Java Security, 2nd Edition

Chapter 4. The Security Manager

In the next three chapters, we’re going to discuss how the sandbox of a Java application is implemented. The implementation of the sandbox depends on three things:

• The security manager, which provides the mechanism that the Java API uses to see if security-related operations are allowed.

• The access controller, which provides the basis of the default implementation of the security manager.

• The class loader, which encapsulates information about security policies and classes.

We’ll start by examining the security manager. From the perspective of the Java API, there is a security manager that actually is in control of the security policy of an application. The purpose of the security manager is to determine whether particular operations should be permitted or denied. In truth, the purpose of the access controller is really the same: it decides whether access to a critical system resource should be permitted or denied. Hence, the access controller can do everything the security manager can do.

The reason there is both an access controller and a security manager is mainly historical: the access controller is only available in Java 2 and subsequent releases. Before the access controller existed, the security manager relied on its internal logic to determine the security policy that should be in effect, and changing the security policy required changing the security manager itself. Starting with Java 2, the security manager defers these decisions to the ...