For more information, see the following resources:
"Security in .NET: The Security Infrastructure of the CLR Provides Evidence, Policy, Permissions, and Enforcement Services" in MSDN Magazine at http://msdn.microsoft.com/msdnmag/issues/02/09/SecurityinNET/default.aspx .
"Security in .NET: Enforce Code Access Rights with the Common Language Runtime" in MSDN Magazine at http://msdn.microsoft.com/msdnmag/issues/01/02/CAS/default.aspx .
LaMacchia, Lange, Lyons, Martin, and Price. .NET Framework Security . Addison Wesley Professional, 2002.
"How To: Create a Custom Encryption Permission" in the "How To" section of this guide.