When back doors backfire

WITHOUT encryption, internet traffic might as well be written on postcards. So governments, bankers and retailers encipher their messages, as do terrorists and criminals.For spy agencies, cracking methods of encryption is therefore a priority. Using computational brute force is costly and slow, because making codes is far easier than breaking them. One alternative is to force companies to help the authorities crack their customers’ encryption, the thrust of a new law just passed in China and a power that Western spy agencies also covet. Another option is to open “back doors”: flaws in software or hardware which make it possible to guess or steal the encryption keys. Such back doors can be the result of programming mistakes, built by design (with the co-operation of the encryption provider) or created through unauthorised tinkering with software—or some combination of the three.