ENCRYPTION SYSTEM, KEY GENERATING DEVICE, RE-ENCRYPTION DEVICE, AND USER TERMINAL

摘要

This encryption system (10) uses an encryption protocol which, when two instances of information mutually correspond, is capable of decrypting an encrypted text, whereupon one of the instances of information is set, with a decryption key whereupon the other of the instances of information is set. A key generating device (401) generates a user secret key whereupon is set one of mutually corresponding instances of key information (u, y), and a re-encryption key which converts an encrypted text which may be decrypted with an attribute secret key whereupon is set one of mutually corresponding instances of user attribute information (x, v) to a re-encrypted text whereupon the other instance of key information (u, y) is set. An encrypted text storage device (201) stores the encrypted text whereupon the other instance of user attribute information (x, v) is set. A re-encryption device (301) re-encrypts with the re-encryption key the encrypted text which the encrypted text storage device stores and generates a re-encrypted text. A user terminal (601) decrypts the re-encrypted text with the user secret key.