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

• US 20040165726A1
• Filed: 12/02/2003
• Published: 08/26/2004
• Est. Priority Date: 12/03/2002
• Status: Active Grant

• Current Assignee: Piece Future Pte., Ltd.
• Original Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Inventors: Tatebayashi, Makoto, Futa, Yuichi, Ohmori, Motoji, Yamamichi, Masato, Yamamichi, Masami
• Granted Patent: US 7,471,792 B2
• Time in Patent Office: Days
• US Class Current: 380/277
• CPC Class Codes: H04L 2209/04 Masking or blinding
• CPC Class Codes: H04L 2209/60 Digital content management, e.g. content distribution
• CPC Class Codes: H04L 9/085 Secret sharing or secret splitting, e.g. threshold schemes
• CPC Class Codes: H04L 9/0869 involving random numbers or seeds

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 112d, in an encryption apparatus 110d, generates a random number s, and a first function unit 113d generates a functional value G(s) of the random number s, and generates a verification value a and a shared key K from the functional value G(s). An encryption unit 114d generates a first cipher text c1 of the verification value a using a public-key polynomial h, and a second function unit 115d generates a functional value H(a,c1) of the verification value a and the first cipher text c1, and a random-number mask unit 116d generates a second cipher text c2=s xor H(a,c1). A decryption unit 123d, in a decryption apparatus 120d, decrypts the first cipher text c1 using a secret-key polynomial f, to generate a decryption verification value a′. A third function unit 124d generates a functional value H(a′,c1) of the decryption verification value a′ and the first cipher text c1, and a random-number mask removal unit 125d generates a decryption random number s′=c2 xor H(a′,c1). A fourth function unit 126d generates a hash functional value G(s′) of the decryption random number s′, and generates a verification value a″ and a shared key K′ from the functional value G(s′) A comparison unit 127d outputs the shared key K′ if the decryption verification value a′ is equal to the verification value a″.

Claims

1. 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 verification value and a shared key, from the seed value;

a first encryption unit operable to encrypt the verification value to generate first encryption information;

a second encryption unit operable to encrypt the seed value based on the verification value, to generate second encryption information; and

a transmitting unit operable to transmit the first encryption information and the second encryption information, and

the shared-key recovery apparatus includes;

a receiving unit operable to receive the first encryption information and the second encryption information;

a first decryption unit operable to decrypt the first encryption information, to generate a first decryption verification value;

a second decryption unit operable to decrypt the second encryption information based on the first decryption verification value, to generate a decryption seed value;

a second shared-key generating unit operable to generate a second decryption verification value and a decryption shared key, from the decryption seed value and according to a same method as used in the first shared-key generating unit;

a judging unit operable to judge, based on the first decryption verification value and the second decryption verification value, 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.

2. The key agreement system of claim 1, wherein

the shared-key generation apparatus further includes:

an obtaining unit operable to obtain a content; and

an encryption unit operable to encrypt the obtained content using the shared key, to generate an encrypted content,

the transmitting unit further transmits the encrypted content,

the receiving unit further receives the encrypted content, and

the shared-key recovery apparatus further includes;

a decryption unit operable to decrypt the received encrypted content using the decryption shared key, to generate a decrypted content; and

an outputting unit operable to output the decrypted content.

3. 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 verification value and a shared key, from the seed value;

a first encryption unit operable to encrypt the verification value to generate first encryption information;

a second encryption unit operable to encrypt the seed value based on the verification value, to generate second encryption information; and

a transmitting unit operable to transmit the first encryption information and the second encryption information.

4. The shared-key generation apparatus of claim 3, wherein

the seed-value generating unit generates a random number, as the seed value.

5. The shared-key generation apparatus of claim 3, wherein

the shared-key generating unit performs a one-way function on the seed value to generate a functional value, and generates the verification value and the shared key from the functional value.

6. The shared-key generation apparatus of claim 5, wherein

the shared-key generating unit performs, on the seed value, a hash function as the one-way function, to generate the functional value.

7. The shared-key generation apparatus of claim 5, wherein

the shared-key generating unit generates the verification value by setting a part of the functional value as the verification value, and generates the shared key by setting another part of the functional value as the shared key.

8. The shared-key generation apparatus of claim 3, wherein

the shared-key generating unit performs a one-way function on the seed value to generate a functional value, and generates the verification value, the shared key, and a blind value, from the functional value.

9. The shared-key generation apparatus of claim 8, wherein

the first encryption unit includes:

a public-key obtaining subunit operable to obtain a public key; and

a public-key encryption subunit operable to perform a public-key encryption algorithm on the verification value, using the public key and the blind value, to generate the first encryption information.

10. The shared-key generation apparatus of claim 9, wherein

the public-key encryption algorithm conforms to an NTRU cryptosystem,

the public-key obtaining subunit obtains a public-key polynomial generated according to a key-generation algorithm of the NTRU cryptosystem, as the public key, and

the public-key encryption subunit generates a verification-value polynomial from the verification value, generates a blind-value polynomial from the blind value, and encrypts the verification-value polynomial according to an encryption algorithm of the NTRU cryptosystem, using the public-key polynomial as a key, and using the blind-value polynomial to randomize the verification-value polynomial, to generate the first encryption information as a polynomial.

11. The shared-key generation apparatus of claim 3, wherein

the first encryption unit includes:

a public-key obtaining subunit operable to obtain a public key; and

a public-key encryption subunit operable to perform a public-key encryption algorithm on the verification value, using the public key, to generate the first encryption information.

