This paper is very popular / influential in the area of usable security. It's interesting to note that though it's possible to securely exchange e-mail, most people don't. I took a course offered by Prof. Tygar (co-author of the paper) last year and we evaluated how easy it is to send encrypted mail using Thunderbird+Enigmail+GnuPG. While the usability of the software has improved in the 10 years since the paper was written, it is nowhere near the level required to make this a mainstream technology. Maybe it is inherent to the process itself. I don't see how you can simplify key exchange to make it very easy for the average user. I guess the price you pay for security is to go through the pain of figuring out how it works. Of course, most people will not / cannot do that even if it is in their best interest.

I'd loved to hear the thoughts of the security gurus on HN about this...