DURING the second world war, British code breakers were inadvertently handed the means to reading encrypted enemy radio messages. Sloppy U-boat captains relied on the same mathematical key to encrypt the messages for weeks at a time, or repeated formulaic phrases in a predictable way.
The story reminds us that there is no such thing as a perfect cipher. But that hasn’t stopped a lot of people claiming that quantum cryptography schemes will provide one. Impressed by their ingenuity, researchers have spread the word that the resulting technologies will offer what no classical scheme can: 100 per cent secure communication.…
