Lacida

Encyclopedia : L : LA : LAC : Lacida

Cipher Bureau [http://encycl.opentopia.com/ edit ]
Cryptologic methods and technology:
Lacida • Grill • Clock • Cyclometer • Card catalog • Bomba • Zygalski sheets
Location:
Saxon Palace • Kabaty Woods • PC Bruno • Cadix
Personnel:
Maksymilian Ciężki • Jan Graliński • Jan Kowalewski • Gwido Langer • Stanisław Leśniewski • Stefan Mazurkiewicz • Wiktor Michałowski • Antoni Palluth • Franciszek Pokorny • Marian Rejewski • Jerzy Różycki • Wacław Sierpiński • Piotr Smoleński • Henryk Zygalski

Diagram of Polish Lacida rotor cipher machine. A: Rotor-lid fasteners. B: Rotor-drive-spring pull. C: Cable from encryption box to electric typewriter. D: Cipher-decipher switch. E: Indicator drive. F: Letter windows. G: Encryption box. H: Rotor finger-wheels.

The Lacida (or LCD) was a rotor cipher machine designed before World War II by the Polish Cipher Bureau for wartime use by Polish higher commands. Its name derived from the initials of Gwido Langer, Maksymilian Ciężki and Leonard Stanisław Danilewicz and/or his brother, Ludomir Danilewicz.

Two LCDs had been sent to France prior to the invasion of Poland in September 1939. The LCD was used by the Polish Team Z at the Polish-, Spanish- and French-manned Cadix radio-intelligence and decryption center at Uzès, near France's Mediterranean coast, from spring 1941.

Prior to production, the machine had never been subjected to rigorous decryption attempts. Now it was decided to remedy this oversight. In early July 1941, Polish cryptologists Marian Rejewski and Henryk Zygalski received LCD-enciphered messages that had been transmitted a few days earlier to the staff of the Polish Commander-in-Chief, in London. Breaking the first message, given them July 3, took the two cryptologists all of a couple of hours. Further tests yielded similar results.

Rejewski explained in 1974 that the LCD had two serious flaws. It lacked the commutator ("plugboard") that was one of the German Enigma machine's strong points. The machine's other weakness involved the reflector and wiring. These shortcomings did not imply that the LCD, somewhat larger than Enigma and more complicated (e.g., it had a switch for resetting to decipherment) was easy to solve. The likelihood of its being broken by the German E-Dienst was judged to be slight; theoretically, however, it did exist. Col. Langer suspended use of the LCD at Cadix.

References

• K. Gaj, "Polish Cipher Machine - Lacida," Cryptologia, 16 (1), January 1992, pp. 73–80.
• Władysław Kozaczuk, Enigma: How the German Machine Cipher Was Broken, and How It Was Read by the Allies in World War Two, edited and translated by Christopher Kasparek, Frederick, MD, University Publications of America, 1984.

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