Syko SD2 Strip Cipher
Circa: 1940

This cipher system was used by the British Army and Royal Air Force at the start of World War II.  SYKO was not secure and was only used for short messages. A daily start point was agreed upon in advance and paper strips of letters were moved up or down in an agreed pattern in order to encrypt the letters of the message one by one.

Please refer to the  RAAF Syko manual for additional information.

The plate below the strip cipher is the hinged lid. (Photo by Ralph Simpson)

Contributors and Credits:

1) Ralph Simpson <ralphenator(at)>
2) Science Museum  Exhibition Road, London SW7 2DD

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Dec 2/18