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CASTREAM: A High-speed, Secure Stream Cipher Suitable for Both Hardware and Software
Sourav Das and Dipanwita Roychowdhury

A new Cellular Automata based stream cipher is presented which is suitable for both hardware and software. It has a non-linear combiner where two non-linear blocks along with a linear block are linearly combined to produce the key-streams. Unlike Non-linear Feedback Shift Register (NFSR) based non-linear combiners, it combines 128- bit blocks using parallel evolution of Cellular Automata (CA) and small CA based S-boxes. The usage of CA prevents the correlation attack and two layers of re-usable small S-boxes prevent the algebraic attacks. The stream cipher takes 128 bits Key and 128 bits of Initial Vector (IV). Theoretically, the cipher operates with an encryption speed of nearly 8 bits per cycle. The initialization process needs 96 cycles which is much faster than Grain and Trivium. This stream cipher is extensible in terms of Key size and provides configurable security and vendor specific implementation option. On implementation, the presented cipher receives higher throughput than the existing standards. The security analysis of the cipher is performed and presented in this paper.

Keywords: Cryptography, stream cipher, cellular automata, S-box.

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