Codes and Ciphers

Codes and ciphers are forms of secret communication. A code replaces words, phrases, or sentences with groups of letters or numbers, while a cipher rearranges letters or uses substitutes to disguise the message. The technology of such secret communication is called cryptology.

Secret writing has been employed about as long as writing has existed. Cryptology has long been employed by governments, military, businesses, and organizations to protect their messages. Today, encryption is used to protect storage of data and transactions between computers.

Ciphers are broken into two main categories; substitution ciphers and transposition ciphers. Substitution ciphers replace letters in the plaintext with other letters or symbols, keeping the order in which the symbols fall the same. Transposition ciphers keep all of the original letters intact, but mix up their order. The resulting text of either enciphering method is called the ciphertext. Of course, you can use both methods, one after the other, to further confuse an unintended receiver as well.

Here are some more popular ciphers. They are links so you can click on them to learn more.


Letter Number Cipher
Caesar Substitution Cipher
Key Word Substitution Cipher
Keyword Number Ciphers
Transposition ciphers
The Bacon Cipher
Pigpen Cipher
QWERTY cipher
Telephone Keypad Cipher
Polybius Square Cipher
Atbash Cipher