Shared Source CLI Essentials

Securing Against Harmful Assemblies

The SSCLI supports Code Access Security (CAS) , which is a component-aware approach to security that extends traditional OS security concepts. The goal for the SSCLI is to provide a level playing field for the components themselves, to enable code from many sources to be combined into applications. Since programs run under the control of the execution engine, and since component code is verified when it is JIT compiled, it is possible for the CLI execution engine to intervene when components misbehave. Because this is possible, the runtime enforcement mechanisms of code access security have real teeth. They would not be possible without managed execution as their foundation.

Code access security combines permissions with evidence and policy. There are two parts to CAS: the assembly load phase and the runtime enforcement phase. We will talk briefly about the load phase at this point and defer the discussion of how runtime enforcement is achieved until Chapter 6.

Permissions represent specific capabilities, such as the ability to read a file. Permissions are used in permission grants and permission demands , which are runtime actions that are tracked and enforced by the CAS service within the execution engine. A permission grant (henceforth referred to as just a “grant”) is an authorization based on some combination of policy and evidence; a demand is a check for the corresponding grant.

Within an assembly, permissions may be associated with resources, ...