Cryptanalysis of the Enigma
Cryptanalysis of the Enigma ciphering system enabled the western Allies in World War II to read substantial amounts of Morse-coded radio communications of the Axis powers, enciphered using Enigma machines. This yielded military intelligence which, along with that from other decrypted Axis radio and teleprinter transmissions, was given the codename Ultra; this was considered by western Supreme Allied Commander Dwight D. Eisenhower to have been "decisive" to the Allied victory; the Enigma machines were a family of portable cipher machines with rotor scramblers. Good operating procedures, properly enforced, would have made the plugboard Enigma machine unbreakable. However, most of the German military forces, secret services and civilian agencies that used Enigma employed poor operating procedures, it was these poor procedures that allowed the Enigma machines to be reverse-engineered and the ciphers to be read; the German plugboard-equipped Enigma became Nazi Germany's principal crypto-system. It was broken by the Polish General Staff's Cipher Bureau in December 1932, with the aid of French-supplied intelligence material obtained from a German spy.
A month before the outbreak of World War II, at a conference held near Warsaw, the Polish Cipher Bureau shared its Enigma-breaking techniques and technology with the French and British. During the German invasion of Poland, core Polish Cipher Bureau personnel were evacuated, via Romania, to France where they established the PC Bruno signals intelligence station with French facilities support. Successful cooperation among the Poles, the French, the British at Bletchley Park continued until June 1940, when France surrendered to the Germans. From this beginning, the British Government Code and Cypher School at Bletchley Park built up an extensive cryptanalytic capability; the decryption was of Luftwaffe and a few Heer messages, as the Kriegsmarine employed much more secure procedures for using Enigma. Alan Turing, a Cambridge University mathematician and logician, provided much of the original thinking that led to the design of the cryptanalytical bombe machines that were instrumental in breaking the naval Enigma.
However, the Kriegsmarine introduced an Enigma version with a fourth rotor for its U-boats, resulting in a prolonged period when these messages could not be decrypted. With the capture of relevant cipher keys and the use of much faster US Navy bombes, rapid reading of U-boat messages resumed; the Enigma machines produced a polyalphabetic substitution cipher. During World War I, inventors in several countries realized that a purely random key sequence, containing no repetitive pattern, would, in principle, make a polyalphabetic substitution cipher unbreakable; this led to the development of rotor cipher machines which alter each character in the plaintext to produce the ciphertext, by means of a scrambler comprising a set of rotors that alter the electrical path from character to character, between the input device and the output device. This constant altering of the electrical pathway produces a long period before the pattern—the key sequence or substitution alphabet—repeats. Decrypting enciphered messages involves three stages, defined somewhat differently in that era than in modern cryptography.
First, there is the identification of the system in use, in this case Enigma. Today, it is assumed that an attacker knows how the encipherment process works and breaking is used for solving a key. Enigma machines, had so many potential internal wiring states that reconstructing the machine, independent of particular settings, was a difficult task; the Enigma rotor cipher machine was an excellent system. It generated a polyalphabetic substitution cipher, with a period before repetition of the substitution alphabet, much longer than any message, or set of messages, sent with the same key. A major weakness of the system, was that no letter could be enciphered to itself; this meant that some possible solutions could be eliminated because of the same letter appearing in the same place in both the ciphertext and the putative piece of plaintext. Comparing the possible plaintext Keine besonderen Ereignisse, with a section of ciphertext, might produce the following: The mechanism of the Enigma consisted of a keyboard connected to a battery and a current entry plate or wheel, at the right hand end of the scrambler.
