# Substitution Cipher

In cryptography, a substitution cipher is a method of encryption by which units of plaintext are replaced with ciphertext, according to a regular system; the "units" may be single letters (the most common), pairs of letters, triplets of letters, mixtures of the above, and so forth. The receiver deciphers the text by performing an inverse substitution.

Substitution ciphers can be compared with transposition ciphers. In a transposition cipher, the units of the plaintext are rearranged in a different and usually quite complex order, but the units themselves are left unchanged. By contrast, in a substitution cipher, the units of the plaintext are retained in the same sequence in the ciphertext, but the units themselves are altered.

There are a number of different types of substitution cipher. If the cipher operates on single letters, it is termed a simple substitution cipher; a cipher that operates on larger groups of letters is termed polygraphic. A monoalphabetic cipher uses fixed substitution over the entire message, whereas a polyalphabetic cipher uses a number of substitutions at different positions in the message, where a unit from the plaintext is mapped to one of several possibilities in the ciphertext and vice versa.

### Other articles related to "substitution cipher, cipher, ciphers":

Types of Classical Ciphers - Substitution Ciphers
... In a substitution cipher, letters (or groups of letters) are systematically replaced throughout the message for other letters (or groups of letters) ... 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 alphabet ...
Atbash
... Atbash is a simple substitution cipher for the Hebrew alphabet ... The Atbash cipher for the modern Hebrew alphabet would be Plain אבגדהוזחטיכלמנסעפצקרשת Cipher תשרקצפעסנמלכיטחזוהדגבא An Atbash cipher for the ... This is a very simple substitution cipher ...
Japanese Cryptology From The 1500s To Meiji - The Two-Letter, Ten-Chart Code
... This is just a code version of a polyalphabetic substitution cipher ... Polyalphabetic ciphers use several different enciphering alphabets and change between them at some interval, usually after every letter ... The strength of a polyalphabetic cipher comes from how many alphabets it uses to encipher, how often it switches between them, and how it switches between them ...
Substitution Ciphers in Popular Culture
... Sherlock Holmes breaks a substitution cipher in "The Adventure of the Dancing Men" ... The Al Bhed language in Final Fantasy X is actually a substitution cipher, although it is pronounced phonetically (i.e ... The Minbari's alphabet from the Babylon 5 series is a substitution cipher from English ...
Ciphertext - Types of Ciphers - Historical Ciphers
... Historical pen and paper ciphers used in the past are sometimes known as classical ciphers ... They include Substitution cipher the units of plaintext are replaced with ciphertext (Caesar cipher and One-time pad) Transposition cipher the ciphertext is a permutation of the plaintext (Rail ... Many of the classical ciphers can be cracked using brute force or by analyzing only ciphertext with the exception of the one-time pad ...

### Famous quotes containing the words cipher and/or substitution:

The eye is the first circle; the horizon which it forms is the second; and throughout nature this primary figure is repeated without end. It is the highest emblem in the cipher of the world.
Ralph Waldo Emerson (1803–1882)

To play is nothing but the imitative substitution of a pleasurable, superfluous and voluntary action for a serious, necessary, imperative and difficult one. At the cradle of play as well as of artistic activity there stood leisure, tedium entailed by increased spiritual mobility, a horror vacui, the need of letting forms no longer imprisoned move freely, of filling empty time with sequences of notes, empty space with sequences of form.
Max J. Friedländer (1867–1958)