The Chaocipher is a method of encryption invented by John F. Byrne in 1918 that was never publicly solved until the family allowed its secrets to be revealed in 2010. You can read about it here. The encryption uses two rotating disks on which is written a custom alphabet. The two disks are identical and linked with a kind of gearing (ratio 1:1) that if a disk is turned clockwise, the other turns counter-clockwise.