The word key was also used at Bletchley park to describe the network that used the same Enigma setting sheets. Initially these were recorded using coloured pencils and were given the names red, light blue etc., and later the names of birds such as kestrel. 26 During World War ii the settings for most networks lasted for 24 hours, although towards the end of the war, some were changed more frequently. 27 The sheets had columns specifying, for each day of the month, the rotors to be used and their positions, the ring positions and the plugboard connections. For security, the dates were in reverse chronological order down the page, so that each row could be cut off and destroyed when it was finished with. 28 The top part of an early setting sheet looked something like this 29 Datum Date walzenlage rotors Ringstellung Ring settings Steckerverbindungen Plugboard settings Grundstellung Initial rotor settings 31 i ii ii m hk cn io fy jm lw rao 30 ii u.
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The plugboard connections were reciprocal, so that if A was plugged to n, then N likewise became. It was this property that led mathematician Gordon Welchman at Bletchley park to propose that a diagonal board be introduced into the biography bombe, substantially reducing the number of incorrect rotor settings that the bombes found. 21 The notches in the alphabet rings of rotors I to v were in different positions, which helped cryptanalysts to work out the wheel order by observing when the middle rotor was turned over by the right-hand rotor. 22 There were substantial weaknesses, in both policies and practice, in the way that Enigma was used (see 'operating shortcomings' below). Key setting edit Enigma featured the major operational convenience of being symmetrical (or self-inverse ). This meant that decipherment worked in the same way as encipherment, so that when the ciphertext was typed in, the sequence of lamps that lit yielded the plaintext. Identical setting of the machines at the transmitting and receiving ends was achieved by key setting procedures. These varied from time to time and across different networks. They consisted of setting sheets in a codebook. 23 24 which were distributed to all users of a network, and were changed regularly. The message key was transmitted in an indicator 25 as part of the message preamble.
The 3-rotor scrambler could be set in,576 ways, and the 4-rotor scrambler in 26 summary 17,576 456,976 ways. With six leads on the plugboard, the number of ways that pairs of letters could be interchanged was 100,391,791,500 (100 billion) 16 and with ten leads, it was 150,738,274,937,250 (151 trillion). 17 However, the way that Enigma was used by the germans meant that, if the settings for one day (or whatever period was represented by each row of the setting sheet) were established, the rest of the messages for that network on that day could. 18 The security of Enigma ciphers did have fundamental weaknesses that proved helpful to cryptanalysts. A letter could never be encrypted to itself, a consequence of the reflector. 19 This property was of great help in using cribs —short sections of plaintext thought to be somewhere in the ciphertext—and could be used to eliminate a crib in a particular position. For a possible location, if any letter in the crib matched a letter in the ciphertext at the same position, the location could be ruled out. 20 It was this feature that the British mathematician and logician Alan Turing exploited in designing the British bombe.
Finding the book internal and external settings for one or more messages may be called "solving" - although breaking is often used for this process as well. Security properties edit The various Enigma models provided different levels of security. The presence of a plugboard ( Steckerbrett ) substantially increased the security of the encipherment. Each pair of letters that were connected together by a plugboard lead, were referred to as stecker partners, and the letters that remained unconnected were said to be self-steckered. 14 In general, the unsteckered Enigma was used for commercial and diplomatic traffic and could be broken relatively easily using hand methods, while attacking versions with a plugboard was much more difficult. The British read unsteckered Enigma messages sent during the Spanish civil War, presentation 15 and also some Italian naval traffic enciphered early in World War. The strength of the security of the ciphers that were produced by the Enigma machine was a product of the large numbers associated with the scrambling process. It produced a polyalphabetic substitution cipher with a period (16,900) that was many times the length of the longest message.
Logical structure of the machine (unchanging) The wiring between the keyboard (and lampboard) and the entry plate. The wiring of each rotor. The number and position(s) of turnover notches on the rings of the rotors. The wiring of the reflectors. Internal settings (usually changed less frequently than external settings) The selection of rotors in use and their ordering on the spindle ( Walzenlage or "wheel order. The positions of the alphabet ring in relation to the core of each rotor in use ( Ringstellung or "ring settings. External settings (usually changed more frequently than internal settings) The plugboard connections ( Steckerverbindungen or "stecker values. The rotor positions at the start of enciphering the text of the message. Discovering the logical structure of the machine may be called "breaking" it, a one-off process except when changes or additions were made to the machines.
