Identification and Authentication

Access controls exist to keep the bad guys out and to keep the good guys honest.
Companies need to ensure that unauthorized access is not allowed and that
authorized users’ cannot make improper modifications. The controls exist in a
variety of forms, from passwords and ID badges to remote access authentication
protocols and security guards. The tricky part is that they must be incorporated
in a layered approach and that each layer needs to be understood, along with its
relationship to the other layers, to ensure that vulnerabilities are not overlooked
or introduced and that different controls do not step on each other’s toes.

Level of Access control

Access control works at a number of levels described in
the following:
1. The access control mechanisms, which the usersees at the application level,
may express a very rich and complex security policy. A modern online business could assign staff to one of dozens of different roles, each of which could
initiate some subset ofseveral hundred possible transactions in the system.
Some of these (such as credit card transactions with customers) might require
online authorization from a third party while others (such as refunds) might
require dual control.

2. The applications may be written on top of middleware,such as a database
management system or bookkeeping package, which enforces a number of
protection properties. For example, bookkeeping software may ensure that a
transaction that debits one ledger for a certain amount must credit another
ledger for the same amount.

3. The middleware will use facilities provided by the underlying operating system. Asthis constructs resources such as files and communications portsfrom
lower-level components, it acquires the responsibility for providing ways to
control access to them.

4. Finally, the operating system access controls will usually rely on hardware
features provided by the processor or by associated memory management
hardware. These control which memory addresses a given process can access.
As we work up from the hardware through the operating system and middleware to
the application layer, the controls become progressively more complex and less reliable. Most actual computer frauds involve staff accidentally discovering features of the
application code that they can exploit in an opportunistic way, or just abusing features
of the application that they were trusted not to. But in this chapter, we will focus on the
fundamentals: access control at the hardware and operating system level. (Applicationlevel controls aren’t different in principle, but I leave detailed discussion to Part 2 of
this book.)

As with the other building blocks discussed so far, access control makes sense only
in the context of a protection goal, typically expressed as a security policy. This puts
us at a slight disadvantage when discussing PCs running single-user operating systems
such as DOS and Win95/98, which have no overt security policy: any process can
modify any data. People do have implicit protection goals, though; you don’t expect a shrink-wrap program to trash your hard disk. So an explicit security policy is a good
idea, especially when products support some features that appear to provide protection,
such as login IDs.
I mention one protection technique—sandboxing—later, but leave off a substantial
discussion of viruses and the like to Section 18.4. In what follows, the focus will be on
protection mechanisms for systems that support the isolation of multiple processes. I
discuss operating system mechanisms first, as it is their requirements that usually drive
hardware protection system design.

What is access Control

There are many type of access control such as :
- access control for computers.
- access control for machine.
- access control for doors.
- access control for area.
An important requirement of any information management system is to protect data
and resources against unauthorized disclosure (secrecy) and unauthorized or improper
modifications (integrity), while at the same time ensuring their availability to legitimate
users (no denials-of-service). Enforcing protection therefore requires that every access
to a system and its resources be controlled and that all and on ly authorized accesses can
take place. This process goes under the name of access control. The development of an
access control system requires the definition of the regulations according to which access is to be controlled and their implementation as functions executable by a computer
system. The development process is usually carried out with a multi-phase approach
based on the following concepts:
Security policy: it defines the (high-level) rules according to which access control
must be regulated.1
Security model: it provides a formal representation of the access control security policy and its working. The formalization allows the proof of properties on the security
provided by the access control system being designed.