System.Security.Permissions namespace

1. System.Security.Permissions namespace By Venkata Krishna Date: Instructor 06/19/2007 Dr. Ravi Mukkamala

2. Overview • Introduction • Classes in System.Security.Permissions Namespace • Permissions • Code access security • References

3. Introduction • Permissions are the mechanism through which the .NET runtime enforces code-access security. • The System.Security.Permissions namespace contains permission classes and their attributes.

4. Classes in System.Security.Permissions Namespace There are a lot of classes and enumerations in this namespace. Few of the important classes are Classes EnvironmentPermission FileDialogPermission FileIOPermission IsolatedStorageFilePermission IsolatedStoragePermission ReflectionPermission RegistryPermission SecurityPermission UIPermission • Each of these classes have many methods.

5. Permissions There are three distinct categories of permissions defined in the System.Security.Permissions namespace: • Code-Access Permissions, • Identity Permissions and • Role-based Permissions Code-Access Permissions: The Common Language Runtime (CLR) allows code to perform only those operations that the code has permission to perform. • Restrict what your code can do • Restrict which code can call your code • Identify code

6. Identity Permissions: The identity permission classes represent the value of host evidence that an assembly or application domain presents to the runtime. Role-based Permissions: Permissions based on roles of a user on whose behalf code is running.

7. Code access security The elements of CAS are • permissions • permission sets • code groups • evidence • policy

8. Demo Creating permission sets and code groups

9. Two different kinds of syntax when coding security are • Declarative Declarative syntax uses attributes to mark the method, class or the assembly with the necessary security information. [FileIOPermission(SecurityAction.Demand, Unrestricted=true)] public calss MyClass { public MyClass() {...} // all these methods public void MyMethod_A() {...} // demands unrestricted access to public void MyMethod_B() {...} // the file system } • Imperative Imperative syntax uses runtime method calls to create new instances of security classes. public calss MyClass { public MyClass() { } public void Method_A() { // Do Something FileIOPermission myPerm = new FileIOPermission(PermissionState.Unrestricted); myPerm.Demand(); // rest of the code won't get executed if this failed // Do Something } // No demands public void Method_B() { // Do Something } }

10. Requesting Permissions An assembly can request permissions before it is loaded. • RequestMinimum The code will be only allowed to run if all the required permissions are granted by the security policy. [assembly:RegistryPermission(SecurityAction.RequestMinimum, Write="HKEY_LOCAL_MACHINE\\Software")] • RequestOptional Permissions that the code can use, but not required in order to run. [assembly:FileIOPermission(SecurityAction.RequestOptional, Write="C:\\")] • RequestRefuse To specify the permissions that the assembly would never require. [assembly:FileIOPermission(SecurityAction.RequestRefuse, Write="C:\\")]

11. Overriding Security An assembly can override the permissions in three ways. • Assert Assert method to stop the stack walk from going beyond the current stack frame. FileIOPermission myPerm = new FileIOPermission(FileIOPermissionAccess.Read, "C:\\"); myPerm.Assert(); // don't check above stack frames. • Deny Deny the current set of permissions. WebPermission myWebPermission = new WebPermission(NetworkAccess.Connect, "http://www.somewebsite.com"); myWebPermission.Deny(); • PermitOnly PermitOnly in some situations when needed to restrict permissions granted by security policy. WebPermission myWebPermission = new WebPermission(NetworkAccess.Connect, "http://www.somewebsite.com"); myWebPermission.PermitOnly();

12. References • O’Reilly : Programming .NET Security By Adam Freeman, Allen Jones , June ’03 • http://msdn2.microsoft.com/en-us/library/system.security.permissions.aspx • http://www.codeproject.com/dotnet/UB_CAS_NET.asp

13. Discussion