US 2004/0174997 A1 · Key agreement system, shared-key generation apparatus, and shared-key recovery apparatus

Abstract

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′.

Claims43

Dependent claims

A key agreement system comprising a shared-key generation apparatus and a shared-key recovery apparatus, each apparatus establishing therein a same shared key in secrecy, wherein

the shared-key generation apparatus includes:
a seed-value generating unit operable to generate a seed value;
a first shared-key generating unit operable to generate a blind value and a shared key, from the seed value;
an encryption unit operable to encrypt the seed value based on the blind value, to generate encryption information;
and
a transmitting unit operable to transmit the encryption information, and
the shared-key recovery apparatus includes:
a receiving unit operable to receive the encryption information;
a decryption unit operable to decrypt the encryption information, to generate a decryption seed value;
a second shared-key generating unit operable to generate a decryption blind value and a decryption shared key, using the decryption seed value and according to a same method as used in the first shared-key generating unit;
a re-encryption unit operable to encrypt the decryption seed value based on the decryption blind value, to generate re-encryption information;
a judging unit operable to judge, based on the encryption information and the re-encryption information, whether the decryption shared key should be outputted;
and
an outputting unit operable, when the judging unit has judged affirmatively, to output the decryption shared key.

11 more elements

A shared-key generation apparatus that notifies a destination apparatus about a shared key in secrecy, the shared-key generation apparatus comprising:

a seed-value generating unit operable to generate a seed value;
a shared-key generating unit operable to generate a blind value and a shared key, from the seed value;
an encryption unit operable to encrypt the seed value based on the blind value, to generate encryption information;
and
a transmitting unit operable to transmit the encryption information.

2 more elements

A shared-key recovery apparatus that receives a shared key from a shared-key generation apparatus in secrecy, the shared-key generation apparatus generating a seed value, generating a blind value and a shared key from the seed value, encrypting the seed value based on the blind value to generate encryption information, and transmitting the encryption information, the shared-key recovery apparatus comprising:

a receiving unit operable to receive the encryption information;
a decryption unit operable to decrypt the encryption information, to generate a decryption seed value;
a shared-key generating unit operable to generate a decryption blind value and a decryption shared key, using the decryption seed value and according to a same shared-key generating method used in the shared-key generation apparatus;
a re-encryption unit operable to encrypt the decryption seed value based on the decryption blind value, to generate re-encryption information;
a judging unit operable to judge, based on the encryption information and the re-encryption information, whether the decryption shared key should be outputted;
and
an outputting unit operable, when the judging unit has judged affirmatively, to output the decryption shared key.

4 more elements

Dependencies are inferred from the claim text.

Key agreement system, shared-key generation apparatus, and shared-key recovery apparatus

Life of this patent

Key agreement system, shared-key generation apparatus, and shared-key recovery apparatus

Life of this patent

Abstract

Claims43