We could use Steganography. This is the act of actually hiding of a message to keep it secret. Whether it is encrypted or not does not matter so much if no-one knows it exists. This word comes from the Greek 'steganos' meaning 'covered' & 'graphein' meaning 'to write'.

Herodotus (484-425BC) seems to be about as far back as we have discovered early secret writings. He lived in the fifth century BC and he stated that the art of secret writing was what saved Greece from being conquered by Xerxes (520-465BC), the king of Persia.

Another example of Steganography is the microdot used in the second world war or invisible ink that can be made out of a mixture of 1oz of alum and a pint of vinegar and used to write on hard boiled eggs, or the 'milk' of the thithymallus plant. This dries invisible, but shows with gentle heating as does urine or many other carbon rich liquids.

Cryptography can be sub-divided into two branches. These are known as 'transposition' and 'substitution'. Transposition is effectively an anagram of the original word of message. This is quite a difficult thing to convert back if the process is done in a random way. For instance if a 35 letter message where to be scrambled in this way it would result in a 5x10ˆ31 possible different ciphers. This would take the entire population of earth, translating one possible cipher every second 1,000 times the lifetime of the universe to check every possible arrangement and in the process turn up many different possible and meaningful sentences. It would not only be impossible to unscramble, but also impossible to decide which one of the many unscramblings was the correct one.

Substitution is when each letter is changed for another in an organised way. The Caesar substitution cypher is one of the most well known. This shifts all the letters a certian amount of spaces, so if this was a move of 4, then A would become E and so on. With the discovery of language analysis, and general letter distribution, it became quite easy to decypher this type of encryption, however, it can be made more secure by using a Vigenère cypher. This is so named after the French person Blaise de Vigenère. He would use a grid with the letters moved over in each row by one more place than the previous row. He would then use a word or sentence to decide on which character the cypher text would use, thus each character would have a different row used to transpose the letter to its cypher equivalent.

The example below shows the word 'Hello' being encyphered using the key word 'Greeting' (this is not the best key to use as it has a double e in it. On a long message, it would be good to use a passage from a book or article). This results in the cyphertext of 'NVPPH'

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