The history of encryption

480 BC

It’s said that, during the Greek and Persian war of 480BC, an emissary was sent with a hidden message urging Aristagoras of Miletus to revolt against the Persian king. The message was tattooed on his shaved scalp and his hair was then allowed to grow back to full length. This is perhaps the first recorded example of steganography, or covered writing.

But what of cryptography – literally, hidden writing? The conversion of text (or computer code) into a cipher or code – encryption, in other words – is nothing new. However, you may be surprised at just how far back in history the obfuscation of information using a secret key actually stretches.

 

3rd century BC

The oldest known encryption device is the scytale, or Spartan Stick. The sender would wrap a parchment belt around a stick, or scytale, and then write the message along its length. Unwrapped, the result was gibberish.
Only when a stick of exactly the same diameter was used to re-wrap the belt would the message become legible once more.

 

44BC

You need to jump forward to 44BC and the Roman Emperor Julius Caesar to get a true cipher in real-world use. Caesar used a substitution cipher technique, shifting letters by a known set amount (for instance, A becomes E, B becomes F, C becomes G, and so on), to good effect during the Gallic wars, sending secret messages to his generals.

 

9th century

Wherever there are code makers there will be code breakers, and this has been true throughout history. Take the 9th-century code breakers of Baghdad, who worked out that in a monoalphabetic cipher that replaces a letter with a symbol, there is a flaw, in that frequency stays constant. For example, if the number five appears in a message more often than any other character, it is probably hiding an E – the most commonly used letter in the English language.

 

1467

Leon Battista Alberti probably had the biggest impact upon cryptography for centuries when, in 1467, he invented the polyalphabetic cipherdisk. The use of separate alphabets on concentric rings was a revelation, not least because they hide those frequency patterns, so an E might still be represented as five if it appears as an even letter, but could be a seven if it is an odd one. The World War Two Enigma machine is perhaps the most famous example of a polyalphabetic cipher.

 

18th century

Thomas Jefferson further developed the cipher wheel concept when he built one consisting of no fewer than 36 wooden wheels on a central  rod, each engraved with a scrambled alphabet.
This could create a 36-letter message on one row and be encoded simply by writing the letters from another row. Recreate that jumbled text and the message reveals itself. In fact, this simple idea was so efficient that the US Navy successfully used a variation on the strip cipher in World War Two.