The following is an excerpt from the book Designing Secure Software: A Guide for Developers by Loren Kohnfelder, Copyright 2022, No Starch Press

“Art is pattern informed by sensibility.” —Herbert Read

Architects have long used design patterns to envision new buildings, an approach just as useful for guiding software design. This chapter excerpt introduces many of the most useful patterns promoting secure design. Several of these patterns derive from ancient wisdom; the trick is knowing how to apply them to software and how they enhance security.

These patterns either mitigate or avoid various security vulnerabilities, forming an important toolbox to address potential threats. Many are simple, but others are harder to understand and best explained by example. Don’t underestimate the simpler ones, as they can be widely applicable and are among the most effective. Still other concepts may be easier to grasp as anti-patterns describing what not to do. I present these patterns in groups based on shared characteristics that you can think of as sections of the toolbox.

When and where to apply these patterns requires judgment. Let necessity and simplicity guide your design decisions. As powerful as these patterns are, don’t overdo it; just as you don’t need seven deadbolts and chains on your doors, you don’t need to apply every possible design pattern to fix a problem. Where several patterns are applicable, choose the best one or two, or maybe more for critical security demands. Overuse can be counterproductive, because the diminishing returns of increased complexity and overhead quickly outweigh additional security gains.