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

This book is a guide for software professionals who want to better understand concepts essential to the discipline of software security and learn how to practice the art of secure software design and implementation. Several of the topics covered here I was fortunate to have innovated myself. Others, I witnessed develop and take root. Based on my own industry experience, this book is packed with actionable ideas you can start using right away to contribute to securing the software you work on.

Two central themes run through this book: encouraging software professionals to focus on security early in the software construction process, and involving the entire team in the process of—as well as the responsibility for—security. There is certainly plenty of room for improvement in both of these areas, and this book shows how to realize these goals.

I have had the unique opportunity of working on the front lines of software security over the course of my career, and now I would like to share my learnings as broadly as possible. Over 20 years ago, I was part of the team at Microsoft that first applied threat modeling at scale across a large software company. Years later, at Google, I participated in an evolution of the same fundamental practice, and experienced a whole new way of approaching the challenge. Part 2 of this book is informed by my having performed well over a hundred design reviews. Looking back on how far we have come provides me with a great perspective with which to explain it all anew.

Designing, building, and operating software systems is an inherently risky undertaking. Every choice, every step of the way, nudges the risk of introducing a security vulnerability either up or down. This book covers what I know best, learned from personal experience. I convey the security mindset from first principles and show how to bake in security throughout the development process. Along the way I provide examples of design and code, largely independent of specific technologies so as to be as broadly applicable as possible. The text is peppered with numerous stories, analogies, and examples to add spice and communicate abstract ideas as effectively as possible.

The security mindset comes more easily to some people than others, so I have focused on building that intuition, to help you think in new ways that will facilitate a software security perspective in your work. And I should add that in my own experience, even for those of us to whom it comes easily, there are always more insights to gain.

This is a concise book that covers a lot of ground, and in writing it, I have come to see this as essential to what success it may achieve. Software security is a field of intimidating breadth and depth, so keeping the book shorter will, I hope, make it more broadly approachable. My aim is to get you thinking about security in new ways, and to make it easy for you to apply this new perspective in your own work.

Who Should Read This Book?

This book is for anyone already proficient in some facet of software design and development, including architects, UX/UI designers, program managers, software engineers, programmers, testers, and management. Tech professionals should have no trouble following the conceptual material so long as they understand the basics of how software works and how it’s constructed. Software is used so pervasively and is of such great diversity that I won’t say that all of it needs security; however, most of it likely does, and certainly any that connects to the internet or interfaces significantly with people.

In writing the book, I found it useful to consider three classes of prospective readers, and would like to offer a few words here to each of these camps.

  • Security newbies, especially those intimidated by security, are the primary audience I am writing for, because it’s important that everyone working in software understand security so they can contribute to improving it. To make more secure software in the future we need everyone involved, and I hope this book will help those just starting to learn about security to quickly get up to speed.

  • Security-aware readers are those with interest in but limited knowledge of security, who are seeking to round out and deepen their understanding and also learn more practical ways of applying these skills to their work. I wrote this book to fill in the gaps, and provide plenty of ways you can immediately put what you learn here into practice.

  • Security experts (you know who you are) round out the field. They may be familiar with much of the material, but I believe this book provides some new perspectives and still has much to offer them. Namely, the book includes discussions of important relevant topics, such as secure design, security reviews, and “soft skills” that are rarely written about.

NOTE The third part of this book, which covers implementation vulnerabilities and mitigations, includes short excerpts of code written in either C or Python. Some examples assume familiarity with the concept of memory allocation, as well as an understanding of integer and floating-point types, including binary arithmetic. In a few places I use mathematical formulae, but nothing more than modulo and exponential arithmetic. Readers who find the code or math too technical or irrelevant should feel free to skip over these sections without fear of losing the thread of the overall narrative. References such as man(1) are *nix (Unix family of operating systems) commands (1) and functions (3).