Substitution Cipher

Dividing Line


A Substitution Cipher is a method of encryption that has been in use for hundreds of years. 

To encrypt a message so no one else can read it, you change every letter in your message for a different letter.


Here is an example of how to encrypt a message using a Substitution Cipher. The text we are encrypting is "defend the east wall of the castle".

Keys for the simple substitution cipher are the 26 letters of the alphabet.  An example key is ...

plain alphabet : abcdefghijklmnopqrstuvwxyz
cipher alphabet: phqgiumeaylnofdxjkrcvstzwb

An example encryption using the above key ...

plain text : defend the east wall of the castle
cipher text: giuifg cei iprc tpnn du cei qprcni

You can see that a letter from your original message is replaced by another letter.

Decrypting the message is just as easy! You just need to replace the cipher character with the plain text character.

TaskHave a Go

Plain Text

key =

Remove Punctuation

Cipher Text


Last modified: Friday, 22 February 2019, 10:04 PM