In order to implement SSL, a web server must have an associated Certificate for each external interface (IP address) that accepts secure connections. The theory behind this design is that a server should provide some kind of reasonable assurance that its owner is who you think it is, particularly before receiving any sensitive information. While a broader explanation of Certificates is beyond the scope of this document, think of a Certificate as a “digital driver’s license” for an Internet address. It states what company the site is associated with, along with some basic contact information about the site owner or administrator.
This “driver’s license” is cryptographically signed by its owner, and is therefore extremely difficult for anyone else to forge. For sites involved in e-commerce, or any other business transaction in which authentication of identity is important, a Certificate is typically purchased from a well-known Certificate Authority (CA) such as VeriSign or Thawte. Such certificates can be electronically verified — in effect, the Certificate Authority will vouch for the authenticity of the certificates that it grants, so you can believe that that Certificate is valid if you trust the Certificate Authority that granted it.
In many cases, however, authentication is not really a concern. An administrator may simply want to ensure that the data being transmitted and received by the server is private and cannot be snooped by anyone who may be eavesdropping on the connection. Fortunately, Java provides a relatively simple command-line tool, called keytool, which can easily create a “self-signed” Certificate. Self-signed Certificates are simply user generated Certificates which have not been officially registered with any well-known CA, and are therefore not really guaranteed to be authentic at all. Again, this may or may not even be important, depending on your needs.
