The first DECODELE secret message is written in a Random Letter Substitution cipher.

In a random letter cipher, the letters of the alphabet are mixed up in a random (no special) order, and then each of those letters is assigned a letter in the real alphabet.

The coded message is written by substituting a random letter for each of the real letters in the message you want to send. (the coded message is sometimes called the “cipher text” and your uncoded message is called the “plain text.”)