Making and breaking codes is an "intellectual arms race" that has been under way for thousands of years. While modern computers have brought about nearly unbreakable codes, there is still the potential for new technologies and human ingenuity as a way around them.
The history and modern practice of encryption was the subject under discussion during last night's Irish Times/RDS Science Today lecture, given at the RDS Dublin, by the best-selling author, Dr Simon Singh. He based his talk on his new book, The Code Book: the science of secrecy from ancient Egypt to quantum cryptography.
The secret world he described was "an intriguing mixture of politics, history and science", Dr Singh told his audience.
The use of codes and their breaking had played an important part in history, deciding the outcomes of battles, causing lives to be saved or lost, and determining the fate of nations.
"Codes today are more important than every before," he said. "We live in an information world and information is a commodity." The lock and keys which controlled this commodity were codes.
Dr Singh searched back in time for examples of both code-making and steganography, the business of concealing messages which predates encryption.
Herodotus described an example in which a messenger's head was shaved, the message tattooed to his head and the hair allowed to grow back to conceal it. More modern examples of steganography included invisible ink and micro-dots.
"The problem is if someone finds the message, then everything is there to see," Dr Singh said, hence the introduction of cryptography. This did not seek to hide the message but to make it unreadable to anyone who found it bar the intended recipient, who would have the decoding key.
Julius Caesar discussed the use of cryptography and the Kama Sutra recommended that women should know how to use it, he said. "The essential idea is that you just substitute one letter for another."
The Arabs in their intensive studies of the Koran helped to break down early cryptography methods, however. They noted that no language made equal use of all its letters. Arabic makes most use of A and L, while the most favoured letter in English is E.
This knowledge helped the early code-breakers to make assumptions about the appearance of letters in a coded text. Even this limited knowledge allowed simple encryption codes to be broken.
Mary Queen of Scots lost her head over a broken code. While imprisoned by Elizabeth I, Mary sent coded messages to supporters outside, hidden in the bung of a beer barrel. She sanctioned an assassination plot against Elizabeth, but her codes were broken and she was put to death for treason.
Dr Singh discussed modern computer-driven code systems which used "public key cryptography", which eliminated the need to distribute secret code keys. Once encrypted, only the intended recipient had the numerical method to unlock the data.
"The code-makers today have a bigger lead than they have ever had before," he said. Modern codes were effectively unbreakable but there was always the potential for the use of advanced technology to intercept data before they could be encrypted. Thus the intellectual arms race between the coders and the code breakers would continue.
Mr Singh has prepared a 10-step coded message and challenges readers of his new book to beat the code and win a £10,000 prize. Details are available at the back of his book, The Code Breakers (Fourth Estate, £16.99 in the UK). Details are also available at the web site: http://www.4thestate.co.uk/ cipherchallenge
