New York, 1942: checking mail for anything that might aid the enemy (Image: Bettmann/Corbis)
A history of secret messages that runs from lemon juice to codes in digital photos, Prisoners, Lovers, and Spies doesn鈥檛 quite live up to its glamorous title
THE notion that 鈥済entlemen do not read each other鈥檚 mail鈥� troubled the FBI when it set up a postal censorship operation in the second world war.
Advertisement
But as science historian Kristie Macrakis explains in Prisoners, Lovers, and Spies 鈥� a history of 鈥渟ecret writing鈥� 鈥� the British had no such scruples following their success catching spies in the first world war. And intercepting other people鈥檚 communications didn鈥檛 trouble the CIA or KGB in the cold war either, nor the US National Security Agency in recent times.
So what is secret writing? Cryptographers wrestle with messages contained in a sequence of letters, numbers or symbols; detecting secret writing, however, means finding the message in the first place. The most famous method is invisible ink, which is revealed by heat or a chemical reagent. An old favourite, lemon juice, was used by Nazi spies in the UK, who could be convicted on little more than the possession of lemons and used matches.
But the loss of its spies sparked an arms race: Germany refined microdot technology 鈥� shrinking photographed documents to the size of a full stop 鈥� and new chemicals that required specific reagents, while the Allies hunted for a universal developer to reveal all messages. The race continues, as terrorists hide messages in digital photos, and superagencies hoover up all the electronic communications they can.
Not unlike the subject matter, the book proceeds in fits and starts, with most cutting-edge development and excitement centred on war or other emergencies. Yet it never quite lives up to the glamour of the title.
Still, if you fancy trying out secret writing, Macrakis has some tried and tested recipes, which use easily obtained substances. But remember: for every message you send, there has to be someone 鈥� not a gentleman 鈥� who is happy to read your mail.
Yale University Press
This article appeared in print under the headline 鈥淩evealing all鈥�
