A method for joining a user domain based on digital right management (DRM), a method for exchanging information between a user device and a domain enforcement agent, and a method for exchanging information between user devices belonging to the same user domain include sharing a domain session key between the user device and the domain enforcement agent or between the user devices belonging to the same user domain. Information is exchanged through a secure session set up between the user device and domain enforcement agent or between the user devices, and information exchange occurs through encryption/decryption using the domain session key.