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Yayın Comment on "Encryption and decryption of images with chaotic map lattices" [Chaos 16, 033118 (2006)](American Institute of Physics Inc., 2008-09) Solak, Ercan; Çokal, CahitIn this paper, we comment on the chaotic encryption algorithm proposed by A. N. Pisarchik et al. [Chaos 16, 033118 (2006)]. We demonstrate that the algorithm is not invertible. We suggest simple modifications that can remedy some of the problems we identified.Yayın Security of chaotic cryptosystems(Işık Üniversitesi, 2008) Çokal, Cahit; Solak, Ercan; Işık Üniversitesi, Fen Bilimleri Enstitüsü, Bilgisayar Mühendisliği Yüksek Lisans ProgramıIn this thesis, we tried to show the weaknesses of chaotic cryptosystems. We break four chaos-based cryptosystems and proved our attacks. In our first cryptanalysis, we broke a cryptosystem based on two dimensional chaotic maps. We first reveal a portion of the secret key using a chosen-ciphertext attack. After revealing this portion, we used it to reveal the other portions of the secret key. We developed three types of attack using algebraic properties of the permutations in revealing the rest. We finally published two papers for this break. In our second cryptanalysis, we broke a cryptosystem that encrypts and decrypts images with chaotic map lattices. Here we first show that the encryption algorithm is not invertible for some cases. We showed why these cases not work, and gave some suggestions to improve the algorithm. However, we showed that the algorithm still is not invertible due to finite precision arithmetic. Furthermore, we gave some suggestions to develop the algorithm. At the end of our work, we gave a break for the modified algorithm. Finally, we published a comment for the wrong cases. In our third cryptanalysis, we broke a chaos-based image encryption algorithm, which uses a two-dimensional chaotic map to shuffle the image pixels and a threedimensional chaotic map to change the gray levels of the pixels. We used a chosenplaintext attack and a known-plaintext attack to break the algorithm. Applying either our chosen-plaintext attack or our known-plaintext attack the cryptosystem yields the secret parameters successfully. We published a paper for this break. Our final cryptanalysis was on an image encryption algorithm based on twodimensional chaotic maps. We showed that the chaotic map can be revealed using a chosen-ciphertext attack. The attack does not depend on which type of map is used. The attack uses some algebraic properties of permutations and graphs.
