Chapter 4. SSL and TLS
Like many other Internet protocols created before it, HTTP was designed under the assumption that data transmission would be secure. This is a perfectly valid assumption; it makes sense to put a separate communication layer in place to worry about issues such as confidentiality and data integrity. Unfortunately, a solution to secure data transmission was not offered at the same time as HTTP. It arrived years later, initially as a proprietary protocol.
By today's standards, the Internet was not a very secure place in the early days. It took us many years to put mechanisms in place for secure communication. Even today, millions of users are using insecure, plaintext communication protocols to transmit valuable, private, and confidential information.
Since these are serious problems, the only cases where additional security measures are not required are with a web site where all areas are open to the public or with a web site that does not contain any information worth protecting. Some cases require protection:
To secure HTTP, the Secure Sockets Layer (SSL) protocol is used. This chapter begins by covering cryptography from a practical point of view. You only need to understand the basic principles. We do not need to go into mathematical details and discuss differences between algorithms for most real-life requirements. After documenting various types of encryption, this chapter will introduce SSL and describe how to use the OpenSSL libraries and the mod_ssl Apache module. Adding SSL capabilities to the web server is easy, but getting the certificate infrastructure right requires more work. The end of the chapter discusses the impact of SSL on performance and explains how to determine if SSL will represent a bottleneck.