http://www.linuxsecurity.com/articles/cryptography_article-4356.html
A Brief Comparison of Email Encryption Protocols
Raph Levien
Posted By: Jen Olson
1/30/2002 14:31
Update: Shaun Gordon pointed out this article is quite old, and while not
current still contains useful info. This
--
Jei, quoting an old but still too true document
An additional grave concern is key management. Contrary
to some beliefs,key management is not a solved problem.
All of the proposals contain some mechanism for key
management, but none of them have been demonstrated to be
scalable
