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In this article we propose a new fragile watermarking algorithm that provides the means to verify the integrity of JPEG images. We begin by presenting the cryptanalysis of CWSA (Chaotic Watermarking Scheme for the Authentication of JPEG Images), an existing fragile watermarking algorithm. We analyse its weaknesses and we propose a new version that is resistant to those attacks, faster and less perceptible. The proposed algorithm uses the JPEG quantized DCT coefficients and embeds the watermark information in their LSB. It uses robust chaotic generators for the generation of dynamic keys and watermarking information. One of the applications of the proposed algorithm is verifying data integrity for images transferred over the Internet.

In this paper, we propose a novel pseudo chaotic random number generator based on three weakly-coupled discrete Skew tent maps. Its implementation was performed with C language and finite precision N=32, including a chaotic multiplexing technique. We show that our approach permits to avoid dynamic degradation caused by finite precision in one hand, and to allow emergence from chaos toward randomness in the other hand. As a consequence, the proposed generator turns out to be secure against famous cryptographic and statistical attacks. Several statistical tests such as correlation, histogram, chi2 and NIST have been applied on the generated sequences. They confirm the robustness of this chaotic generator.