The Modern C++ Challenge

88. Caesar cipher

A Caesar cipher, also known as Caesar’s cipher, Caesar’s code, Caesar shift, or shift cipher, is a very old, simple, and widely known encryption technique that substitutes each letter in the plain-text with a letter some fixed number of positions down the alphabet. This method was used by Julius Caesar to protect messages of military importance. He used a shift of three letters, therefore replacing A with D, B with E, and so on. In this encoding, the text CPPCHALLENGER becomes FSSFKDOOHQJHU. The cipher is described in detail on Wikipedia at https://en.wikipedia.org/wiki/Caesar_cipher.

Although the Caesar cipher has no place in modern cryptography since it is trivial to break, it is still used on online forums or newsgroups ...