F-FCSR: Design of a New Class of Stream Ciphers

In this paper we present a new class of stream ciphers based on a very simple mechanism. The heart of our method is a Feedback with Carry Shift Registers (FCSR) automaton. This automaton is very similar to the classical LFSR generators, except the fact that it performs operations with carries. Its properties are well mastered: proved period, non-degenerated states, good statistical properties, high non-linearity. The only problem to use such an automaton directly is the fact that the mathematical structure (2-adic fraction) can be retrieved from few bits of its output using an analog of the Berlekamp-Massey algorithm. To mask this structure, we propose to use a filter on the cells of the FCSR automaton. Due to the high non-linearity of this automaton, the best filter is simply a linear filter, that is a XOR on some internal states. We call such a generator a Filtered FCSR (F-FCSR) generator. We propose four versions of our generator: the first uses a static filter with a single o...

• Type: Conference
• Year: 2005
• Where: FSE
• Authors: François Arnault, Thierry P. Berger
• Keywords: Carry Shift Registers, Classical Lfsr Generators, Cryptography, FSE 2005, Stream Ciphers