Application restricted media (ARM) is new feature in Silverlight 5 RC that enables content providers to ensure their content under digital rights management (DRM) is consumed only by Silverlight applications they authorize.
This enables experience protection of DRM’d content, which is particularly useful for media that contains revenue-generating ad content.
To enable ARM for an application you must sign your content using an Authenticode x.509 certificate. You can use signtool.exe, which you also use to create a Silverlight trusted application, although the Silverlight application consuming content does not have to be a trusted application. For example, you could a command like the following:
signtool sign /v /f certificateFile.pfx fileToSign
You can also use the signing mechanism in Visual Studio to sign your application. The following image shows the Signing tab in Visual Studio, which you access from Project Properties:
To learn more about DRM content in general, see Digital Rights Management.