In our whiteboard example, we've assumed that you have control over both the client-side and server-side installations. In other configurations, this isn't the case. For example, Web servers can be used with just about any Web browser, and the people who install the Web server software have nothing to do with those who install browser software. For this reason, Web servers and other public-protocol servers use third-party certification authorities to provide key certificates.

Instruction for using these systems is beyond the scope of this tutorial, but each one generally provides its own detailed instructions. In many cases, you can request a free certificate which can be used for testing purposes -- this lets you "try before you buy." See Resources for links to third-party certification authorities.