WHEN Barack Obama became American president, one of his first tussles with White House lawyers was over whether he could keep his beloved BlackBerry. (Yes, he did.) The reason why the lawyers were wary was that e-mail cannot be destroyed. People do not know where the information they are sending is being stored and when, if ever, it is deleted. Such unknowns make it possible for seemingly long-gone data to turn up in a court under the order of a subpoena, or worse, in the hands of a hacker. On August 13th, though, a team of computer scientists led by Roxana Geambasu of the University of Washington, Seattle will unveil to the 18th USENIX Security Symposium in Montreal an e-communications system that destroys messages soon after they have been sent. The technique devised by Ms Geambasu and her colleagues uses one of the least secure areas of the web to store encryption keys that self-destruct after a certain period. Peer-to-peer networks, or P2Ps, originated in the late 1990s with the rise of music-sharing networks such as Napster and KaZaA. Individual users would log on and allow other people to download music from their computers while simultaneously downloading music for themselves. In recent years P2Ps have become vast file-sharing networks for information in all its forms. Dr Geambasu and her colleagues realised that because computers logged on and off P2Ps at a fairly steady rate, they could use these networks as places to store encryption keys temporarily.
