Code access security (CAS) has not been eliminated, Security policy has been eliminated from CAS, but evidence and permissions are still in effect. A few permissions have been eliminated, and transparency has simplified the enforcement of security.We should be aware of the following key points:
- Transparency separates code that runs as part of the application from code that runs as part of the infrastructure. It was introduced in .NET Framework version 2.0, and has been enhanced to become the code access security enforcement mechanism. Unlike security policy, level 2 transparency rules are enforced at run time, not at assembly load time. These rules are always in effect, even for assemblies that run as fully trusted by default. However, level 2 transparency does not affect fully trusted code that is not annotated, such as desktop applications. Assemblies (including desktop assemblies) that are marked with the and that call methods marked with the receive a . You can change this behavior by applying the and setting the property to ; however, you should do this only for backwards compatibility. You must explicitly mark a desktop application as security-transparent to apply transparency restrictions to it.
- Code that calls security policy APIs receives a in addition to compiler warnings at run time. Policy may be re-enabled by using the
configuration element. When policy is enabled, security transparency is still in effect. Security policy is applied at assembly load time and has no effect on transparency, which is enforced by the runtime.
- The obsolete request permissions (, , and ) receive compiler warnings and do not work in the .NET Framework 4, but they do not cause an exception to be thrown. requests cause a to be thrown at run time.
- The security action is not obsolete, but it should not be used for verifying permissions. Instead, use the for types and methods that require full trust, or use the method for types and methods that require individual permissions.
- If your application is built with Visual Studio 2010, you can run it without these changes by specifying a target .NET Framework version that is earlier than the .NET Framework 4 in the Visual Studio project settings. However, you will not be able to use new .NET Framework 4 types and members. You can also specify an earlier version of the .NET Framework by using the
element in the startup settings schema in your application configuration file.
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