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Enigma machine: the story on HearLore | HearLore
Enigma machine
On the 23rd of February 1918, a German engineer named Arthur Scherbius filed a patent for a ciphering machine that used rotating disks to scramble letters, a device that would eventually become the most famous encryption tool of the twentieth century. Scherbius and his partner E. Richard Ritter founded the firm Scherbius & Ritter, but their initial pitch to the German Navy and Foreign Office was met with indifference. It was not until 1923 that the machine, marketed as the Enigma Handelsmaschine, was exhibited at the Congress of the International Postal Union, and even then, it was a heavy, bulky typewriter-like contraption that weighed approximately 26 kilograms and measured 65 by 45 by 38 centimeters. The early commercial models lacked the reflector, a crucial component that would later define the machine's unique self-reciprocal nature, and they required the operator to manually switch between enciphering and deciphering modes. Despite these early flaws, the machine found its way into the hands of commercial users and eventually the military, setting the stage for a cryptographic arms race that would span two decades and influence the outcome of a global war.
Polish Mathematicians Break The Code
In December 1932, a Polish mathematician named Marian Rejewski used the theory of permutations to solve for the unknown rotor wiring of the German military Enigma machine, a feat that seemed impossible to the German cryptographic experts. Rejewski was aided by fellow mathematicians Jerzy Różycki and Henryk Zygalski, who had been recruited from Poznań University, an institution selected for its students' knowledge of the German language since the area had been held by Germany prior to World War I. The breakthrough was made possible by Hans-Thilo Schmidt, a German who spied for the French, obtaining access to German cipher materials that included the daily keys used in September and October 1932. The French passed this material to Poland, allowing Rejewski to build his own Enigma machines, dubbed Enigma doubles, and develop techniques to defeat the plugboard. By January 1933, the Polish Cipher Bureau was reading German Enigma messages, and over time they developed mechanical devices to continue reading traffic, including a cyclometer invented by Rejewski to help make a catalogue with 100,000 entries and Zygalski sheets. In 1938, the Poles had six bomby, but when the Germans added two more rotors, ten times as many bomby would have been needed to read the traffic. On the 26th and the 27th of July 1939, in Pyry, just south of Warsaw, the Poles initiated French and British military intelligence representatives into the Polish Enigma-decryption techniques and equipment, promising each delegation a Polish-reconstructed Enigma. This transfer of theory and technology formed the crucial basis for the subsequent World War II British Enigma-decryption effort at Bletchley Park, where Gordon Welchman later wrote that Hut 6 Ultra would never have got off the ground if they had not learned from the Poles in the nick of time.
When was the Enigma machine patented by Arthur Scherbius?
Arthur Scherbius filed a patent for the Enigma machine on the 23rd of February 1918. This patent described a ciphering machine that used rotating disks to scramble letters.
Who broke the Enigma machine code before World War II?
Polish mathematician Marian Rejewski broke the Enigma code in December 1932 using the theory of permutations. He was assisted by Jerzy Różycki and Henryk Zygalski, and the breakthrough relied on cipher materials obtained from Hans-Thilo Schmidt.
What is the double-stepping flaw in the Enigma machine?
The double-stepping flaw caused rotor two to move again on the subsequent keystroke if the ratchet of rotor three was engaged. This mechanical quirk reduced the machine's period to 16,900 and created predictable patterns that cryptanalysts exploited.
When did the German Navy introduce the four-rotor M4 Enigma machine?
The German Navy introduced the M4 Enigma machine on the 1st of February 1942 for U-boat traffic. This model included an extra rotor known as Beta or Gamma that never stepped but could be manually set to any of 26 positions.
Where are Enigma machines currently displayed?
Enigma machines are displayed in museums such as the Deutsches Museum in Munich, the Deutsches Spionagemuseum in Berlin, and the National Codes Centre at Bletchley Park. Other locations include the Polish Army Museum in Warsaw and the Swedish Army Museum in Stockholm.
How many different settings did the military Enigma machine have?
