## Caesar Shift CipherThis, by modern standards, is a simple encryption method. It uses what is called a monoalphabet substitution cipher and was probably the first cipher to have been devised. It is called a Caesar shift cipher as the technique used to encrypt and decrypt messages was known to have been used by Julius Caesar. In the cipher used by Julius Caesar, he simply replaced one letter of plain text with a letter shifted by three places. Using our modern Latin alphabet, the letter 'I' would be replaced by the letter 'L'. So, as an example, the encryption of JULIUS CAESAR would be MXOLXV FDHVDU. Of course, we do not have to always shift the letters by three places. Using just the uppercase alphabet, we can shift it by 1 to 25 places. If we had used a shift of four places, the encryption of JULIUS CAESAR would be NYPMYW GEIWEV. In order to decrypt the message the recipient needs to know the number of places the letters have been shifted. This information is known as the key. In our encryption facility, we use an alphabet of both upper and lower case letters plus numbers. This gives 62 possible variations of encrypting the message - which gives 62 different keys. Our key consists of a single character of information. It is the letter or number that the plain text "A" is encrypted to. When encrypting using a Caesar shift of three places, the key is "D" as "D" is three places after the letter "A". |