Enigma machine
The Enigma machine is a cipher device developed and used in the early- to mid-20th century to protect commercial, diplomatic, and military communication. It was employed extensively by Nazi Germany during World War II, in all branches of the German military. The Enigma machine was considered so secure that it was used to encipher the most top-secret messages.
The Enigma has an electromechanical rotor mechanism that scrambles the 26 letters of the alphabet. In typical use, one person enters text on the Enigma's keyboard and another person writes down which of the 26 lights above the keyboard illuminated at each key press. If plaintext is entered, the illuminated letters are the ciphertext. Entering ciphertext transforms it back into readable plaintext. The rotor mechanism changes the electrical connections between the keys and the lights with each keypress. In essence, the rotor's motion means every letter is encrypted with a different cryptographic key, making it highly resistant to conventional cryptographic attacks based on patterns the keys leave in the resulting cyphertext.
For the system to be bidirectional, the receiving station would have to know and use the exact settings employed by the transmitting station to decrypt a message. This consisted of a series of initial settings that were generally changed daily, based on secret key lists distributed in advance. Due to the large number of messages transmitted every day, this could allow the system to be attacked if enough messages were intercepted. To complicate this, operators would choose some other random settings of the rotors, say "GTZ", and then use the day settings to encode that key and send it. They would then change the rotors to those chosen settings and send the rest of the message. That meant that only those three letters were set to the day code, although normally typed twice for a total of six characters. This made it seemingly impossible to gather enough cyphertext to attack it.
Despite the seeming difficulty in decrypting its messages, Enigma contained a number of design issues that left patterns in the cyphertext. Poland first cracked the machine as early as December 1932 and was able to read messages prior to and into the war. Poland's sharing of their achievements enabled the Allies to exploit Enigma-enciphered messages as a major source of intelligence. Although Nazi Germany introduced a series of improvements to the Enigma over the years that hampered decryption efforts, cryptanalysis of the Enigma continued throughout the war. Many commentators say the flow of Ultra communications intelligence from the decrypting of Enigma, Lorenz, and other ciphers shortened the war substantially and may even have altered its outcome.
History
The Enigma machine was invented by German engineer Arthur Scherbius at the end of World War I. The German firm Scherbius & Ritter, co-founded by Scherbius, patented ideas for a cipher machine in 1918 and began marketing the finished product under the brand name Enigma in 1923, initially targeted at commercial markets. Early models were used commercially from the early 1920s, and adopted by military and government services of several countries, most notably Nazi Germany before and during World War II.Several Enigma models were produced, but the German military models, having a plugboard, were the most complex. Japanese and Italian models were also in use. With its adoption by the German Navy in 1926 and the German Army and Air Force soon after, the name Enigma became widely known in military circles. Pre-war German military planning emphasised fast, mobile forces and tactics, later known as blitzkrieg, which depended on radio communication for command and coordination. Since adversaries would likely intercept radio signals, messages had to be protected with secure encipherment. Compact and easily portable, the Enigma machine filled that need.
Breaking Enigma
was a German who spied for the French, obtaining access to German cipher materials that included the daily keys used in September and October 1932. Those keys included the plugboard settings. The French passed the material to Poland. Around December 1932, Marian Rejewski, a Polish mathematician and cryptologist at the Polish Cipher Bureau, used the theory of permutations, and flaws in the German military-message encipherment procedures, to break message keys of the plugboard Enigma machine. Rejewski used the French supplied material and the message traffic that took place in September and October to solve for the unknown rotor wiring. Consequently, the Polish mathematicians were able to build their own Enigma machines, dubbed "Enigma doubles". Rejewski was aided by fellow mathematician-cryptologists Jerzy Różycki and Henryk Zygalski, both of whom had been recruited with Rejewski from Poznań University, which had been selected for its students' knowledge of the German language, since that area was held by Germany prior to World War I. The Polish Cipher Bureau developed techniques to defeat the plugboard and find all components of the daily key, which enabled the Cipher Bureau to read German Enigma messages starting from January 1933.Over time, the German cryptographic procedures improved, and the Cipher Bureau developed techniques and designed mechanical devices to continue reading Enigma traffic. As part of that effort, the Poles exploited quirks of the rotors, compiled catalogues, built a cyclometer to help make a catalogue with 100,000 entries, invented and produced Zygalski sheets, and built the electromechanical cryptologic bomba to search for rotor settings. In 1938 the Poles had six bomby, but when that year the Germans added two more rotors, ten times as many bomby would have been needed to read the traffic.
On 26 and 27 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, including Zygalski sheets and the cryptologic bomb, and promised each delegation a Polish-reconstructed Enigma.
In September 1939, British Military Mission 4, which included Colin Gubbins and Vera Atkins, went to Poland, intending to evacuate cipher-breakers Marian Rejewski, Jerzy Różycki, and Henryk Zygalski from the country. The cryptologists, however, had been evacuated by their own superiors into Romania, at the time a Polish-allied country. On the way, for security reasons, the Polish Cipher Bureau personnel had deliberately destroyed their records and equipment. From Romania they travelled on to France, where they resumed their cryptological work, collaborating with the British, who began work on decrypting German Enigma messages, using the Polish equipment and techniques.
Among those who joined the cryptanalytic effort in France was a team of seven Spanish cryptographers, known as "Equipo D", led by Antonio Camazón, former head of the cipher service of the Spanish Republican Army during the Spanish Civil War. After the fall of the Republic in 1939, Camazón and his colleagues sought refuge in France and were recruited by French intelligence officer Gustave Bertrand. They were assigned to the PC Bruno centre near Paris, where they worked alongside Polish cryptanalysts analysing Enigma-encrypted traffic and contributing to the adaptation of Polish decryption methods.
During the Norwegian campaign, three intact Enigma cipher machines belonging to the German Army and Air Force were captured. Starting on 17 May 1940, and were put into operation at the British intelligence centre at Bletchley Park.
Following the German invasion of France in June 1940, the Spanish team relocated first to the Cadix centre in the Vichy-controlled zone and later to Algiers, continuing their work with the Western Allies. Their tasks included manual decryption, rotor setting reconstruction, and message traffic analysis. Though their contribution remained largely unknown for decades, recent historical research and documentaries have highlighted their role in the broader Allied effort to break Enigma.
Gordon Welchman, who became head of Hut 6 at Bletchley Park, wrote: "Hut 6 Ultra would never have got off the ground if we had not learned from the Poles, in the nick of time, the details both of the German military version of the commercial Enigma machine, and of the operating procedures that were in use." The Polish transfer of theory and technology at Pyry formed the crucial basis for the subsequent World War II British Enigma-decryption effort at Bletchley Park, where Welchman worked.
During the war, British cryptologists decrypted a vast number of messages enciphered on Enigma. The intelligence gleaned from this source, codenamed "Ultra" by the British, was a substantial aid to the Allied war effort.
Though Enigma had some cryptographic weaknesses, in practice it was German procedural flaws, operator mistakes, failure to systematically introduce changes in encipherment procedures, and Allied capture of key tables and hardware that, during the war, enabled Allied cryptologists to succeed.
The Abwehr used different versions of Enigma machines. 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 8 December 1941 by Dilly Knox. Agents sent messages to the Abwehr in a simple code which was then sent on using an Enigma machine. The simple codes were broken and helped break the daily Enigma cipher. This breaking of the code enabled the Double-Cross System to operate.
From October 1944, the German Abwehr used the Schlüsselgerät 41 in limited quantities.