The military Enigma machine had 158,962,555,217,826,360,000 different settings. This number represents nearly 159 quintillion possibilities derived from choosing three rotors from five, setting 26 positions, and connecting ten pairs of letters on the plugboard.
The Enigma machine contained a subtle design flaw known as double-stepping, which caused the rotors to deviate from odometer-style regular motion and ultimately allowed cryptanalysts to find patterns in the ciphertext. In a three-rotor machine, double-stepping affected rotor two only, meaning that if the ratchet of rotor three was engaged, rotor two would move again on the subsequent keystroke, resulting in two consecutive steps. This mechanical quirk meant that the machine had a period of 26 times 25 times 26, or 16,900, rather than the expected 26 to the power of 3, because of the double-stepping. The stepping mechanism varied slightly from model to model, with the right-hand rotor stepping once with each keystroke, and other rotors stepping less frequently. The position of the turnover notches on each rotor was determined by the letter ring, which could be adjusted in relation to the core containing the interconnections. The first five rotors to be introduced, numbered I through V, contained one notch each, while the additional naval roters VI, VII, and VIII each had two notches. This design feature, intended as a security measure, ultimately allowed the Polish Clock Method and British Banburismus attacks to succeed, as the double-stepping created a predictable pattern that could be exploited by mathematicians who understood the machine's internal mechanics.
The Reflector That Never Stepped
With the exception of models A and B, the last rotor in the Enigma machine came before a reflector, a patented feature unique to Enigma among the period's various rotor machines, which connected outputs of the last rotor in pairs and redirected current back through the rotors by a different route. The reflector ensured that Enigma would be self-reciprocal, meaning that with two identically configured machines, a message could be encrypted on one and decrypted on the other without the need for a bulky mechanism to switch between encryption and decryption modes. However, this design also gave Enigma the property that no letter ever encrypted to itself, a severe cryptological flaw that was subsequently exploited by codebreakers. In Model C, the reflector could be inserted in one of two different positions, and in Model D, it could be set in 26 possible positions, although it did not move during encryption. In the Abwehr Enigma, the reflector stepped during encryption in a manner similar to the other wheels, while in the German Army and Air Force Enigma, the reflector was fixed and did not rotate, with four versions existing from the original version marked A to the rewireable reflector called Umkehrwalze D, nick-named Uncle Dick by the British. The reflector allowed a more compact design, but its fixed nature and the self-reciprocal property created a vulnerability that the Polish and British cryptanalysts used to break the machine's codes.
The Plugboard And The Quintillion Settings
The plugboard, or Steckerbrett, was positioned at the front of the machine below the keys and permitted variable wiring that could be reconfigured by the operator, contributing more cryptographic strength than an extra rotor. When in use during World War II, there were ten connections, and up to 13 steckered pairs might be used at one time, although only 10 were normally used. A cable placed onto the plugboard connected letters in pairs, such as E and Q, and the effect was to swap those letters before and after the main rotor scrambling unit. The mathematical analysis of the Enigma transformation showed that choosing three rotors from a set of five, each of the 3 rotor settings with 26 positions, and the plugboard with ten pairs of letters connected, the military Enigma had 158,962,555,217,826,360,000 different settings, nearly 159 quintillion or about 67 bits. Because of the large number of possibilities, users of Enigma were confident of its security, and it was not then feasible for an adversary to even begin to try a brute-force attack. However, the plugboard also drove Allied cryptanalysts to develop special machines to solve it, as Enigma without a plugboard, known as unsteckered Enigma, could be solved relatively straightforwardly using hand methods. The plugboard's complexity was a double-edged sword, adding immense security but also creating a target for the sophisticated machines and techniques developed by the Polish and British codebreakers.
