Improving Web Application Security: Threats and - CGISecurity

Chapter 14: Building Secure Data Access 375Use Separate Data Access AssembliesIf you have a choice, avoid placing data access logic directly in ASP.NET pages or incode-behind files. There are security, reuse, and maintenance advantages to placingdata access logic in a separate assembly and implementing a logical data access layerthat is separate from your application business and presentation logic.From a security perspective, you can:● Use a strong name for the assembly, which provides tamperproofing.● Use sandboxing to isolate your data access code, which is important if your codeneeds to support partial-trust callers — for example, partial-trust Web applications.● Use data access methods and classes that authorize calling code using codeidentity permission demands.For defense in depth, perform principal-based authorization using principalpermission demands in your business components and use code identity permissiondemands to authorize the code that calls your data access logic, as shown inFigure 14.2.Principal-BasedAuthorizationThe caller is authorizedbased on rolemembershipCode Identity-BasedAuthorizationThe calling code isauthorized based onidentity evidenceWeb AppBusinessClassesDataAccessClassesAssembly1 Assembly2 Assembly3Presentation Business DataFigure 14.2Separation of presentation, business, and data access layersFor more information about authorization for data access code, see the“Authorization” section, later in this chapter.