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Using this system, the keyword " zebras" gives us the following alphabets: Traditionally, mixed alphabets may be created by first writing out a keyword, removing repeated letters in it, then writing all the remaining letters in the alphabet in the usual order. The cipher alphabet may be shifted or reversed (creating the Caesar and Atbash ciphers, respectively) or scrambled in a more complex fashion, in which case it is called a mixed alphabet or deranged alphabet. Substitution of single letters separately- simple substitution-can be demonstrated by writing out the alphabet in some order to represent the substitution. In ROT13, the alphabet is rotated 13 steps. ROT13 is a Caesar cipher, a type of substitution cipher. 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. 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. There are a number of different types of substitution cipher. 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. 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. Substitution ciphers can be compared with transposition ciphers. The receiver deciphers the text by performing the inverse substitution process to extract the original message. 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. JSTOR ( March 2009) ( Learn how and when to remove this template message).Unsourced material may be challenged and removed.įind sources: "Substitution cipher" – news Please help improve this article by adding citations to reliable sources. This article needs additional citations for verification.