127Chapter 5 CHAPTER 5
Security 5
Given a choice between dancing pigs and security,
users will pick dancing pigs every time.
—Ed Felten and Gary McGrawSecurity issues are often overlooked on smaller sites or low-traffic applications;
unfortunately, the reach of the Web has expanded to a point where end-to-end secu-
rity is essential on any public-facing web site. There actually are people with nothing
better to do than run a distributed denial-of-service attack on “Aunt Edna’s Funny
Cat Pictures.” Nobody can afford to ignore the dangers that face a site simply as a
consequence of being accessible on the Internet.
In this chapter, we will take a top-down approach to examining the various security-
related issues that plague web application developers. We start by examining the
architectural, application-level principles you should keep in mind. Later, we will get
progressively more detailed. We will examine the security-related issues you should
keep in mind when working at a lower level in Rails.
Application Issues
First, we will examine some important principles that should guide the design of any
web application.
Authentication
The most important guideline in the area of authentication is simple:
Always salt and hash all passwords!There are very few valid exceptions to this rule, and even fewer apply to web applica-
tions. The only possible reason to store passwords in plain text is if they must be pro-
vided to an external service in plain text. Even then, the passwords should be
symmetrically encrypted with a shared secret, to provide defense in depth.