A Closer Look at Enigma Machines and their Code

Historians credit the “breaking” of the German Enigma code by British agents during World War II for having shortened the war by nearly two years. The Enigma Machine and the ability it gave to Nazi leaders to communicate in relative secret for at least a portion of the war has been the subject of much historical discussion, as well as formed the plot for several spy movies in the 1970s and 1980s after the British government released information about the machines in the early 1970s nearly 30 years after the war ended. While the Enigma Machine was initially created in 1923 by Arthur Scherbius, a German entrepreneur and engineer seeking to provide business owners with a secure form of communication, the machine quickly became the tool of choice for military operations. Before its invention, military operatives had little choice but to rely on paper and pencil encryption techniques that often led to security breaches. During World War I and II, alliances spread across continents required a more uniform and stable form of secret communication. By 1924, German military units were using the Enigma in an effort to protect messages from enemies.

How the Enigma Works

The enigma machine enciphered and deciphered messages sent between German military units through the combined simultaneous use of a 26-letter exterior keyboard, a corresponding interior lampboard with 26 windows lit from below by a series of bulbs powered by a 4.5 volt battery, a scrambler unit with two fixed wheels each containing 26 contact point, and three non-fixed wheels each also bearing 26 contact points to represent letters of the alphabet. The fixed wheels were located on the far right and far left sides of the enigma machine. The fixed wheel on the right side of the enigma machine began the process of deciphering messages as various keys outlined in encrypted written messages were pressed on the exterior keyboard that lit up the specifically connected windows of the lamp board. As the right fixed wheel rotated based on the input from the keyboard, its movement then triggered action from the three inner wheels to then move to and select the appropriate corresponding letters of the alphabet as well as the numbers 1 through 26 for the contents of the message to be delivered. By beginning on the left fixed wheel and entering keystrokes on the exterior keyboard, military members could then encipher messages to be sent to other units in the field or back at headquarters. The middle wheels would respond in like manner as when deciphering in that their movement keyed specific letters and numbers. The three center wheels were selected for use from a series of five wheels that equipped each enigma machine. This selection was based on monthly orders from military headquarters based on what encryption codes were being used. With five sets of wheels, this meant German authorities had 60 different wheel order combinations to select from for encrypting purposes.

Breaking the Code

Allied forces owe the breaking of the German enigma machine codes relatively early in World War II to the work of Polish cryptanalysts and mathematicians who made the most of information given them by a French cryptographer, Gustave Bertrand. By the start of the 1930s, both the Polish and French governments began to view German activities as threats to their autonomy. The Polish began to secretly monitor much of Germany’s military radio transmission and had identified the German use of an enigma machine for encryption, but were unable to break the code until Bertrand provided key information he had acquired from a German traitor named Hans-Thilo Schmidt. By 1932, a team of three young Polish mathematicians were already experiencing some success in tackling the mathematical applications of the exterior side of the enigma machine and its input of codes. They were however unable to use mathematical equations to uncover the inner workings of the enigma machine and its series of cues. This is where the information obtained by Bertrand that included original operating instructions and two sheets of the monthly middle wheel selections provided the Polish team with what was needed to break the German code. By having access to which wheel selections were in use for two specific months and by reviewing what radio traffic had been captured, the Polish team was able to use knowledge of the corresponding keystrokes for each wheel to discover the code encryption

From this information, the Polish then devised their own version of the German enigma machine that was called a Cyclometer. The Polish team then used it to run a series of keystroke characteristics that was later developed in to a reference catalog. Unfortunately for the Polish, the Germans changed their process used for encryption in the fall of 1938 in that they no longer allowed enigma operators to use the same standard wheels for a 24-hour period. Still, the Polish had more than basic operating information and its team of crypto analysts continued tackling the German code. They realized that the Germans used the same letter in the first and fourth, second and fifth, and third and sixth positions of encryption. This then gave them the basis for creating a series of data sheets that could be run through mathematical models to being deciphering the latest round of German code. The Polish kept their work and its success a secret until 1939 when it became obvious that Germany’s forces would invade Poland and most likely take over the nation. The Polish information was passed to French agents and later on to British agents.

Additional Resources

  • How Enigma Works: This article written by Alan Stripp of NOVA gives detailed information on the inner technical workings of the German Enigma Machine as well as links to modern day cryptology applications.
  • The Breaking of Enigma by the Polish Mathematicians: This informational essay outlining the process by which the German Enigma codes were broken was written by Tony Sale, the original curator of the Bletchley Park Museum located on the same site where British agents decoded during World War II and where the Government Code and Cypher School as well as Station X, a radio transmission intercepting station, was located.
  • War of Secrets: Cryptology in WW II: This fact sheet posted in 2011 on the museum’s website gives a brief overview detailing how the work of Polish cryptanalysts prior to World War II aided the Allied forces in deciphering German military transmissions.
  • World War 2 Code Breaking: This website contains a written synopsis of the program aired on the History Channel as well as video interviews of code makers and code breakers on both sides of the World War II conflict.
  • Cipher Machines and Cryptology: Technical Details of the Enigma Machine: This website details the technical aspects of the Enigma Machine from its wiring diagram, rotors, rotor wiring tables, rotor encryption process, plugboard, and accessories as well as a link to a demonstration Enigma simulator.
  • Bletchley Park National Codes Center: This is the official website for the estate that housed the workings of British code breakers during World War II and the United Kingdom’s Government Code and Cypher School at which the National Codes Centre is now housed.
  • Internet On-Line ENIGMA Museum: This website maintained by Professor Tom Perera, PhD, professor emeritus of psychology from Montclair State University, provides an overview of the Enigma Machine as well as access to original movie footage of Enigma Machines in action and a video reenactment of the workings of an Enigma Machine.
  • The Enigma Machine: Online access to original photos of German Enigma Machines once only available at the Electronic Museum at the University of Hamburg in Germany, as well as a virtual tour of Bletchley Park and a virtual lecture from former code breakers and software simulations of Enigma Machines at work is available at this website.
  • Crypto Machines: Enigma: This website maintained by Jerry Proc, who is a radio systems volunteer at the national historic site in Hamilton, Ontario, Canada where the HMCS (Her Majesty’s Court Service) Haida, a destroyer that sank more tonnage than any other Canadian vessel in World War II, is now dry-docked, has numerous photos of Enigma Machines and various parts providing detailed information about each photo.
  • History: Enigma: This website featuring the journalistic work of the British radio and television network features highlights and excerpts from programs regarding the Enigma Machines.
  • Cipher Machines: The Technology and History of the Enigma Cipher Machine: This website details the early history of the Enigma Machine, presents its usage by Nazi Germany operatives, discusses how its code was broken, and then explains how the British World War II efforts in mastering the techniques of deciphering later led to the birth of modern day computing.
  • About Enigma and Its Decryption: This privately-maintained website provides an in-depth look at the history of the Enigma Machine including information about its 1923 invention by a German entrepreneur who initially created the machine as a method for secure business communication.
  • Breaking the German Code – the Enigma Machine: This website, which is a service of the Polish Academic Information Center at the University at Buffalo, provides an extensive listing of links to other websites and articles regarding Enigma Machines and their role in World War II.
  • Games: Enigma Code: As part of an online outreach to engage children to learn more about the operations of the CIA, this page allows children or users of any age to try their hand at deciphering an Enigma Machine styled message.
  • Cryptography Defined/Brief History: This student-written essay explains the role of mathematics in the encryption and decryption of data.