Key Word Substitution Cipher

A key word cipher is created by taking a key word or phrase and put the letters in order at the start of the Ciphertext (eliminating any redundant letters) and then complete the cipher by writing down the remaining letters of the alphabet in alphabetical order (leaving out the letters you’be already used in your key word or phrase).
For example: Let’s make our key word KEY


Now let’s use a key where there are redundant letters (letters that are repeated)

For example: Let’s make our key word CROCODILE
If there are any redundant letters (letters that are repeated) write the word without them. CROCODILE has two repeated letters, C and O, so writing CROCODILE without the repeated letters we get CRODILE. This begins our cipher after which we put the rest of the letters of the alphabet in alphabetical order (leaving out the letters you’ve already used in your key word or phrase).




A key word substitution cipher is much like a Caesar shift cipher, but instead of knowing the number of the shift, one needs to know the key word or phrase in order to decipher it.