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Origins of the Enigma

With the rise in the early 1900's of wireless communication the need for secure communications for both military as civilian use became essential. The search to replace the impractical and time-consuming hand ciphers began. In 1917, the American Edward Hugh Hebern developed a cipher machine with rotating disks, each disk performing a substitution cipher. Hebern's idea was the base for many similar machines, developed in several other countries.

In 1918, Engineer Arthur Scherbius patented a cipher machine using rotors. The German Navy and Foreign Offices were approached, but were not interested. In 1923, the rights for the patents went to Chiffriermaschinen-AG, a firm with Scherbius on the board of directors, that commercialized the machine. In 1927, Scherbius bought the 1919 patent from of a similar machine from the Dutchman Koch, in order to secure his own patent, approved in 1925.

The first cipher machine, Enigma A, came onto the market in 1923. It was a large and heavy machine with an integrated typewriter and weighed about 50 Kg. Soon after the Enigma B was introduced, a very similar machine. The weight and size of these machines made them unattractive for military use. The development of the reflector, an idea of Scherbius' colleague Willi Korn, made it possible to design the compact and much lighter Enigma C. Also, the type writer part was replaced by a lamp panel. In 1927, the Enigma D was introduced and commercialized in several versions with different rotor wirings, and sold across Europe to military and diplomatic services. The Enigma D had three normal rotors and one reflector that could be set in one of the 26 positions.

Several intelligence services succeeded in breaking the civil and military Enigma versions which were all based on the commercial D. The Enigma D had no plugboard, a military feature that would increase security considerably from 1935 onwards. The Italian Navy bought the commercial Enigma D, as did Spain during the Spanish Civil War. The Swiss army used the Enigma K, a slightly modified version of the Enigma D. Japan used the Enigma T, also called Tirpiz Enigma, an adapted Enigma D with modified entry rotor connections. Japan also developed their own version of the T, with horizontally placed rotors. The messages of both models T and K were broken as well. The Railway Enigma, another D clone wich was used by the German Reichsbahn in Eastern Europe, was partially broken from 1941 onwards.

Breaking the code

In 1932 Poland's Biuro Szyfrow (Cipher Bureau) initiated attempts to analyse and break the Enigma messages. Although the chief of this Bureau received copies of codebooks sold by the German spy Hans-Thilo Schmidt, he did not give them to his codebreakers. He thought that keeping this information from them might stimulate their efforts. Marian Rejewski, Henryk Zygalski and Jerzy Rozicki succeeded in breaking the Enigma codes and developed an electro-mechanical machine called the Bomba, to speed up the codebreaking process. Two major security flaws in the German Enigma procedures were the global groundsetting and the twice encodes message-key, a procedure to exclude errors. These flaws opened the door to cryptanalysis. In 1939 the Bureau was no longer able to break the codes due to increased sophistication in the design, new procedures and lack of funds for the code breakers. When Germany invaded Poland, the Polish knowledge and several replica Enigma machines were passed to French and British intelligence.

Bletchley Park

The Government Code and Cipher School (GC&CS) at Bletchley Park initially broke Enigma by hand. In August 1940 they started using their own Bombes, designed by Alan Turing and Gordon Welchman. It was also a rotary electro-mechanical device but it worked on an entirely different principle as Jerewski's Bomba. The Turing Bombe searched for the enigma settings for a given piece of plain and cipher text. When an Enigma message was intercepted, codebreakers had to search for cribs. These cribs were presumed pieces of plain text within the encrypted message. This could be "An Der Oberbefehlshaber", "An Gruppe", "Es Lebe Den Fuhrer" or any other standardized piece of text. Once a crib was located (there were some techniques for that) the associations between the letters of the ciphertext and their plain version were entered in the Bombe. The Bombe, which contains a large number of drums, each replicating the rotors of the Enigma, ran through all possible settings to find the key settings that belong to the given pieces of cipher and plain text. Once these settings were found all messages, encrypted with these setting, could be deciphered.

All information retrieved by cryptanalysis, the breaking of codes, had the codename “Ultra” and played a very important and often decisive role during the war, mainly in the Battle of the Atlantic. All Ultra information was used very carefully, so as to avoid suspicion among the German forces. Special liaison officers, trained to deal with this valuable but delicate knowledge, were placed in Headquarters and other strategic places. Moreover, Ultra was never used unless it could be confirmed by a second source in order to avoid giving the German Command reason to suspect that their communications security might be broken.

