In the History of cryptography, ECM Mark II was an electromechanical machine of coding with rotors used by the the United States of America at the time of the Second world war until the years 1950. This apparatus was also known under name SIGABA or Converter M-134 by the army, or CSP-889 by the US Navy. For this one, a modified version was named CSP-2900 .

As much of machines of this time, it used an electromechanical system of rotors to quantify the messages. No effective Cryptanalyse against it for its period of startup was revealed to date.

History

Well before the Second world war, it was clear for the American cryptographes that the mechanical movement with simple master key of the rotors of the new machines (Machine of Hebern) introduced recognizable diagrams into the quantified texts which could be used as a basis for the cryptanalytic attacks. William Friedman, director of the Signals Intelligence Service (LOCATED) of the US Army invented a system to correct this fault while making random the movement of the rotors. Its modification consisted of a reader of paper ribbon of a teleprinter attached to an apparatus with metal “tentacles” positioned to conduct electricity through the holes. For any letter pressed on the keyboard, not only the machine scrambled the letters with the mode of the other rotor apparatuses, but the holes in the ribbon at this place induced a projection of the rotors concerned, before the ribbon itself does not advance. Architecture resulting from these modifications was produced only in small quantity like the M-134 , and in addition to the usual parameters of initialization of the machine - that it had in common with Enigma among others - one added the positioning of the ribbon and the adjustments, via a control panel, association between each line of holes and the rotor which is dependant for him.

M-134 had the disadvantage, compared with Enigma, that the ribbon was to be identical for all the machines envisaged to the deciphering of its messages. If the ribbon had suddenly been intercepted, the number of adjustments important but not infinite would have called into question the reliability of its use. Moreover, the conditions of use on the battle fields made problematic the brittleness of certain ribbons.

The associate of Friedman, Frank Rowlett, then contributed his share to the method of advanced rotors by changing those. That can appear obvious but it was a question of creating rotors making it possible to generate one to five output signals for only one in entry - that thus made it possible to advance one or more rotors - there or Enigma made for a .

The budget allocated with the deciphering was weak with the the United States of America before the Second world war, therefore Friedman and Rowlett built a succession of extensions called SIGGOO (or M-229) which were used with M-134 in the place of the reader of ribbon. They were external boxes containing a parameter setting via three rotors which allowed five active entries, as if one pressed five keys at the same time on Enigma, and the exits were also gathered in groups of five - i.e. the letters of has to E would be cabled together for example. In this manner the five entry signals are randomized via the rotors, and arise on other side like only one signal on one of the five lines. The movement of the rotors could be controlled by a code renewed each day, and them paper bands were destroyed. This machine, assembly of several boxes, was called M-134-C.

In 1935 they showed their work with a cryptographe of US Navy with OP-20-G, Wenger. It found there little interest until 1937, when it made of it demonstration with the Commander Laurance Safford, the equivalent of Friedman at the office of naval espionage ( Office off Naval Intelligence ). Immediately noting the potential of the apparatus, him and the Commander Seiler added many accessories to make it easier to build. The result was the Electric Computer code Mark II (or ECM MArk II), which was produced as CSP-889 (or 888).

Curiously, the Army was unaware of these changes very as much as the mass production of the system. It was put in the secrecy in 1940. In 1941 the Army and US Navy met in a common cryptographic system based on this machine. The Army then started to use SIGABA.

Description

SIGABA was identical to the Enigma for the basic theory, in this that series of rotors were used for crypter each character of the clear text in a different character in the quantified text. However, contrary to the three rotors of Enigma, SIGABA did not include/understand any less than fifteen.

To be satisfied to increase the number of rotors does not make a surer machine. Because in the Enigma system, the rotors turn only if that which is on their line turns initially, which arrives after the striking of 26 characters. In other words the message must contain at least 676 (26 ²) characters before the third rotor does not turn, and approximately 17000 so that the fourth between concerned. For the majority of the messages of a few hundreds of characters, more rotors does not add safety.

With the additional rotors, SIGABA increased the complexity of movement of the principal rotors. In the Enigma the rotors turned of a notch to each struck character, which led to certain numbers of reasons repeating itself in the encrypted text. These reasons being difficult to find, the British and the Americans made important efforts on this problem, and at the end of the war they were able to practically read all the German quantified communications.

In the case of SIGABA, a simple modification was installation to make the machine sourer. Instead of turning thanks to a mechanical action pulled by the keyboard, the rotors turned by the electric action of a separate whole of rotors. SIGABA had three banks of five rotors each one; the action of two of the banks controlled rotations of the third.

• the rotors of the principal bank were called rotors of coding , and each one presented 26 contacts. Their role was the same one as in the other rotor machines, like Enigma; when a letter of the clear text had entered, a signal entered on a side of the bank and left the other, giving the encrypted letter.

• the rotors of the second bank were called rotors of control . They were also rotors with 26 contacts. The rotors of control received four signals with each step. At the conclusion of the rotors of control, the exits were divided into ten groups of variable sizes, from 1 to 6 wire. Each group corresponded to a wire of entry for the next bank of rotors.
• the rotors of the third bank were called rotors of index . These smaller rotors presented only 10 contacts, and did not turn during coding. After the crossing of the rotors of index, one to four of the five lines of exits led a current. These electrical signals involved then the movement of the rotors of coding.

In short, SIGABA used one or more its principal rotors in a complex way, Pseudo-aléatoire. The repetition of particular reasons, used to break the Enigma code, did not exist any more. In fact, even in possession of the clear text, there exists as well of possibilities of entries for encoding as it is difficult to calculate the number of it.

But SIGABA had also disadvantages: its important size and its weight, its high price, its difficulty of use, its mechanical complexity and its brittleness. That had nothing to do with a practical device like Enigma, which was smaller and light that the radios with which one used it. SIGABA was very much used in the radio rooms of the ships of US Navy, but could not be used on a battle field, and, in the majority of the theaters of operations, other systems were used, especially for the tactical communications. The most famous system is perhaps the use of Indians Navajo (wind talker) for the tactical communications on the battle fields in the Pacific, system set up the first time for Guadalcanal. In other tactical theaters, less sour but smaller, light and robust machines were used.

See too

• Typex

References

• Rowlett wrote a book on SIGABA (Aegean Close, Laguna Hills, California).
• Michael Lee, " Cryptanalysis off the Sigaba" , Masters Thesis, University off California, Santa Barbara, June 2003 (pdf).
• John J.G. Savard and Richard S. Pekelney, " The ECM Mark II: Design, History and Cryptology" , Cryptologia , Flight 23 (3), July 1999, pp211-228.

External bonds

• Electronic Cipher Machine (ECM) Mark II of Rich Pekelney
• Simulator SIGABA for Creative Windows
• of tables of code for Simulator SIGABA (Windows 2000-XP) Installation with the format .msi
• The ECM Mark II, aka SIGABA, M-134-C, and CSP-889 - of John Savard
• Code in language Java to simulate coding SIGABA

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