With the rapid development of digital signal processing tools, image contents can be easily manipulated or maliciously tampered with. Fragile watermarking has been largely used for content authentication purposes. This article presents a new proposal for image fragile watermarking algorithms for tamper detection and image recovery. The watermarked bits are obtained from the parity bits of an error-correcting code whose message is formed from a binary chaotic sequence (generated from a secret key known to all legitimate users) and from bits of the original image. Part of the codeword (the chaotic bits) is perfectly known to these users during the extraction phase, adding security and robustness to the watermarking method. The watermarked bits are inserted at specific sub-bands of the discrete wavelet transform of the original image and are used as authentication bits for the tamper detection process. The imperceptibility, detection, and recovery of this algorithm are tested for various common attacks over digital images. The proposed algorithm is analyzed for both grayscale and colored images. Comparison results reveal that the proposed technique performs better than some existing methods.
This article introduces new symmetric key architectures based on a randomized version of the Simplified Advanced Encryption Standard (SAES). It is proposed a new technique to randomize the S-boxes of the original SAES employing chaotic sequences. Then, we study the linear criptanalysis of the proposed schemes. It is shown that, with the introduction of chaotic sequences, the adversary needs a larger number of pairs of plaintext and ciphertext to discover the bits of the key compared to the required by the SAES. Given these results, it is possible to evaluate the improvement of the proposed technique against linear cryptanalysis as compared to the original AES algorithm.
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