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In cryptography, a substitution cipher is a method of encrypting in which units of plaintext are replaced with the ciphertext, in a defined manner, with the help of a key; the "units" may be single letters (the most common), pairs of letters, triplets of letters, mixtures of the above, and so forth.
The list of ciphers in this work included both substitution and transposition, and for the first time, a cipher with multiple substitutions for each plaintext letter. Charles Babbage , UK, 19th century mathematician who, about the time of the Crimean War , secretly developed an effective attack against polyalphabetic substitution ciphers.
By World War II, mechanical and electromechanical cipher machines were in wide use, although—where such machines were impractical—code books and manual systems continued in use. Great advances were made in both cipher design and cryptanalysis, all in secrecy. Information about this period has begun to be declassified as the official British ...
600-500 – Hebrew scholars make use of simple monoalphabetic substitution ciphers (such as the Atbash cipher) c. 400 – Spartan use of scytale (alleged) c. 400 – Herodotus reports use of steganography in reports to Greece from Persia (tattoo on shaved head) 100-1 A.D.- Notable Roman ciphers such as the Caesar cipher.
In a substitution cipher, letters, or groups of letters, are systematically replaced throughout the message for other letters, groups of letters, or symbols. A well-known example of a substitution cipher is the Caesar cipher. To encrypt a message with the Caesar cipher, each letter of message is replaced by the letter three positions later in ...
The main classical cipher types are transposition ciphers, which rearrange the order of letters in a message (e.g., 'hello world' becomes 'ehlol owrdl' in a trivially simple rearrangement scheme), and substitution ciphers, which systematically replace letters or groups of letters with other letters or groups of letters (e.g., 'fly at once ...
The Aristocrat Cipher is a type of monoalphabetic substitution cipher in which plaintext is replaced with ciphertext and encoded into assorted letters, numbers, and symbols based on a keyword. The formatting of these ciphers generally includes a title, letter frequency, keyword indicators, and the encoder's nom de plume . [ 1 ]
The ACA was formed on September 1, 1930. Initially the primary interest was in monoalphabetic substitution ciphers (also known as "single alphabet" or "Aristocrat" puzzles). This has since been extended to dozens of different systems, such as Playfair, autokey, transposition, and Vigenère ciphers.