By Matthew Gu (Guest Contributor)

The nuclear capabilities of the Soviet Union and the United States during the Cold War were no small matter. A single attack could, in theory, escalate all the way to a devastating nuclear war; millions, if not billions could die. Therefore, secrecy was of the utmost importance. There was a great need for secure channels of communication on both sides of the Iron Curtain. The Russian military needed encryption rivaling Enigma, the fiendishly difficult cipher machine used by the Germans in WWII. But Enigma had been broken by Allied cryptanalysts by the end of WWII. The more secure successor, the German Lorenz cipher machines, had been broken as well by the secret British Colossus computers. A new, stronger encryption was needed.

Enter Fialka. Used primarily through the 1960’s and 1970’s, the machine was used by the Russian military to communicate with other countries in the Soviet Union and Warsaw Pact. Not much is known about Fialka, as it was declassified quite recently in 2005. Translated as Russian for “purple,” Fialka operated on a very similar basis as the previous Enigma machines. Encryption was through an electromechanical process that sent a current through a set of rotors connected by electrical contacts with internal wirings to scramble each letter. The wirings essentially created a particular substitution cipher alphabet, the encrypted output, to correspond with a plaintext alphabet, or unencrypted input. (Singh, 1999)

Traditional ciphers have a single “cipher letter” assigned to every plaintext letter, creating a different “output alphabet”, or cipher alphabet. Ciphers like the Enigma took it a step further. The Enigma was so difficult to crack because after each letter was entered, the first rotor would advance to the next rotation and give a completely new cipher alphabet. Further encryption could be created by changing the initial rotor positions and arrangements. However, Enigma only had three rotors, and the British bombe computers developed to find those initial rotor settings were soon capable of deciphering intercepted plaintext within a day. (Singh, 1999)

While Enigma had three rotors (four towards the end of the war), Fialka had ten. Furthermore, each rotor had 30 electrical contacts corresponding to 30 Russian characters. While the design of the machine meant it was more difficult to rearrange the rotors like the Enigma, the sheer number of possible rotor settings compensated for that shortcoming. The internal wires within each rotor were also removable, and could be repositioned in any of the thirty rotations within the external ring on a rotor as well as backwards, creating 60 possible arrangements. Further security is created by a complex drive mechanism that caused alternate rotors to be turned in opposite directions. (Hamer, Perera, 2005)

Aside from being much more secure than Enigma, Fialka was also easier to use. German Enigma machines frequently required two operators since the letters were output by way of a light board on top of the machine. While one operator typed in plain text or a received cipher message, the other would have to record the light board signals. This was slow enough that touch-typing was impossible.

Fialka, on the other hand, used a printer with a paper tape output to facilitate quick encryption and decryption of messages by a single operator. Additionally, the machine both printed and accepted paper punch cards. One advantage that Enigma did have over Fialka, though, was that it was almost half the weight of Fialka. Being made with a primarily metal body and components, Fialka was almost 50 pounds! Granted, the Cold War was not a traditional war with much fighting and battlefield maneuvering so there was not really a need for portability. (Hamer, Perera, 2005)

Cracking Fialka

Cryptanalysis of Fialka was difficult, but not impossible. The ten rotors with 30 character positions each and two ways to slot in the rotor (forwards and backwards) gave a massive number of starting configurations, over 604 quadrillion possibilities! Adding in the later upgrade of a rotor with changeable wirings gives another 403 heptillion, or 403 trillion trillion possibilities. Like in Enigma, the rotors themselves can be rearranged in another ten factorial, or 3.6 million ways. Finally, a day key can be inputted on a punch card that swaps certain letters, functioning like the Enigma’s plugboard. Multiplying, we see that even without the day key, the number of possible starting configurations number in at 8.7 followed by fifty zeroes (Reuvers, Simons, 2009).

Analyzing some operator habits and captured information such as daily key books could reduce this number significantly. For example, while rotating the rotors was simple, taking all ten out and rearranging them was quite a hassle as the design did not allow for individual rotor removal. And as always, with rotor machines the issue of key distribution from higher command to the operators was a constant issue.

Even more helpful was the introduction of more advanced programmable digital computers. Compared to the British bombes in WWII used to find rotor settings for Enigma, digital computers were not physically limited by machinery and could be programmed for multiple tasks. Also, electronic circuitry operated much faster with less possibility of breakdown than a strictly mechanical solution. Indeed, as the NSA developed more powerful computers, the US was able to decrypt Fialka traffic with relative ease by the 1970’s (Courtois, 2012).

The increasing complexity of electromechanical ciphers using rotor technology had its limitations. Israel captured a machine during the 6 Day War in 1967, and the NSA built a computer to decrypt Fialka traffic fairly easily (Courtois, 2012). The fact was, rotor ciphers became so frequently used that finding a method of cryptanalysis was hardly new territory. Rotor machines and electromechanical ciphers had already begun to reach the end of their usefulness when digital computing delivered the deathblow.

The Next Wave in Cryptography

New encryption methods were needed, both for renewed security as well as to keep up with the Digital Age. Claude Shannon, an American mathematician, wrote an essay on “A Mathematical Theory of Communication” (Shannon, 1948). This was a major spark that set off the development of mathematical cryptography using functions and algorithms instead of cipher alphabets. This led to encryption standards such as the Data Encryption Standard and RSA encryption that much of our online communication today is based on.

Fialka was undoubtedly an impressive piece of technology. It was perhaps one of the most advanced rotor machines ever built. However, it suffered from poor timing. Rotor machines had been around for a while. They were initially secure, but the more time passed, the more familiar cryptanalysts became with decryption techniques. Computers merely hastened that end. Fialka was the capstone of the era of electromechanical ciphers, but it was also a harbinger of times to come. When the world experienced the digital revolution, cryptography was carried along for the ride, and Fialka was left behind.

This post is part of a series of essays on the history of cryptography produced by students at Vanderbilt University in honor of the release of The Imitation Game, a major motion picture about the life of British codebreaker and mathematician Alan Turing. The students wrote these essays for an assignment in a first-year writing seminar taught by mathematics instructor Derek Bruff. For more information on the cryptography seminar, see the course blog. And for more information on The Imitation Game, which opens in the US on November 28, 2014, see the film’s website.

Sources:

Courtois, N. (2012, December 28). Cryptanalysis of GOST. 29th Chaos Communications Congress. Lecture conducted from CCH Congress Center, Hamburg, Germany.

Hamer, D. & Perera, T., (2005, January 1). Russian Fialka Cold War era Cipher Machines. Retrieved October 13, 2014, from http://w1tp.com/enigma/mfialka.htm

Reuvers, P., & Simons, M. (2009, October 24). Fialka. Retrieved October 28, 2014.

Shannon, C. (1948). A Mathematical Theory of Communication. ACM SIGMOBILE Mobile Computing and Communications Review, 3-3.

Singh, S. (1999). The code book: The evolution of secrecy from Mary, Queen of Scots, to quantum cryptography. New York: Doubleday.