Cryptography/Substitution cipher

From Wikibooks, open books for an open world
Jump to navigation Jump to search

A Substitution Cipher is similar to a Caesar cipher, but instead of using a constant shift left or right, the plain alphabets and the cipher alphabets are mixed arbitrarily.

For example:

Plain Alphabet:  A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Cipher Alphabet: Z Y X W V U T S R Q P O N M L K J I H G F E D C B A

With the above, the Plain text "This is a sample" would encrypt to "Gsrh rh z hznkov." This particular substitution cipher, which relies on transposing all the letters in the alphabet such that the resulting alphabet is backwards, is known as an atbash cipher.

With Substitution Ciphers, the secret is in the mapping between the plain and cipher alphabets. However, there are several analytical techniques to help break these ciphers with only the ciphertext. See Frequency analysis

Solving substitution ciphers[edit | edit source]

English-language ciphers be solved using principles such as these:

See also[edit | edit source]

External links[edit | edit source]

  1. "Cryptoquip". Cryptoquip. Retrieved 2024-04-13.