| 摘要 |
PROBLEM TO BE SOLVED: To provide a key updating method capable of updating the decryption key of a user without performing communication with another person in an encryption system based on an ID; and to provide an encryption system, an encryption server, a terminal device and an external device. SOLUTION: This center server 100 is used in an encryption system using an identifier unique to a user as a public key. The center server 100 is provided with a master key selecting section 109 for selecting a master key on the basis of a hierarchical algorithm (HIBE) for forming the generation of the decryption key corresponding to the public key into hierarchy, a public information generator 107 for operating and generating public information to be disclosed to the predetermined group on the basis of the master key and HIBE, an updating key generator 103 for generating an updating key used for update of the decryption key corresponding to the identifier on the basis of HIBE by using the master key and the public information, and a decryption key generator 105 for generating a decryption key on the basis of HIBE by using the master key and the identifier. COPYRIGHT: (C)2005,JPO&NCIPI
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