I'm not sure if it's computationally possible with current technology, but it is at least theoretically possible (I think) to encrypt every step in the message so that not only could the gov't or national enquirer not read your messages to your wife, but they could not even know that you were talking to her.

You would essentially TRACERT your wife, get the list of computers between the two, and encrypt the message successively with a key belonging to each computer/router in the chain. Thus, you encrypt the message with your ISP's key, and send the message to it. Your ISP decrypts the message, and gets the next step in the chain -- an intermediate router between you and your wife's computer -- and passes along the message, now encrypted with the intermediate router's key. It would turn your communications into a kind of scavenger hunt, wherein each successive recipient only knows who gave it the message and to whom it must give the message next, and nothing about its contents or the ultimate source or destination.

Properly done, the government/evil corporation X/boogeyman wouldn't even know which messages to capture for cryptanalysis. Of course, if they had somehow previously identified you as a Very Dangerous Person, they could tap your lines and collect all your communications and submit them to their underground city of supercomputers in Columbia, Maryland for eventual decryption. However, the list of VDPs would have to be a short one, given the computational resource constraints. They would hopefully have room, say, for Saudi nationals who had taken 100 hours of flying lessons but had indicated that they had no need to learn how to land a plane, but they would probably not have room for everyone who was arrested at the RNC protests in New York in 2004, or everyone who had ever written an inflammatory internet post about abortion doctors or purchased pornography with a credit card.

-- HarryLayman - 05 Nov 2009