The Chaocipher is a cipher method invented by J. F. Byrne in 1918 and described in his 1953 autobiographical Silent Years. He believed Chaocipher was simple, yet unbreakable. Byrne stated that the machine he used to encipher his messages could be fitted into a cigar box. He offered cash rewards for anyone who could solve it.
In May 2010 the Byrne family donated all Chaocipher-related papers and artifacts to the National Cryptologic Museum  in Ft. Meade, Maryland, USA. This led to the disclosure of the Chaocipher algorithm.