Security and Usability

Chapter One. Psychological Acceptability Revisited

Matt Bishop

IN 1987, BRIAN REID WROTE “PROGRAMMER CONVENIENCE IS THE ANTITHESIS OF SECURITY, because it is going to become intruder convenience if the programmer’s account is ever compromised.”^[*] This belief of the fundamental conflict between strong computer security mechanisms and usable computer systems pervades much of modern computing. According to this belief, in order to be secure, a computer system must employ security mechanisms that are sophisticated and complex—and therefore difficult to use.

Today a growing number of security researchers and practitioners realize that this belief contains an inherent contradiction. The reason has to do with the unanticipated result of increasing complexity. A fundamental precept of designing security mechanisms is that, as the mechanisms grow more complex, they become harder to configure, to manage, to maintain, and indeed even to implement correctly. Errors become more probable, thereby increasing the chances that mechanisms will be configured erroneously, mismanaged, maintained improperly, or implemented incorrectly. This weakens the security of the system. So the more complex a system is, the more secure it should be—yet the less secure it is likely to be, because of the complexity designed to add security!

Finding ways to maximize both the usability of a system and the security of a system has been a longstanding problem. Saltzer and Schroeder’s principle of psychological acceptability ...