Code Access Security

1. Code Access Security Ami Dudu Software architect IDF xdim@netvision.net.il

2. Agenda • Goals • Evidence-Based security • Security policy • Permission classes • Role-based Security • Common Interfaces\BaseClasses • Implementing your own classes

3. Goals • Ensures that code can access only resources it has the right to access • Allows security policy to control the resource code has access to based on: • Where the code comes from • Other aspects of the code’s identity • Allows programmers to specify resources that their code • Must be able to access in order to run effectively • Could optionally access • Should not be able to access

4. Possibilities • Secure our libraries • Defend our servers more effectively • Writing application using RBS • And more…

5. Evidence-Based security • Set of information about the identity and origin of an assembly • Uses by the .Net Framework security system at load time to determine the permissions an assembly receives • Evidence includes things such as Strong-Name, Signature, Code Location, Zone and can also be custom-defined

6. Security policy • Storage of the security permissions • Policy levels: enterprise, machine, user • Each level consists of a collection of hierarchical code groups, and each code group has a set of permissions (file system, registry, environment variables etc.) • Final Permission set is union for same level and intersection between levels

7. Security Policy

8. C:\foo.dll SN=0x00.. Hash=00.. Calc. level permission All Code Nothing Nothing Zone=My Computer Full trust Zone=Local Intranet IO Permission SN=0xD1… Full trust Full trust Hash=01… Events Permission Hash=04… UI Permission Hash=00… Events Permission Union Full trust

9. http://www SN=0xD1.. Hash=00.. Calc. level permission All Code Nothing Nothing Zone=My Computer Full trust Zone=Local Intranet IO Permission SN=0xD1… Full trust Full trust Hash=01… Events Permission Hash=04… UI Permission Hash=00… Events Permission Events Permission Union Full trust

10. Calc. level permission C:\foo.dll SN=0xD1.. Hash=01.. All Code Nothing Nothing Zone=My Computer Full trust Zone=Local Intranet IO Permission SN=0xD1… Full trust Full trust Full trust Hash=01… Events Permission Hash=04… UI Permission Hash=00… Events Permission Union Full trust

11. Playing with rights

12. Permissions • Permissions represent the right to interact with a given resource • Examples: FileIO Registry Environment Socket Reflection Directory Services Printing SQLClient Message Queue Event Log DNS And more…

13. Declarative Demands • Specify security check using attributes • Permission state must be known at compile time • Can be viewed with PermView SDK Tool or Ildasm [FileIOPermission(SecurityAction.Demand, Write = @"C:\Temp")] private void TryToCreateAFile() { // create a file }

14. SecurityAction Enum • Demand – All callers higher in the call stack are required to have been granted the permission specified by the current permission object • LinkDemand – The immediate caller is required to have been granted the specified permission • Assert – The calling code can access the resource identified by the current permission object, even if callers higher in the stack have not been granted permission to access the resource • And More…

15. Imperative Demands • Allows security checks to vary by control flow or method state private void foo(string FilePath, string FileName) { FileIOPermission filePerm = new FileIOPermission(FileIOPermissionAccess.Write, FilePath); filePerm.Demand(); // rest of the method }

16. Permission classes methods • Demand • Union • Intersect • Assert • RevertAssert • And more…

17. Work with permissions

18. Role-based security • Role-Based security allows access to code and resources based on: • The user’s Identity • The roles or groups to which the user belong • Role-Based security based on Principals and Identities classes

19. Role-based security • Identity information typically consists of the user name and the roles associated with the user • In .Net Framework identity encapsulates the user’s login name, and the principal encapsulates the user’s role membership information • .Net framework supports identity and principal for the Microsoft Windows user and group information, or custom identity and principal

20. Role-based security

21. Common Interfaces\BaseClasses • ISecurityEncodable • FromXML, ToXML (SecurityElement) • IPermission • Copy, Demand, Intersect, IsSubsetOf, Union • IUnrestricted • IsUnrestriced • CodeAccessPermission as BaseClass • PemitOnly, Deny, RevertXXX

22. Implementing your own classes

23. Possibilities • Secure our libraries • Defend our servers more effectively • Writing application using RBS • And more…

24. Questions ?