MacTech: Introduction to Unix security concepts

Security can only be achieved when you know its basics.
Volume Number: 19 (2003)
Issue Number: 4
by Marcelo Amarante Ferreira Gomes

Why Unix?

By now, most, if not all, MacTech readers know that Mac OS X derives from Unix. It may not be just another Unix, since it is very different from most other unixes in many aspects. But it definitely is Unix. So, if we are to write good software for it, especially if we want that software to be secure, we need to know more than just the basics about the Unix side of Mac OS X.

This is the first article of a series, written with the intent to give you an idea of what computer security really is about, and how to enforce it. We will emphasize the programmer side, hoping to help you write safer applications; but the material in this series will also be of use to system administrators and even power users.

These articles will focus on Mac OS X, since old-timers already know Classic Mac OS, and most newbies are only interested on X. To better explain Mac OS X concepts, though, it is sometimes easier to talk about Unix concepts in general.

There is a lot of historical material in this series of articles. This material is here not only so you can better understand how things evolved and why they are the way they are. It will also to let us learn from the errors of the past and avoid repeating them. You will often see typical attacks crackers used and how security evolved in response to them.

This history-telling approach has the added benefit of passing along a little bit of Unix culture to die-hard Classic Mac OS programmers. In order to write successful Mac OS X software, traditional Unix programmers should learn a bit of Classic Mac OS culture, while traditional Classic Mac OS programmers should have a look into Unix culture. For a discussion on this subject, see (Gomes 2001).

This first article contains no code at all. It will start by defining computer security and then focus on Unix users and groups. You will see how users and groups are implemented in a typical Unix system, how different the Mac OS X implementation is from the typical, and the impact that each of these subjects has on the security of a system.

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