Cryptography/Substitution cipher

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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]

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

See also[edit]

External links[edit]

  • McClung, O. William: Substitution Cipher Cracker — a useful tool that will perform a frequency analysis on ciphertext.
  • CryptoClub: Crack a Substitution Cipher.
  • American Cryptogram Association: Solve a Cipher.
  • Olson, Edwin: Decrypto — a fast and automated cryptogram solver that can solve simple substitution ciphers often found in newspapers, including puzzles like cryptoquips and patristocrats.
  • Ciphergram Solution Assistant — solves, or nearly solves, ciphergrams like those in the newspapers that are called cryptoquotes.