Caesar cipher is an encryption method named after Julius Caesar, in which messages were encrypted with a substitution c ipher. In principle, Caesar used a simple rotation method with monoalphabetic substitution, in which the letters were offset by three digits.
In the Caesar cipher, the letters of the plaintext are substituted with an alphabetic letter offset of three letters. For the letter "A" the letter "D" is taken, for "B" the "E", for "C" the "F" and so on. Thus, the plaintext word KIRCHE in the ciphertext becomes the letter combination NMUFKH. The recipient of the ciphered message needs the key for decryption, which in Caesar encryption is called: "Each letter is replaced by the third preceding letter".
Since this letter offset can also be interpreted as a rotation, the Caesar cipher is also called ROT3, a rotation by three letters. Such a 13-letter rotation, called ROT13, is available in some Web browsers to protect messages against unintended reading. The substitution code of rotation methods can be decrypted too quickly by trying all 25 offset possibilities.