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In the epithesis above photograph, two pairs of letters have been swapped (aj and SO). During World War ii, ten leads were used, leaving only six letters 'unsteckered'. Later Enigma models included an alphabet ring like a tyre around the core of each rotor. This could be set in any one of 26 positions in relation to the rotor's core. The ring contained one or more notches that engaged with a pawl that advanced the next rotor to the left. 12 Later still, the three rotors for the scrambler were selected from a set of five or, in the case of the german navy, eight rotors. The alphabet rings of rotors vi, vii and viii contained two notches which, someone despite shortening the period of the substitution alphabet, made decryption more difficult.
Most military Enigmas also featured a plugboard (German: Steckerbrett ). This altered the electrical pathway between the keyboard and the entry wheel of the scrambler and, in the opposite direction, between the scrambler and the lampboard. It did this by exchanging letters reciprocally, so that if A was plugged to g then pressing key a would lead to current entering the scrambler at the g position, and if G was pressed the current would enter. The same connections applied for the current on the way out to the lamp panel. To decipher German military Enigma messages, the following information would need to be known.
The left hand side of each rotor made electrical connection with the rotor to its left. The leftmost rotor then made contact with the reflector (German: Umkehrwalze ). The reflector provided a set of thirteen paired connections to return the current back through the scrambler rotors, and eventually to the lampboard where a lamp under a letter was illuminated. 10 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; and similarly with the leftmost slow rotor. There are a huge number of ways that the connections within each scrambler rotor—and between the entry plate and the keyboard or plugboard or lampboard—could be arranged. For the reflector plate there are fewer, but still a large number of options to its possible wirings. 11 Each scrambler rotor could be set to any one of its 26 starting positions (any letter of the alphabet). For the Enigma machines with only three rotors, their sequence in the scrambler—which was known as the wheel order (WO) to Allied cryptanalysts—could be selected from the six that are possible. Possible rotor sequences—also known as Wheel Order (WO) Left Middle right i ii iiii ii iii ii iiii iii ihe plugboard ( Steckerbrett ) was positioned at the front of the machine, below the keys.
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It generated a polyalphabetic substitution cipher, with a period before repetition of the presentation substitution alphabet that was much longer than any message, or set of messages, sent with the same key. A major weakness of the system, however, was that no letter could be enciphered to itself. This meant that some possible solutions could quickly 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 (literally, "no special occurrences"—perhaps better translated as "nothing to report with a section of ciphertext, might produce the following: Exclusion of some positions for the possible plaintext keine besonderen Ereignisse ciphertext u position 1 e position. The red cells represent these crashes. Position 2 is a possibility. Structure edit The mechanism of the Enigma consisted of a keyboard connected to a battery and a current entry plate or wheel (German: Eintrittswalze at the right hand end of the scrambler (usually via a plugboard in the military versions). 9 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.
This constant altering of the electrical pathway produces a very 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. 7 First, there is the identification of the system in use, in this case Enigma; second, breaking the system by establishing exactly how encryption takes place, and third, solving, which involves finding the way that the machine was analysis set up for an individual message,. 8 Today, it is often assumed that an attacker knows how the encipherment process works (see kerckhoffs's principle ) and breaking is often used for solving a key. Enigma machines, however, had so many potential internal wiring states that reconstructing the machine, independent of particular settings, was a very difficult task. The Enigma machines edit main articles: Enigma machine and Enigma rotor details The Enigma machine was used commercially from the early 1920s and was adopted by the militaries and governments of various countries—most famously, nazi germany. A series of three rotors from an Enigma machine scrambler. When loaded in the machine, these rotors connect with the entry plate on the right and the reflector drum on the left. The Enigma rotor cipher machine was potentially an excellent system.
(German air force) and a few heer (German army) messages, as the Kriegsmarine (German navy) 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 eventually 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, regular, rapid reading of U-boat messages resumed. Contents General principles edit main article: Cryptanalysis 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. 6 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 german plugboard-equipped Enigma became, nazi germany 's principal crypto-system. It was guaranteed 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, and the British.
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Cryptanalysis of the Enigma ciphering system enabled the western, allies in, world War ii to read substantial amounts. Morse-coded radio communications of the, axis powers that had been enciphered using, enigma machines. This yielded military intelligence which, along with that from other decrypted Axis radio and teleprinter transmissions, was given the codename. This was considered by western Supreme Allied paper Commander. Eisenhower to have been "decisive" to the Allied victory. 1, the Enigma machines were a family of portable cipher machines with rotor scramblers. 2, good operating procedures, properly enforced, would have made the plugboard Enigma machine unbreakable. 3 4, however, most of the german military forces, secret services and civilian agencies that used Enigma employed poor operating procedures, and it was these poor procedures that allowed the Enigma machines to be reverse-engineered and the ciphers to be read.