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

摘要

There is provided a content distribution system preventing derivation of different keys between an encryption device and a decryption device. The encryption device (110d) includes: a random number generation section (112d) for generation a random number s; a first function section (113d) for generation a function value G(s) of the random number s and generating an authentication value a and a shared key K from the function value G(s); an encryption section (114d) for generating a first encrypted text c1 of the authentication value a by using a public key polynominal h; a second function section (115d) for generating a function value H(a, c1) of the authentication value a and the first encrypted text c1; and a random number mask section (116d) for generating a second encrypted text c2 = s xor H(a, c1). The decryption device (120d) includes: a decryption section (123d) for decrypting the first encrypted text c1 by using a secret key polynominal f and generating a decrypted authentication value a'; a third function section (124d) for generating a function value H(a', c1) of the authentication value a' and the first encrypted text c1; a random number mask removal section (125d) for generating a decrypted random number s' = c2 xor H(a', c1); a fourth function section (126d) for generating a Hush function value G(s') of the decrypted random number s' and generating an authentication value a" and a shared key K' from the function value G(s'); and a comparison section (127d) for outputting the shared key K' if the decrypted authentication value a' is equal to the authentication value a".