An 8-bit precision cipher for fast image encryption

Abstract

Implementing chaos based ciphers usually involves 32-bit floating-point arithmetics that is hardware resources costly. The limitation of the computational precision is hardware imposed and transforms chaotic orbits into limit cycles with short periods, hence alters their randomness. In cryptographic applications, short period dynamics and weak randomness result in security issues. In order to address this concern, we propose an 8-bit precision cipher that can be implemented with low-end microprocessors running 8-bit integer arithmetics. The cipher includes a quantized pseudo-random number generator (QPRNG) based on a 16-dimensional quantized Arnold’s cat map (QACM). We used entropy measure, statistical, sensitivity and key space analyses to evaluate its security level under limited computational precision. Simulation results attest that it is as highly secure as those involving real-number arithmetics, even for only 8-bit precision. We also showed that the period of the proposed QACM can be chosen such that Tx > 1027, which is very large as compared to existing QACM. Such a large period implies a high randomness of the derived QPRNG that is confirmed by statistical NIST tests. Contrary to existing ciphers that include other chaotic systems than the QACM for strengthening the security level, ours is exclusively based on the QACM and is fast, despite the included high-dimensional QACM.