This contained a set of 26 contacts that made electrical connection with the set of 26 spring-loaded pins on the right hand rotor. The internal wiring of the core of each rotor provided an electrical pathway from the pins on one side to different connection points on the other; the left hand side of each rotor made electrical connection with the rotor to its left. The leftmost rotor made contact with the reflector; the reflector provided a set of thirteen paired connections to return the current back through the scrambler rotors, to the lampboard where a lamp under a letter was illuminated. Whenever a key on the keyboard was pressed, the stepping motion was actuated, advancing the rightmost rotor one position; because it moved with each key pressed it is sometimes called the fast rotor. When a notch on that rotor engaged with a pawl on the middle rotor, that too moved. There are a huge n
The Enigma machines are a series of electro-mechanical rotor cipher machines developed and used in the early- to mid-20th century to protect commercial and military communication. Enigma was invented by the German engineer Arthur Scherbius at the end of World War I. Early models were used commercially from the early 1920s, adopted by military and government services of several countries, most notably Nazi Germany before and during World War II. Several different Enigma models were produced, but the German military models, having a plugboard, were the most complex. Japanese and Italian models were in use. Around December 1932, Marian Rejewski, a Polish mathematician and cryptanalyst, while working at the Polish Cipher Bureau, used the theory of permutations and flaws in the German military message encipherment procedures to break the message keys of the plugboard Enigma machine. Rejewski achieved this result without knowledge of the wiring of the machine, so the result did not allow the Poles to decrypt actual messages.
The French spy Hans-Thilo Schmidt obtained 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 the Poles, Rejewski used some of that material and the message traffic in September and October to solve for the unknown rotor wiring. The Polish mathematicians were able to build their own Enigma machines, which were called Enigma doubles. Rejewski was aided by cryptanalysts Jerzy Różycki and Henryk Zygalski, both of whom had been recruited with Rejewski from Poznań University; 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 the German Enigma messages starting from January 1933. Over time, the German cryptographic procedures improved, the Cipher Bureau developed techniques and designed mechanical devices to continue reading the 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, made Zygalski sheets and built the electro-mechanical cryptologic bomb to search for rotor settings.
In 1938, the Germans added complexity to the Enigma machines that became too expensive for the Poles to counter. The Poles had six bomby, but when the Germans added two more rotors, ten times as many bomby were needed, the Poles did not have the resources. On 26 and 27 July 1939, in Pyry near Warsaw, the Poles initiated French and British military intelligence representatives into their Enigma-decryption techniques and equipment, including Zygalski sheets and the cryptologic bomb, promised each delegation a Polish-reconstructed Enigma; the demonstration represented a vital basis for the British continuation and effort. 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, Allied capture of key tables and hardware that, during the war, enabled Allied cryptologists to succeed and "turned the tide" in the Allies' favour.
The German firm Scherbius & Ritter, co-founded by Arthur Scherbius, patented ideas for a cipher machine in 1918 and began marketing the finished product under the brand name Enigma in 1923 targeted at commercial markets. With its adoption by the German Navy in 1926 and the German Army and Air Force soon after, the name Enigma became known in military circles; the word enigma is a Latin word, derived from the Ancient Greek word enigma used in English, but not native German. Like other rotor machines, the Enigma machine is a combination of mechanical and electrical subsystems; the mechanical subsystem consists of a keyboard. The mechanical parts act in such a way; when a key is pressed, one or more rotors rotate on the spindle. On the sides of the rotors are a series of electrical contacts that, after rotation, line up with contacts on the other rotors or fixed wiring on either end of the spindle; when the rotors are properly aligned, each key on the keyboard is connected to a unique electrical pathway through the series of contacts and internal wiring.
Current from a battery, flows through the pressed key, into the newly configured set of circuits and back out again lighting one display lamp, which shows the output letter. For example, when encrypting a message starting ANX... the operator would first press the A key, the Z lamp might light, so Z would be the first letter of the ciphertext. The operator would next press N, X in the same fashion, so on. Current flowed from the battery through a depressed bi-directional keyboard switch to the plugboard. Next, it passed through the plug "A" via the entry wheel, through the wiring of the three or four installed rotors, entered the reflector; the reflector returned the current, via an different path, back through the rotors and entry wheel, proceeding through plug "S" connected with a cable to plug "D", another bi-directional switch to light the appropriate lamp. The repeated changes of electrical