I'd assume there's some chance that the person will screw up - even a little. The NSA is very good at exploiting very small mistakes. In the Venona project, ht

I'd assume there's some chance that the person will screw up - even a little. The NSA is very good at exploiting very small mistakes. In the Venona project, http://en.wikipedia.org/wiki/Venona http://en.wikipedia.org/wiki/Venona, they NSA realized that the soviets were re-using one time pads. By knowing A xor C and B xor C, they were able to get A xor B - and from that, they were able to decode the messages. I could imagine things like looking at the tor traffic, and trying to match up things like writing patterns. And of course, there's the very good chance some people aren't using tor right. I don't think that what the NSA is doing is legal - but think there's a good chance it's somewhat effective.