Ciphers: Substitution

Substition ciphers are the simplest form of encrypting a text. They involve switching a letter in the original message with a different one to create the encrypted message. They can be achieved via shifting a letter, or by arbitrarily swapping a letter with another one, using a key to decide how it is swapped. The latter is always a superior method, but most substittion ciphers use simple shifting.

An example is:

Message: H E L L O

Encryption: S V O O L

In this case, the letters are replaced by reversing the common alphabet.