Page 1126 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

tasks. The primary purpose is to keep secret information secret. If you
want to keep a secret, the best way is to tell no one. If you’re the only

person who knows it, you can ensure that it remains a secret. If you
tell a trusted friend, it might remain secret. Your trusted friend might
tell someone else—such as another trusted friend. However, the risk of
the secret leaking out to others increases as more and more people
learn it. Limit the people who know and you increase the chances of
keeping it secret.

Need-to-know is commonly associated with security clearances, such
as a person having a Secret clearance. However, the clearance doesn’t
automatically grant access to the data. As an example, imagine that
Sally has a Secret clearance. This indicates that she is cleared to access
Secret data. However, the clearance doesn’t automatically grant her
access to all Secret data. Instead, administrators grant her access to
only the Secret data she has a need-to-know for her job.

Although need-to-know is most often associated with clearances used
in military and government agencies, it can also apply in civilian
organizations. For example, database administrators may need access
to a database server to perform maintenance, but they don’t need
access to all the data within the server’s databases. Restricting access
based on a need-to-know helps protect against unauthorized access
resulting in a loss of confidentiality.

The Principle of Least Privilege

The principle of least privilege states that subjects are granted only
the privileges necessary to perform assigned work tasks and no more.
Keep in mind that privilege in this context includes both permissions
to data and rights to perform tasks on systems. For data, it includes
controlling the ability to write, create, alter, or delete data. Limiting
and controlling privileges based on this concept protects
confidentiality and data integrity. If users can modify only those data

files that their work tasks require them to modify, then it protects the
integrity of other files in the environment.

The principle of least privilege relies on the assumption