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This chapter is from the book

On Art and Engineering

Software that is properly engineered goes through a well-structured process from requirements design, through detailed specification, to actual implementation. In the world of consumer-ware (software created for the mass consumer market, like browsers), pressure to be first to market and retain what is known as "mind share" compresses the development process so much that software engineering methods are often thrown out the window. This is especially true of testing, which regularly ends up with no scheduled time and few resources. An all-too-common approach is to leave rigorous testing to users in the field (sometimes even paying users when they find bugs!). We think this is just awful.

The Internet time phenomenon has exacerbated the software engineering problem. These days, Internet years rival dog years in shortness of duration. Given the compressed development schedules that go along with this accelerated kind of calendar, the fact that specifications are often very poorly written (if they exist at all) is not surprising. It is not uncommon to encounter popular consumer-oriented systems that have no specifications.

Java makes a good case study of the complex interrelation between secure design and secure implementation. One of the most common misconceptions about Java security holes is that they are all simple implementation errors and that the specification has been sound and complete since day one. Threads in the newsgroup comp.lang.java.security and other newsgroups often repeat this fallacy as people attempt to trivialize Java's security holes. The truth is that many of the holes described in books like Securing Java are simple implementation bugs (the code-signing hole from April 1997 comes to mind), but others, like problems discovered in Java class loaders, are not [McGraw, 1999]. Sometimes the specification is just plain wrong and must be changed. As an example, consider the Java specification for class loading, which has evolved as inadequacies have come to light. In any case, the much-hyped Java security model focuses primarily on protecting against malicious mobile code. Java is still susceptible to a large number of the same problems as other languages.

Often it is hard to determine whether a security hole is an implementation problem or a specification problem. Specifications are notoriously vague. Given a vague specification, who is to blame when a poor implementation decision is made? Specifications are also often silent; that is, when a hole is discovered and the specification is consulted, there is nothing said about the specific problem area. These sorts of omissions certainly lead to security problems, but are the resulting problems specification problems or implementation problems? In the end, the holes are fixed, regardless of whether they are implementation bugs or design-level problems. This leads to a more robust system. Of course, designing, implementing, and testing things properly in the first place is the least expensive and most successful approach. We discuss how to use software engineering to do these things in Chapter 2.

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