KEY SHARING SYSTEM, SHARED KEY CREATION DEVICE, AND SHARED KEY RESTORATION DEVICE

摘要

Provided is a content distribution system that prevents different keys to be derived between an encryption apparatus and a decryption apparatus. A random-number generating unit 112, in an encryption apparatus 110, generates a random number s. A first function unit 113 generates a functional value G(s) of the random number s, and generates a random-number value u and a shared key K from the functional value G(s). An encryption unit 114 generates a first cipher text c1 of the random number s, using a public-key polynomial h and the random-number value u. A decryption unit 123, in a decryption apparatus 120, decrypts the first cipher text c1 using a secret-key polynomial f, to generate a decryption random number s'. A second function unit 126 generates a functional value G(s') of the decryption random number s', and generates a random-number value u' and a shared key K' from the functional value G(s'). A comparison unit 127 generates a first re-cipher text c1', using the random-number value u' and the shared key K', and outputs the shared key K' if the first cipher text c1 is equal to the first re-cipher text c1'. <IMAGE>