The Kriegsmarine

The German Kriegsmarine was very successful in applying their Rudeltaktik or "Wolfpack Tactics" with U-boats. They hunted individually for convoys. If a convoy was spotted, they shadowed it and called other U-boats into battle. Once all U-boats were on the spot, they sank the convoy with a closely co-ordinated attack. This technique was so devastating to the allied supplies that it almost decided the outcome of the war. Communication was the keyword and the U-boats used Enigma to send messages to co-ordinate their attacks. After some initial hard times, Bletchley Park broke the naval codes almost continuously. Decreasing effectiveness of his U-boats made Admiral Donitz suspicious and, although reassured by German intelligence that Enigma was secure, he insisted on improving the Enigma's security. Early in 1942 the famous 4-wheel machine was introduced in the Kriegmarine and the complicated 'Shark' codes caused a big crisis at Bletchley Park. The Kriegmarine referred to the spring of 1942 as the "Happy Times" because the Allied forces were unable to decipher the codes and the U-boats were able to continue sinking ships without much interference. More information is found on Enigma and the U-boat War.

Turning the tide

The codebreakers in Blechtley Park discovered by cryptanalysis that a fourth rotor had entered the battlefield of codes. After ten nerve-wracking months of heavy losses, Bletchley Park succeeded in breaking the 'Shark' codes. One reason for the success was the capturing of codebooks by British Navy on German weather ships, and attacks on U-boats like Kapitanleutenant Heidtmann’s U-559 by HMS Petard. More on the codebooks can be found on the enigma procedures and Kurzsignalen pages . The purpose of these weather ship missions was to break into the Shark message traffic, not to steal Enigma machines, as is often wrongly told or shown in movies (as early as 1939, British Intelligence had already received Enigma replicas from the Biuro Szyfrow). Moreover, new Bombes were developed to deal with the four rotor Enigma, and at the end of '43, another fifty of these Bombes became operational in the US Navy.

The tide of the U-boat war had turned. Except for some brief periods, the entire German communication system was intercepted by a large number of listening stations called Y-stations, and the codes were broken in Bletchley Park, where over 7000 workers were employed at its peak. With the positions of the U-boats known, Allied ships could now avoid the enemy and an active hunt for U-boats was started. The elite weapon of the Kriegsmarine got decimated, resulting in heavy losses among the U-boat crews. An estimated 700 U-boats and 30,000 crewman were lost at sea. The German command related these losses to new detection techniques like the ASDIC sonar system, U-boat detection planes, and destroyers, escorting convoys. They did not suspect cryptanalysis of the Enigma.

All improvements, introduced by the German Forces, were tackled successfully by the codebreakers. The introduction of the rewireable D reflector, with its key changes every ten days, proved to be a big problem to the codebreakers. A widespread use of the D reflector would require five to ten days to break a particular key, which would render tactical information useless. Without the D reflector, keys were broken mostly within 24 hours. Fortunately, logistical problems prevented general use of the D reflector in the German forces. Also, German operators were reluctant to use the D reflector and found it too elaborate to program in tactical situations. Instead, the B reflector remained the default reflector and the D reflector was used only for important messages, on the same machines with the same basic machine settings for rotors and plugboard. However, with the key already broken for these machines with the B reflector, the codebreaker only had to retrieve the unknown wiring of the D reflector, used on the same machines. A work that was performed by hand. The fatal mixed use of B and D reflectors enabled the codebreakers to continue reading the once feared D reflector messages. The Enigma Uhr (clock), used by the Luftwaffe, was another useless effort by the Germans to increase the security of the Enigma. The Uhr was a switch that replaced the plugs of the Enigma and provided 40 different plug wirings. However, the unique design of the Allied Bombes, used to retrieve the key settings of the Enigma, excluded the plugboard wiring. The Enigma Uhr therefore had little or no effect on the codebreaking results.

The Ultra information was kept highly secret during the entire war and played a decisive role, and not only in the Atlantic. Breaking the Wehrmacht and Luftwaffe messages also provided crucial tactical information. The codebreakers exposed the weakness of Field Marshal Rommel's notorious Afrika Korps. The speed and successes of the Afrika Korps created long stretches of poorly defended supply lines. Ultra information provided Field Marshal Montgomery with a vital tactical advantage. In the days before the D-day invasion of Normandie, the Wehrmacht, without realizing it, provided Allied Forces with an enormous quantity of detailed information on the coastal defense, location and strength of all German tank divisions and the movement of troops in France. Experts estimate that breaking Enigma shortened the war by about three years. The number of saved lives cannot be counted. Germany kept on using Enigma during the entire war, without any suspicion.

