The keyword cipher is one you use a keyword to shuffle the letters of the alphabet. The keyword matches to the first few letters of the alphabet, and then any unused letters follow. For example, let's create a keyword cipher using the word "zebra" as the keyword. First, we write the alphabet out normally. Below this, we write the word "zebra", matching against the first five letters. Then, we write out all the other letters in order.
| 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 |
| Z | E | B | R | A | C | D | F | G | H | I | J | K | L | M | N | O | P | Q | S | T | U | V | W | X | Y |
We can choose any keyword. If the keyword has repeating letters, we just ignore them as we make the cipher. For example, if we make a cipher using "bookmark" as a keyword, we get:
| 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 |
| B | O | K | M | A | R | C | D | E | F | G | H | I | J | L | N | P | Q | S | T | U | V | W | X | Y | Z |
They are fairly easy to use because all you need to decipher them is the keyword used to create them. We could pass the information at the start of the message, like this:
[ZEBRA] CMPSTLA CZUMTPQ SFA CMMJGQF
