What is a Substitution Cipher?

A substitution cipher is a type of cipher in which the characters of a plaintext are substituted with other characters or patterns. For example, Rot13 is a special case of substitution cipher in which the letters were shifted instead of evenly mixed.

Special cases of Substitution Ciphers

Rot 13

Rot13 is a special case of substitution cipher in which the letters were shifted along the alphabet by 13 spaces instead of evenly mixed. In other words, each letter is replaced by the letter 13 spaces down. Thus, the Rot13 ciphers and similar rotation ciphers can be solved as substitution ciphers.

Atbash Cipher

Atbash cipher is a special case of substitution cipher in which the letters are replaced by its reverse instead of evenly mixed. In other words, the first letter becomes the last letter, the second letter becomes the second to last letter, and so on. Thus, the Atbash cipher can be treated as a substitution cipher. Messages can also be encrypted or decrypted using this CyberChef recipe.

Decrypting

Because substitution ciphers substitutes only the characters (and not the spaces), this allows us to look for common words and short words when decoding by hand. We can guess letters and try guessing the key. The more correct the key is, the more the resulting text would look like English (or the language it was encoded in). Similarly, there are also automated tools that do the guess and check process automatically.

• Automated solver with multiple languages at www.guballa.de
• Another automated solver at planetcalc.com
• Another automated cipher cracker at ciphertools.co.uk
• Manual solving tool at dcode.fr

Encrypting

Substitution ciphers are implemented by CyberChef too. This CyberChef recipe allows you to encrypt text using a substitution cipher. Just remember to change the ciphertext setting to your own secret key.