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The dynamical behavior of cellular automata (CA) transition rules are objects of study for different knowledge fields. This paper is about the development of cryptographic methods using CA-like transition rules. We investigate the dynamic behavior of rules that are not able to propagate a perturbation inserted in the initial lattice considering variations of the regular connection structure of CAs that are akin to the small-word network construction process. Extensive experimental results indicate that such modifications in the CA connection structure will produce large changes in the dynamic behavior of the evaluated rules, suggesting that it is possible to increase considerably the space of possible cryptographic keys to methods based on CA rules, provided a different topological construct for the CA lattice is considered. C 2015 Wiley Periodicals, Inc.

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The dynamical system described herein uses a hybrid cellular automata (CA) mechanism to attain reversibility, and this approach is adapted to create a novel block cipher algorithm called HCA. CA are widely used for modeling complex systems and employ an inherently parallel model. Therefore, applications derived from CA have a tendency to fit very well in the current computational paradigm where scalability and multi-threading potential are quite desirable characteristics. HCA model has recently received a patent by the Brazilian agency INPI. Several evaluations and analyses performed on the model are presented here, such as theoretical discussions related to its reversibility and an analysis based on graph theory, which reduces HCA security to the well-known Hamiltonian cycle problem that belongs to the NP-complete class. Finally, the cryptographic robustness of HCA is empirically evaluated through several tests, including avalanche property compliance and the NIST randomness suite.Keywords cellular automata • reversibility • cryptography • block cipher

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