Mechanisms are disclosed that allow for execution of unsigned content and the securing of resources in a closed system when such unsigned content is executing on the system. For example, an application programming interface is used between an access layer implementing unsigned content and an operating system of the closed system. The application programming interface may have sub-interfaces that correspond to sub-layers of the access layer, including a graphics sub-interface, an audio sub-interface, an input sub-interface, and a storage sub-interface. These sub-interfaces present access calls made by the sub-layers to the protected resources of the closed system. By providing the application programming interface, unsigned content, e.g., video games can run on a closed system that is typically designed to run only signed content.