There's a fantastic paper Nate showed me that I need to dig up that established some bounds for timing attacks using statistical filtes. Long story short: you can time low microseconds granularity over the Internet, and you can time <i>nanoseconds</i> over a LAN.<p>Memcmp is just on the threshold of Internet-timeable. And that's <i>memcmp</i>, which screams.<p>But Internet-timeable is irrelevant, because anyone who wants to time your app is just going to get an account at the same hosting provider as you and wind up a GigE hop or two away. Hosting on Slicehost, EC2, Linode, or GAE? That step took 5 minutes and $20. I'd pay $20 to bust up an app I hadn't even heard of, let alone a popular app.