CIPHERTEXT DECRYPTION AUTHORITY TRANSFER SYSTEM

PROBLEM TO BE SOLVED: To prevent a master private key of a PKG device (private key generation device) from being restored even when a ciphertext translator is in collusion with a decryption authority transferred person in a ciphertext decryption authority transfer system in which ciphertext of a PKE system can be translated into ciphertext of an IBE system, and ciphertext decryption authority can be transferred between users using only the IBE system. SOLUTION: A ciphertext decryption authority transfer system 1 is a system for achieving decryption authority transfer of ciphertext between a device 10 for a decryption authority transfer person and a device 20 for a decryption authority transferred person. A private key of the IBE system and auxiliary information are generated from the master private key stored in a PKG device 40 that generates the private key, and a translation key is generated on the basis of the auxiliary information, In sharing a content, ciphertext encrypted by the device 10 for the decryption authority transfer person is translated using the translation key by a ciphertext translation device 30, and the translated ciphertext is decrypted using the private key of the IBE system by the device 20 for the decryption authority transferred person. COPYRIGHT: (C)2008,JPO&INPIT