The Indicator Procedure And Operator Errors
Most of the key to the Enigma machine was kept constant for a set time period, typically a day, but a different initial rotor position was used for each message, a concept similar to an initialisation vector in modern cryptography. The starting position for the rotors was transmitted just before the ciphertext, usually after having been enciphered, and the exact method used was termed the indicator procedure. One of the earliest indicator procedures for the Enigma was cryptographically flawed and allowed Polish cryptanalysts to make the initial breaks into the plugboard Enigma. The procedure had the operator set his machine in accordance with the secret settings that all operators on the net shared, including an initial position for the rotors, say AOH. The operator turned his rotors until AOH was visible through the rotor windows, then chose his own arbitrary starting position for the message he would send, such as EIN, and typed EIN into the machine twice, producing the encrypted indicator, for example XHTLOA. This was then transmitted, at which point the operator would turn the rotors to his message settings, EIN, and then type the plaintext of the message. The message setting was encoded twice, resulting in a relation between first and fourth, second and fifth, and third and sixth character, a serious security flaw that enabled the Polish Cipher Bureau to break into the pre-war Enigma system as early as 1932. During World War II, codebooks were only used each day to set up the rotors, their ring settings and the plugboard, and the new procedure avoided the security flaw of double encoded message settings, but operator sloppiness and design weaknesses in these indicator procedures remained two of the main weaknesses that made cracking Enigma possible.
The Naval Enigma And The Four-Rotor Shark
The German Navy, or Kriegsmarine, used a more complex version of the Enigma machine, designated M4, which was introduced on the 1st of February 1942 for U-boat traffic, and the network was known as Triton, or Shark to the Allies. The extra rotor was fitted in the same space by splitting the reflector into a combination of a thin reflector and a thin fourth rotor, which was one of two types, Beta or Gamma, and never stepped, but could be manually set to any of 26 positions. The Naval version of the Wehrmacht Enigma had always been issued with more rotors than the other services, initially six, then seven, and finally eight, and the additional rotors were marked VI, VII, and VIII, all with different wiring, and had two notches, resulting in more frequent turnover. The Navy codebooks were printed in red, water-soluble ink on pink paper so that they could easily be destroyed if they were endangered or if the vessel was sunk, and the procedures for German Naval Enigma were more elaborate and more secure than those in other services. The Abwehr used different versions of Enigma machines, and in November 1942, during Operation Torch, a machine was captured which had no plugboard and the three rotors had been changed to rotate 11, 15, and 19 times rather than once every 26 letters, plus a plate on the left acted as a fourth rotor. The Abwehr code had been broken on the 8th of December 1941 by Dilly Knox, and agents sent messages to the Abwehr in a simple code which was then sent on using an Enigma machine, enabling the Double-Cross System to operate. From October 1944, the German Abwehr used the Schlüsselgerät 41 in limited quantities, and the four-rotor Naval Enigma remained a significant challenge for Allied cryptanalysts until the end of the war.
The Legacy Of The Enigma Machine
The effort to break the Enigma was not disclosed until 1973, and since then, interest in the Enigma machine has grown, with machines on public display in museums around the world and several in the hands of private collectors and computer history enthusiasts. The Deutsches Museum in Munich has both the three- and four-rotor German military variants, as well as several civilian versions, and the Deutsches Spionagemuseum in Berlin also showcases two military variants. Enigma machines are also exhibited at the National Codes Centre in Bletchley Park, the Government Communications Headquarters, the Science Museum in London, and many other locations, including the Polish Army Museum in Warsaw and the Swedish Army Museum in Stockholm. In 2020, thanks to the support of the Ministry of Culture and National Heritage, a rare Polish Enigma double assembled in France in 1940 became the property of the Polish History Museum. Occasionally, Enigma machines are sold at auction, with prices in recent years ranging from US$40,000 to US$547,500, and replicas are available in various forms, including an exact reconstructed copy of the Naval M4 model. A rare Abwehr Enigma machine, designated G312, was stolen from the Bletchley Park museum on the 1st of April 2000, and in September, a man identifying himself as The Master sent a note demanding £25,000 and threatening to destroy the machine if the ransom was not paid. In November 2000, an antiques dealer named Dennis Yates was arrested after telephoning The Sunday Times to arrange the return of the missing parts, and in October 2001, Yates was sentenced to ten months in prison and served three months. The legacy of the Enigma machine continues to this day, with machines on display in museums and private collections, and the story of its breaking remaining one of the most important cryptographic achievements of the twentieth century.