This was a Finnish Cipher Device used by Finnish forces in the Continuation War against the Soviet Union.  It was manufactured from 1942 and was colloquially known as Matolaatikko, which translates to “wormbox” - a reference to its similarity to the wooden box used by anglers to store bait.  Plaintext is located on the horizontal ruler and is enciphered by letters appearing in the square tableau.  The ruler is moved down every five letters.  On reaching the lowest row the ruler is moved back up but also translated horizontally according to a session key.  The tableau is changed regularly.  Despite its simplicity, messages produced by the device were secure.

The Continuation War, also known as the Second Soviet-Finnish War, was a conflict fought by Finland and Nazi Germany against the Soviet Union from 1941 to 1944, as part of World War II.

M-42 front view. Click on image to enlarge.

M-42 carrying case

M-42 tableau example which consists of a matrix of 26 x 26 letters distributed randomly. It is held in place by two horizontal metal strips at the top and bottom of the page.  The narrow piece of paper is permanently stuck to the ruler and bears the alphabet arranged in order. Click on image to enlarge.

All photos in this table by Michael Smith

Contributor:

1) Michael Smith <msthylacine(at)gmail.com>

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April 13/23