http://www.iykpqm7jiradoeezzkhj7c4b33g4hbgfwelht2evxxeicbpjy44c7ead.onion/deeplinks/2012/03/https-and-tor-working-together-protect-your-privacy-and-security-online
Finally, government agencies with particularly vast resources, such as the NSA, may be able to circumvent the protection provided by Tor through what is known as the “Global Network Adversary” attack. If the Global Network Adversary (GNA) controls the relay through which you enter the Tor network and the relay through which you exit, the GNA can correlate the size and timing of your traffic to identify you on the Tor network.