Patent ID: 7630940

Claim:
A content sharing system comprising: a first device comprising: (i) a receiver which receives, from a server, encrypted content which is encrypted by using a content key and a right object, associated with the encrypted content, wherein the right object includes at least an encrypted content key generated by encrypting the content key with a key encryption key, an encrypted key encryption key generated by encrypting the key encryption key with a public key, and first right information which defines a range of playing the encrypted content, enabling the first device to play the encrypted content; (ii) a storage unit which stores the encrypted content and the right object received from the server; (iii) a session key generating unit which generates a session key by executing a mutual authentication with a second device; (iv) an encryption/decryption unit which decrypts the encrypted key encryption key with a secret key of the first device and re-encrypts the decoded key encryption key with the session key; and (v) a transmitter which transmits the encrypted content encrypted with the content key, the encrypted content key encrypted with the key encryption key, the encrypted key encryption key encrypted with the session key, and second right information, which is a part of the first right information, to a second device; and wherein the second device comprises: (i) a receiver which receives the encrypted content encrypted with the content key, the encrypted content key encrypted with the key encryption key, the encrypted key encryption key encrypted with the session key, and the second right information which is a part of the first right information from the first device; and (ii) a storage unit which stores the encrypted content encrypted with the content key, the encrypted content key encrypted with the key encryption key, the encrypted key encryption key encrypted with the session key, and the second right information which is a part of the first right information.