Chaos-Based Key Stream Generator
Based on Multiple Maps Combinations and its Application to Images Encryption

Abstract: : In recent years, growing number of cryptosystems based on chaos have been proposed. However, most of them encounter some problems such as: low level of security and small key space. The key stream generator is the key design issue of an encryption system. It directly determines security and efficiency, but most of the proposed key streams are binary valued, and suffer from short period and limited key space. In this paper, we propose an n-ary key stream generator, based on hierarchical combination of three chaotic maps. We demonstrate that the produced key streams have good statistical properties, such as uniform distribution, δ-like auto-correlation function, near-zero cross-correlation and very height sensitivity to initial conditions, under precision restricted condition. An image cryptosystem is constructed using the proposed approach and proven to be enough secure to resist various attacks. Complexity is analysed and an effective acceleration of chaos-based image cryptosystems is shown to be achievable.

Keywords: Chaotic maps, images cryptography, key stream generation, security.

Received December 1, 2008; accepted January 27, 2009