Royal Signals Museum - Interactive Codes

Codes & Codebreaking

This site will be regularly updated.

Here you will learn the basics about how the Army, spies and agents have used codes to guard their secrets from the enemy. You will learn how to code and decode messages using some of the early codes that were used.

Since humans began writing, they have been communicating in code. This obsession with secrecy has had dramatic effects on the outcome of wars, monarchies and individual lives.

The oldest means of sending secret messages is to simply conceal them by one trick or another. The ancient Greek historian Herodotus wrote that when the Persian Emperor Xerxes moved to attack Greece in 480 BC, the Greeks were warned by an Greek named Demaratus who was living in exile in Persia. In those days, wooden tablets covered with wax were used for writing. Demaratus wrote a message on the wooden tablet itself and then covered it with wax, allowing the vital information to be smuggled out of the country.

The idea of obscuring the message so that it could not be read even if it were intercepted, and the result was "cryptography", Greek for "hidden writing". The result was the development of "codes", or secret languages, and "ciphers", or scrambled messages.
The distinction between codes and ciphers is commonly misunderstood. A "code" is essentially a secret language invented to conceal the meaning of a message. A "cipher" conceals a plaintext message by replacing or scrambling its letters. This process is known as "enciphering" and results in a "ciphertext" message. Converting a ciphertext message back to a plaintext message is known as "deciphering".

To see a selction of codes and code breaking activities please check link to a PDF file. This is a booklet designed by the Royal Signals Museum which explains and illustrates a variety of simple codes.

Codes & Code Breaking