Caesar Cipher Encryption and Decryption using Python. ROT13 cipher is a special case of the Ceaser cipher in which the shift(key) is always 13. The ROT47 (Caesar cipher by 47 chars) is a simple character substitution cipher that replaces a character within the ASCII range [33, 126] with the character 47 character after it (rotation) in the ASCII table. It is an invertible algorithm i.e. applying the same algorithm to the input twice will get the origin text. This is really useful in CTF (Capture the Flag) tournaments where the flags or clues are commonly encrypted using Caesar Cipher.