Should a lock or a key icon be used to indicate exclusive content?

I'm in the process of designing an icon which will indicate that certain content is exclusive/premium. To provide more context, a user will not be able to access this content (content being a video or article) unless they have signed into the application first.

The icon will appear on top of a content card to indicate that the content is exclusive

In terms of the icon, would it be better to use a lock icon or a key icon?