RE-ENCRYPTION KEY GENERATION DEVICE, RE-ENCRYPTION DEVICE, ENCRYPTION DEVICE, DECRYPTION DEVICE AND PROGRAM

摘要

A re-encryption key generation device of an embodiment of the present invention performs re-encryption without decrypting encrypted text data obtained with a first public key, and generates a re-encryption key for obtaining re-encrypted text data that can be decrypted with a second secret key. The re-encryption key generation device stores a first secret key corresponding to the first public key and a second re-encryption key generation key that is different from a second public key corresponding to the second secret key. The re-encryption key generation device generates the re-encryption key on the basis of the first secret key, the second re-encryption key generation key and a plurality of random numbers. The second re-encryption key generation key is formed from a plurality of system-specific values and the second secret key. The re-encryption key includes a power index having a numerator part and a denominator part, or a scalar having a numerator part and a denominator part. The numerator part has the form of a linear combination of the second secret key in which utilized are at least one from between the random numbers and a plurality of secret values that determine relationships between the system-specific values. The denominator part comprises the first secret key.