THE tiny but highly regarded e-mail host Lavabit abruptly pulled the plug on its 400,000 users on August 8th. Edward Snowden, the fugitive American intelligence contractor, was a user. Lavabit's owner, Ladar Levison, said he would rather shut the service down than "become complicit in crimes against the American people" after receiving government instructions that he says he cannot speak about. Before posting the message, he apparently rendered his customers' stored e-mail permanently unreachable, probably by "zeroing" disk drives (using multiple passes to prevent the retrieval of magnetic "ghosts" left behind), permanently destroying the encryption keys necessary to extract archived messages, or both. Shortly afterwards Silent Circle, a firm that offers secured audio, video, messaging and e-mail said that it had killed its own e-mail system, which relied on different technology, even though it hadn't yet been served with legal orders by the government. How do such "secured" e-mail systems work?
