Key Space and Period of Fialka M-125 Cipher Machine

Abstract

Fialka M-125 (sometimes called the “Russian Enigma”) is an electro-mechanical rotor cipher machine used during the Cold War. The designers of this cipher eliminated the known weaknesses of Enigma. In this article, the authors summarize the main principle of the Fialka algorithm from public sources. Moreover, they introduce a mathematical model of the Fialka cipher, and they analyse the effect of blocking pin settings on the cipher's period.

Keywords:

• cryptanalysis
• Enigma machine
• Fialka
• machine ciphers

Acknowledgements

The authors are grateful to anonymous reviewers for helpful comments and remarks.

Notes

¹It is possible that detailed information about the Enigma's weaknesses was passed on to the Russians [6, 14].

²For complete technical details including the rotor wirings and electronic description, please refer to [14] and corresponding web page http://www.cryptomuseum.com/crypto/fialka/index.htm, which also includes Fialka simulators.

³We denote rotor settings by an ordered n-tuple of pairs (S, k), where S denotes a rotor wiring permutation in zero position and k a rotation offset. The order of pairs in the n-tuple defines the order of rotors in the Fialka machine.

⁴We use the model of a stream cipher, where stream cipher is defined as a cipher with memory (internal state), which is broader than just a more common additive stream cipher (key generator + addition of keystream to plaintext).

⁵At least in former Czechoslovakia.

Additional information

Notes on contributors

Eugen Antal

Eugen Antal was born in 1987, in Slovakia. He studied IT security (M.S., Slovak University of Technology, Bratislava, 2011). Currently, he is a Ph.D student at the Institute of Computer Science and Mathematics at Slovak University of Technology. As a researcher, he specialises on modern cryptanalysis of classical ciphers. Primarily, he is investigating unsolved homophonic ciphers (Zodiac killer ciphers), rotor cipher machines (Fialka M-125) and historical manuscripts (Rohonc codex). His interest in classical ciphers is motivated by the famous unsolved Zodiac killer's Z340 cipher.

Pavol Zajac

Pavol Zajac is an Associate Professor at the Institute of Computer Science and Mathematics at Slovak University of Technology. He got his Ph.D in applied mathematics in 2008. He is currently working on problems of algebraic cryptanalysis and general cryptology research.