Secure E-Mail C. Ellison and B. Schneier Inside Risks 115, Communications of the ACM, vol 43, n 1, Jan 2000.
Certificates provide an attractive business model.
They cost almost nothing to manufacture, and you can dream of selling one a year to everyone on the Internet. Given that much potential income for CAs, we now see many commercial CAs, producing literature, press briefings and lobbying. For e-mail, you want to establish whether a given keyholder is the person you think or want it to be. When you verify signed e-mail, you hope to establish who sent the message. When you encrypt e-mail to a public key, you need to know who will be capable of reading it.