CRYPTOGRAPHIC SYSTEM, MASTER KEY UPDATE APPARATUS, AND NON-TRANSITORY COMPUTER-READABLE RECORDING MEDIUM STORING MASTER KEY UPDATE PROGRAM

摘要

A master key update apparatus (400) acquires a master public key mpk including a basis B and a master secret key msk including a basis B* which is different from the basis B included in the master public key mpk. The master key update apparatus (400) updates the basis B included in the master public key mpk with updating information upk so as to generate a new master public key mpk′, and updates the basis B* included in the master secret key msk with the updating information upk so as to generate a new master secret key msk′.