attack. (C) 2007 Elsevier B.V. All rights reserved.