Foreword to Security Engineering by Ross Anderson

By Bruce Schneier
May 2001

In a paper he wrote with Roger Needham , Ross Anderson coined the phrase "programming Satan's computer" to describe the problems faced by computer-security engineers. It's a phrase I've used ever since.

Programming a computer is straightforward: keep hammering away at the problem until the computer does what it's supposed to do. Large application programs and operating systems are a lot more complicated, but the methodology is basically the same. Writing a reliable computer program is much harder, because the program needs to work even in the face of random errors and mistakes: Murphy's computer, if you will. Significant research has gone into reliable software design, and there are many mission-critical software applications that are designed to withstand Murphy.

Writing a secure computer program is another matter entirely. Security involves making sure things work, not in the presence of random faults, but in the face of an intelligent and malicious adversary trying to ensure that things fail in the worst possible way at the worst possible time...again and again. It truly is programming Satan's computer.

Security engineering is different from any other kind of programming. It's a point I made over and over again in my own book, Secrets and Lies. And it's a point Anderson makes in every chapter of this book. And it's why if you're doing any security engineering...if you're even thinking of doing any security engineering, you need to read this book. It's the first, and only, end-to-end modern security design and engineering book ever written.

And it comes just in time. The history of the Internet divides into three waves. The first wave centered around mainframes and terminals. Computers were expensive and rare. The second wave, from about 1992 until now, centered around personal computers, browsers, and a GUI. And the third, starting now, will see the connection of all sorts of devices that are currently in proprietary networks, standalone, and non-computerized. By 2003, there will be more mobile phones connected to the Internet than computers. Within a few years we'll see many of the world's fridges, heart monitors, bus ticket dispensers, burglar alarms, and electricity meters talking IP. Personal computers will be in the minority.

Security engineering, especially in this third wave, requires you to think differently. You need to figure out not how something works, but how something can be made to not work. You have to imagine an intelligent and malicious adversary inside your system (the "Satan" of Satan's computer), constantly trying new ways to subvert it. You have to think like an alien.

As the late great science fiction editor John W. Campbell, said: "An alien thinks as well as a human, but not like a human." Computer security is a lot like that. Ross is one of those rare people who can think like an alien, and then explain that thinking to humans. Have fun reading.

earlier essay: IT Must Be More Vigilant About Security, Survey Shows
later essay: Computer Security Standards Aren't Scoring In The Commercial World
categories: Computer and Information Security
back to Essays and Op Eds

Photo of Bruce Schneier by Per Ervland.

Schneier on Security is a personal website. Opinions expressed are not necessarily those of Co3 Systems, Inc..