Caesar Cipher

  • The Caesar Cipher was an Encryption Code, a simple substitution cipher used by Julius Caesar (100-44 BCE) to encode messages.
  • It worked by substituting each letter with another, which was three letters up the alphabet.

Method

  • So:
    • ‘Beware the Ides of March’
  • Becomes
    • ‘Ehzduh wkh Lghv ri Pdufk’
  • Suetonius, specifically reveals this code by explaining that D substituted A, in his ‘The Life of Julius Caesar’

Use

  • The cipher avoided regular couriers reading confidential military or political plans.
  • In the event of interception by a determined Enemy, decryption was just simple task of guessing the number of letters displaced, but it still required time to decrypt.

Lost Ciphers

  • The grammarian Aulus Gellius in his ‘Attic Nights’  17.9.1-5. mentions a lost work by Probus (232-282 CE) on Julius Caesar’s letters which contained more complicated Ciphers.

Caesar's Box

  • This is another cipher, also named after Julius Caesar, but unlikely to have been used by him.
  • Take the coded message:
    • A long string of horizontal letters.
    • Divide it by its square root: 25 letters is 5, (16 letters is 4, etc.,)
    • Divide the message into groups of five.
    • Rearrange them into a box, one above the other:
    • The message can now be read down the vertical lines.
  • Example:
    • ESVNITAOOCNBLIIAICNLIGASY
      • E S V N I
      • T A O O C
      • N B L I I
      • A I C N L
      • I G A S Y
    • ‘Etna is a big Volcano in Sicily’

Other Ciphers

 

Posted in .