Caesar

History

One of the earliest ciphers is the Caesar cipher which, according to the Roman historian Gaius Suetonius Tranquillus (c. 70 AD-c. 135 AD) in his book Life of Julius Caesar written c. 121 AD, was used by the Roman general and statesman Julius Caesar (100 BC-44 BC) to exchange messages with Marcus Tullius Cicero (106 BC-43 BC) and others.

Description

The cipher is the simplest of all substitution cipher in which plaintext letters are replaced by letters three places further along in the alphabet so a=D, t=W, x=A. Any letter shift between 1 and 25 can be used. As there are only 25 possible keys it makes this cipher very insecure and easy to solve by testing every letter shift. The ROT13 cipher is a special case of the Caesar cipher with a letter shift of 13 where a=N, n=A, b=O, o=B and so on.

Example

Encipher the following Julius Caesar quote "Experience is the teacher of all things.” using the letter shift 3 gives:

Plaintext: ABCDEFGHIJKLMNOPQRSTUVWXYZ

Ciphertext: DEFGHIJKLMNOPQRSTUVWXYZABC

Experience is the teacher of all things

HASHULHQFH LV WKH WHDFKHU RI DOO WKLQJV

Solving

Caesar ciphers can be solved by selecting this option from the Tools tab. Type or paste from the clipboard the Caesar enciphered text into the top field then press return. The possible solutions will be displayed in the bottom window preserving any punctuation.

For longer Caesar ciphertexts the Aristocrat or Patristocrat cipher type can be used.