The heritage of Enigma

After the Second World War, Enigma was the basis for many more sophisticated rotor cipher machines like the Swiss NEMA, the American KL-7 ADONIS and the until recently top secret Russian M-125 FIALKA. Although Enigma was very well designed and offered, for those days, an unbreakable security, the negligent use in the German Armed Forces and the compromised codebook material enabled the codebreakers to turn the best kept secret of the war into a Trojan horse and give the kick-off for cryptographic intelligence. Today, Signal Intelligence is considered to be a most vital part of the modern battle.

All images on this page copyright D Rijmenants

References

Related Links on this site

• Enigma Code Books and Message Procedures
• Technical Details on the Enigma
• Enigma and the U-boat War
• Kurzsignale (Short Signals) on German U-boats
• Break an original M4 message and the story of U-264
• Enigma Cipher Challenge
• Enigma Codebook Tool
• Enigma FAQ page
• Historia de la Maquina de Cifrado Enigma (pdf) This page translated to Spanish by Rafael Padilla

Off-Site Related to Enigma

• Tom Perera's Enigma museum Tom is a collector of Enigmas and other cipher machines. On his site, you can find a huge number of very detailed photographs. He's also the first to publish all details of the famous Russian Fialka M-125, top secret until recently.
• Tom's Enigma In Action video Tom created a very nice video that shows how to set the daily key on the Enigma, change the rotors, ring settings and plugboard connections, and how a message is enciphered. Great way to see the Enigma in action.
• Frode Weierud's Crypto Pages As a member of the Crypto Simulation Group, Frode has composed a large list of sims. Several Enigma models, PURPLE, the SIGBA, Hagelin CD57 and others. The site contains also a lot of historical information and documents. CSG is decoding a large number of original WW2 German messages, some of which are already published on Frode's site.
• Lech Maziakowski's Enigma History On this site, the importance of the Polish effort on breaking the Enigma is well explained.
• Enigma-E, an electronic DIY building kit Paul Reuvers and Marc Simons have developed a great Do-It-Yourself electronic construction kit.
• Enigma simulators for RISC OS platform Site with a range of Enigma simulators for computers with the RISC platform. Paul Reuvers from X-Ample Technology has created a list of Enigma sims, the M3, M4, Luftwaffe en G312 Abwehr Enigma.
• Enigma Simulator for MAC OS Magnificent Enigma simulator, written by Terry Long.
• Jim Oram's Enigma Replica
  Jim decided some years ago to build his own Enigma. Handy man and perfectionist that he is, things got out of control, and he produced a perfect replica of the real thing. Now, even Enigma collectors order spare parts in his shop. Great site!
• The Enigma Machine on Wikipedia Very complete description of Enigma and its history, with lots of secondary links, containing some of my contributions such as the wiring diagram, the accessories, rotor wiring tables and clarification of the double stepping.
• The Enigma School Project A genuine Enigma machine and a code breaking workshop in your school. A project in the UK to get children interested in mathematics by teaching them how Enigma and other encryptions work.
• Tony Sale's Codes & Ciphers Tony is walking computer history. One of the people who helped saving Bletchley Park. He even rebuilt the famous Colossus computer in the Park's museum.
• Bletchley Park, England Official site of the Bletchley Park Thrust. In the Second World War, this was the center of all British code breaking efforts.
• Enigma on the German U-Boats A great site with a huge archive on the German U-boats. There is a very interesting page on the use of Enigma and the efforts on breaking the U-boat Enigma codes
• Enigma and the Bombe The story of breaking enigma and the use of Bombes by Graham Ellsbury.
• Codebreaking and secret weapons in WWII Very complete historical information on the breaking of the Enigma messages.
• NSA's National Cryptologic Museum NSA museum pages with lots of information on intelligence, code breaking and Enigma
• Paper Replika Enigma M4Assemble your own Naval Enigma replica with only a printer, scissors and a bit of glue.
• Daniel Palloks Javascript Enigma's Very nice Javascript versions of the Wehrmacht Enigma, the Abwehr G, the Kriegsmarine M3 and M4.
• Erik Vestergaard's Enigma page A clear as beautiful illistrated page on the breaking of the Enigma machine