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The Polybius square has also been used in the form of the "knock code" to signal messages between cells in prisons by tapping the numbers on pipes or walls. [2] It is said to have been used by nihilist prisoners of the Russian Czars and also by US prisoners of war during the Vietnam War .
The pigpen cipher uses graphical symbols assigned according to a key similar to the above diagram. [1]The pigpen cipher (alternatively referred to as the masonic cipher, Freemason's cipher, Rosicrucian cipher, Napoleon cipher, and tic-tac-toe cipher) [2] [3] is a geometric simple substitution cipher, which exchanges letters for symbols which are fragments of a grid.
The first Code-O-Graph, called the "Mystery Dial" unit, was introduced in 1941, as a device to enable Secret Squadron agents in the field to send and receive secure messages. It was in badge form, as were the next three models. The front of the badge displayed the number and cipher alphabet scales.
The Enigma machine was considered so secure that it was used to encipher the most top-secret messages. [1] The Enigma has an electromechanical rotor mechanism that scrambles the 26 letters of the alphabet. In typical use, one person enters text on the Enigma's keyboard and another person writes down which of the 26 lights above the keyboard ...
"The Alphabet Cipher" was a brief study published by Lewis Carroll in 1868, describing how to use the alphabet to send encrypted codes. [1] It was one of four ciphers he invented between 1858 and 1868, and one of two polyalphabetic ciphers he devised during that period and used to write letters to his friends.
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The resulting message, 3113212731223655 has to be secured by other means if the straddling checkerboard table is not scrambled. By passing digits through an additional transposition or substitution cipher stage can be used to secure message -- to whatever extent transposition or substitution can be considered secure.
The Cardan grille was invented as a method of secret writing. The word cryptography became the more familiar term for secret communications from the middle of the 17th century. Earlier, the word steganography was common. [citation needed] The other general term for secret writing was cypher - also spelt cipher. There is a modern distinction ...