We finished the previous chapter (see Section 21.2) by stating that the file trarfvf.txt contains a text coded with a substitution cipher with the shift (rotation) of 13 characters. This turns out to be the Caesar cipher used by the famous Roman emperor in antiquity (breaking the cipher without a computer program and sufficient amount of text is not an easy task).
So here is an exercise for you, write a computer program that can code and decode a textual message with a substitution cipher of any shift. Use it to decrypt the message contained in trarfvf.txt (~31 KiB). Feel free to decipher the file name (trarfvf) itself as well.