Key generation device, key derivation device, encryption device, decryption device, method and program

摘要

A key generation device (900) receives therein a public key (901) including a hierarchical element (902), a master key (903) including a secret hierarchical element (911), an identity &thetas; (904), and a random number (905). The key generation device (900) generates two random number elements (906a, 906b) from the random number (905), and generates a secret key (908) including an element obtained by raising the secret hierarchical element (911) to a power of the two random numbers.