A terminal device which belongs to a first domain and a second domain, each domain being a logical group of terminal devices in a data distribution service, the first domain including a plurality of terminals which pass data only between each other and the second domain including a plurality of terminals which pass data only between each other, a domain not permitting transfer of data among terminal devices belonging to different domains, the terminal device comprising: a domain key holding unit operable to hold a first domain key common to the first domain, the first domain key being a content encryption key required in order to utilize digital content and being associated with an identifier for identifying the first domain and being common to the first domain, and to hold a second domain key common to the second domain, the second domain key being a content encryption key required in order to utilize digital content and being associated with an identifier for identifying the second domain and being common to the second domain; a data duplication unit operable to duplicate data shared by the first domain or the second domain so as to generate duplicate data associated with the first domain or the second domain; an encryption unit operable to encrypt the duplicate data so as to generate encrypted duplicate data, using (i) the first domain key in the case where the duplicate data is associated with the first domain, or (ii) the second domain key in the case where the duplicate data is associated with the second domain, a data storage unit operable to associate the duplicate data with the first domain in the case where the data shared by the first domain is duplicated or associate the duplicate data with the second domain in the case where the data shared by the second domain is duplicated, and to store the encrypted duplicate data into a storage medium, a decryption unit operable to decrypt the encrypted duplicate data stored in the storage medium, using the first domain key or the second domain key held by said key holding unit, so as to restore the encrypted duplicate data to the duplicate data, wherein the data shared by each of the first domain and the second domain indicates (i) a content key which is necessary for using a content that is a digital copyrighted work, and (ii) usage rules, and said duplication unit deletes a part of the duplicate data according to the details of the duplicate data, the deleted part indicating the content key in the duplicate data of the data, and said encryption unit encrypts the rest of the deleted duplicate data so as to generate the encrypted duplicate data, said terminal device further comprising a supplement unit operable to (i) communicate with the terminal device belonging to said first and second domains, (ii) store the content key, and (iii) supplement the part deleted by said duplication unit to the data decrypted by said decryption unit. a domain key holding unit operable to hold a first domain key common to the first domain, the first domain key being a content encryption key required in order to utilize digital content and being associated with an identifier for identifying the first domain and being common to the first domain, and to hold a second domain key common to the second domain, the second domain key being a content encryption key required in order to utilize digital content and being associated with an identifier for identifying the second domain and being common to the second domain; a data duplication unit operable to duplicate data shared by the first domain or the second domain so as to generate duplicate data associated with the first domain or the second domain; an encryption unit operable to encrypt the duplicate data so as to generate encrypted duplicate data, using (i) the first domain key in the case where the duplicate data is associated with the first domain, or (ii) the second domain key in the case where the duplicate data is associated with the second domain, a data storage unit operable to associate the duplicate data with the first domain in the case where the data shared by the first domain is duplicated or associate the duplicate data with the second domain in the case where the data shared by the second domain is duplicated, and to store the encrypted duplicate data into a storage medium, a decryption unit operable to decrypt the encrypted duplicate data stored in the storage medium, using the first domain key or the second domain key held by said key holding unit, so as to restore the encrypted duplicate data to the duplicate data, wherein the data shared by each of the first domain and the second domain indicates (i) a content key which is necessary for using a content that is a digital copyrighted work, and (ii) usage rules, and said duplication unit deletes a part of the duplicate data according to the details of the duplicate data, the deleted part indicating the content key in the duplicate data of the data, and said encryption unit encrypts the rest of the deleted duplicate data so as to generate the encrypted duplicate data, said terminal device further comprising a supplement unit operable to (i) communicate with the terminal device belonging to said first and second domains, (ii) store the content key, and (iii) supplement the part deleted by said duplication unit to the data decrypted by said decryption unit.