Security Engineering, 3rd Edition

CHAPTER 6Access Control

Anything your computer can do for you it can potentially do for someone else.

– ALAN COX

Microsoft could have incorporated effective security measures as standard, but good sense prevailed. Security systems have a nasty habit of backfiring and there is no doubt they would cause enormous problems.

– RICK MAYBURY

6.1 Introduction

I first learned to program on an IBM mainframe whose input was punched cards and whose output was a printer. You queued up with a deck of cards, ran the job, and went away with printout. All security was physical. Then along came machines that would run more than one program at once, and the protection problem of preventing one program from interfering with another. You don't want a virus to steal the passwords from your browser, or patch a banking application so as to steal your money. And many reliability problems stem from applications misunderstanding each other, or fighting with each other. But it's tricky to separate applications when the customer wants them to share data. It would make phishing much harder if your email client and browser ran on separate machines, so you were unable to just click on URLs in emails, but that would make life too hard.

From the 1970s, access control became the centre of gravity of computer security. It's where security engineering meets computer science. Its function is to control which principals (persons, processes, machines, …) have access to which resources in the system – which ...