Two of the many well-known CAs on the Internet are VeriSign (http://www.verisign.com) and Thawte (http://www.thawte.com). You may find it useful to look at their Web sites from time to time while reading this chapter.
At this point we need to introduce the term "entity". A user of a network or intranet or the Internet might not be an individual person - it could be an organization, or even a machine. So we'll use the more general term "entity" from now on.