The Caesar or Shift Cipher
In cryptography, a Caesar cipher, also known the shift cipher, or Caesar shift, is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet. For example, with a shift of 3, A would be replaced by D, B would become E, and so on. The method is named after Julius Caesar, who used it to communicate with his generals (wikipedia)
In the example on the left the 26 letters of the alphabet are shifted by 13 letters. The interactive demonstration below includes the 94 available ASCII characters. The first ASCII character " " (i.e. the space) has an ASCII value of 32. The final ASCII character "~" has an ASCII value of 125.
Execute an encryption by typing in a plain text message, an integer key, and clicking the "Encrypt" button. The arithmetic to execute the shift is performed in mod 94, so any integer from 1 to 93 will do. In mod 94, 94=0, 95=1, etc. You can decrypt the message by cutting and pasting the result into the plain text box and entering the negative of the original key. Now you may use this page to send secret messages to your friends and colleagues.