== See also ==* Grille (cryptography)==References==* David Kahn, "The Codebreakers — The Comprehensive History of Secret Communication from Ancient Times to the Internet", 1996, ISBN 0-684-83130-9.
* David Kahn, The Codebreakers — The Comprehensive History of Secret Communication from Ancient Times to the Internet, 1996, ISBN 0-684-83130-9.