Lacida

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The Lacida (also: LCD ) was a rotor key machine , which was developed between 1932 and 1935 by cryptographers at the Polish Biuro Szyfrów (BS) (German: "Chiffrenbüro"), manufactured by the Warsaw company AVA and for use in the Polish army was designed. The name Lacida was formed as an acronym from the first letters of the last names of its inventors Gwido Langer ("La"), Maksymilian Ciężki ("Ci") and Leonard Stanisław Danilewicz or his brother Ludomir Danilewicz ("Da"). Not a single surviving specimen is known of the Lacida.

construction

In reverse to the Enigma roller shown here, the Lacida rollers had spring-loaded contacts on their left side ...
... and fixed contacts on the right-hand side, but otherwise - with the exception of the number of contacts - were structured similarly.

The construction of the Lacida was based on the then commercially available portable typewriter from the US company Remington , which was used as an input and output unit. The typewriter was mounted on a large aluminum box in which there were a number of relays that could be used to operate the typewriter's type levers electromechanically . The most important element from a cryptographic point of view was placed immediately in front of it. This was the Kaseta szyfrujaca (German: "Encryption cassette"), that is, the unit that was responsible for the actual function of the machine, namely encryption and decryption . Within the key box, a total of eight encryption cylinders were arranged next to each other, similar to what is known from other rotor encryption machines . The contact points were arranged in a circle around the central axis on both sides of the rollers, and one contact on the left and one on the right were connected irregularly and in pairs by an insulated wire inside a roller.

The two outer rollers, the entry and exit rollers, i.e. the first and eighth rollers, were firmly mounted and could not rotate. The other (inner) rollers, on the other hand, were rotatable, whereby (viewed from the left) the second, fourth and sixth rollers were automatically advanced during operation of the machine and they continued to rotate each time a button was pressed. The third, fifth and seventh reels could only be set by hand and did not rotate. During encryption, the current flowed from the left, the “plain text page” so to speak , to the right, to the “ciphertext page” , through the set of rollers; reverse direction from right to left.

A special feature of the Lacida was the number of contacts on its rollers. The key rollers of other rotor machines usually have exactly 26 contacts, corresponding to the 26 capital letters of the Latin alphabet . The number of contacts of the Lacida, however, was unusual and amounted to 24, 31 or 35 contacts. The first two rollers had 24 contacts, the third roller also had 24 contacts, but only on its left side. On the right side she had 31 contacts. The fourth roller had 31 contacts on both sides, while the fifth had 31 contacts on the left but 35 contacts on the right. The remaining rollers had 35 contacts on both sides.

Correspondingly, the entire alphabet could not be used for encryption, but only the well-known 26 letters with the exception of two letters rarely used in Polish , one suspects Q and V. This restriction was ensured constructively by placing a mechanical panel over the Typewriter keyboard was pushed, which covered all number keys as well as the two letters mentioned.

In the decryption mode, however, this screen was pushed back. Now all 26 letters and the nine digits from 1 to 9 could be entered. The Lacida did not have a special key for the number zero . Instead, the almost identical-looking letter "O" was used. A total of 35 characters were available for the ciphertext (26 letters and 9 digits) and only 24 characters for the plain text.

As with other rotor machines, the rotating rollers on the Lacida were incremented similar to a mechanical odometer . That means, with every single button press the right rotating roller (roller no. 6) rotated one step further. When it had completed one revolution, i.e. after 35 steps, the middle rotating roller (roller no. 4) made one step. When it had also completed one revolution, i.e. here after 31 steps, then finally the left rotating roller (roller no. 2) made one step. That is, the period length of the Lacida was 24 * 31 * 35 = 26,040 characters.

The machine weighed about 40 kg and was powered by two batteries of 4.5 volts each.

history

The Lacida was developed roughly between 1932 and 1935. The exact date is not known. There are slightly contradicting statements. Presumably at least 40 copies were built by the Warsaw company AVA , possibly 125 pieces. Most of the machines, like almost the entire inventory of the Biuro Szyfrów , were destroyed by the Polish cryptologists shortly after the German attack on their land in September 1939 in order to remove them from German access. Only a few copies made it to London and Paris. The Poles who found asylum in France via Romania use the Lacida from there for secret communication with the Polish government- in- exile in London. In the summer of 1941, the two BS specialists , Marian Rejewski and Henryk Zygalski , were given the task of checking the safety of their own machine. They were given some radio messages encrypted with the Lacida. To the shock of those responsible, it took the two experienced code breakers less than two hours to break the slogans . As a result, further use of the Lacida was immediately prohibited and cryptographic improvements were sought. It is not known whether and how this happened. The details and the further history of the Lacida are lost in the chaos of war in the following years.

literature

  • Krzysztof Gaj: Polish Cipher Machine - Lacida . Cryptologia . Rose-Hulman Institute of Technology. Taylor & Francis, Philadelphia PA 16.1992,1, ISSN  0161-1194 , pp. 73-80.
  • Władysław Kozaczuk : Enigma: How the German Machine Cipher Was Broken, and How It Was Read by the Allies in World War II , edited and translated (in English) by Christopher Kasparek, Frederick, MD, University Publications of America, 1984, ISBN 0 -89093-547-5 , pp. 59-60.

Web links

Individual evidence

  1. ^ Krzysztof Gaj: Polish Cipher Machine - Lacida . Cryptologia . Rose-Hulman Institute of Technology. Taylor & Francis, Philadelphia PA 16.1992,1, ISSN  0161-1194 , p. 77.