12. The shared-key generation apparatus of claim 11, wherein

the public-key encryption algorithm conforms to an NTRU cryptosystem,

the public-key obtaining subunit obtains a public-key polynomial generated according to a key-generation algorithm of the NTRU cryptosystem, as the public key, and

the public-key encryption subunit generates a verification-value polynomial from the verification value, generates a blind value, generates a blind-value polynomial from the blind value, and encrypts the verification-value polynomial according to an encryption algorithm of the NTRU cryptosystem, using the public-key polynomial as a key, and using the blind-value polynomial to randomize the verification-value polynomial, to generate the first encryption information as a polynomial.

13. The shared-key generation apparatus of claim 3, wherein

the second encryption unit performs a one-way function on the verification value to generate a functional value, and performs an encryption algorithm, on the seed value, using the functional value, to generate the second encryption information.

14. The shared-key generation apparatus of claim 13, wherein

the second encryption unit performs bitwise exclusive-or as the encryption algorithm, on the functional value and the seed value, to generate the second encryption information.

15. The shared-key generation apparatus of claim 13, wherein

the second encryption unit performs a symmetric key encryption algorithm as the encryption algorithm, on the functional value and the seed value, to generate the second encryption information.

16. The shared-key generation apparatus of claim 13, wherein

the second encryption unit performs addition as the encryption algorithm, on the functional value and the seed value, to generate the second encryption information.

17. The shared-key generation apparatus of claim 13, wherein

the second encryption unit performs multiplication as the encryption algorithm, on the functional value and the seed value, to generate the second encryption information.

18. The shared-key generation apparatus of claim 13, wherein

the second encryption unit performs, on the verification value, a hash function as the one-way function, to generate the functional value.

19. The shared-key generation apparatus of claim 3, wherein

the second encryption unit performs an encryption algorithm on the seed value using the verification value, to generate the second encryption information.

20. The shared-key generation apparatus of claim 3, wherein

the second encryption unit encrypts the seed value using the verification value and the first encryption information.

21. The shared-key generation apparatus of claim 20, wherein

the second encryption unit performs a one-way function on the verification value and the first encryption information, to generate the functional value, and performs an encryption algorithm on the seed value using the functional value, to generate the second encryption information.

22. The shared-key generation apparatus of claim 21, wherein

the second encryption unit performs bitwise exclusive-or as the encryption algorithm, on the functional value and the seed value, to generate the second encryption information.

23. The shared-key generation apparatus of claim 3, further comprising:

an obtaining unit operable to obtain a content; and

an encryption unit operable to encrypt the obtained content using the shared key, to generate an encrypted content, wherein

the transmitting unit further transmits the encrypted content.

24. 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 verification value and a shared key from the seed value, encrypting the verification value to generate first encryption information, encrypting the seed value based on the verification value to generate second encryption information, and transmitting the first encryption information and the second encryption information, the shared-key recovery apparatus comprising:

a receiving unit operable to receive the first encryption information and the second encryption information;

a first decryption unit operable to decrypt the first encryption information, to generate a first decryption verification value;

a second decryption unit operable to decrypt the second encryption information based on the first decryption verification value, to generate a decryption seed value;

a shared-key generating unit operable to generate a second decryption verification value and a decryption shared key, from the decryption seed value and according to a same method as used in the shared-key generation apparatus;

a judging unit operable to judge, based on the first decryption verification value and the second decryption verification value, 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.

25. The shared-key recovery apparatus of claim 24, wherein

the shared-key generation apparatus obtains a public key, and performs a public-key encryption algorithm on the verification value, using the public key, to generate the first encryption information, and

the first decryption unit includes:

a secret-key obtaining subunit operable to obtain a secret key that corresponds to the public key; and

a public-key decryption subunit operable to perform a public-key decryption algorithm on the first encryption information, to generate the first decryption verification value, the public-key decryption algorithm corresponding to the public-key encryption algorithm.

26. The shared-key recovery apparatus of claim 25, wherein

the public-key encryption algorithm and the public-key decryption algorithm confirm to an NTRU cryptosystem,

the shared-key generation apparatus obtains, as the public key, a public-key polynomial generated according to a key-generation algorithm of the NTRU cryptosystem, generates a verification-value polynomial from the verification value, generates a blind value, generates a blind-value polynomial from the blind value, and encrypts the verification-value polynomial according to an encryption algorithm of the NTRU cryptosystem, using the public-key polynomial as a key, and using the blind-value polynomial to randomize the verification-value polynomial, to generate the first encryption information as a polynomial,

the receiving unit receives the first encryption information as a polynomial,

the secret-key obtaining subunit obtains, as the secret key, a secret-key polynomial generated according to the key-generation algorithm of the NTRU cryptosystem, and

the public-key decryption subunit decrypts the first encryption information as a polynomial, according to a decryption algorithm corresponding to the NTRU cryptosystem'"'"'s encryption algorithm, using the secret-key polynomial as a key, to generate a decryption verification-value polynomial, and generates the first decryption verification value from the decryption verification-value polynomial.

27. The shared-key recovery apparatus of claim 24, wherein

the shared-key generation apparatus performs a one-way function on the verification value, to generate a functional value, and performs an encryption algorithm on the seed value using the functional value, to generate the second encryption information, and

the second decryption unit performs the one-way function on the first decryption verification value, to generate a decryption functional value, and performs, on the second encryption information, a decryption algorithm corresponding to the encryption algorithm, using the decryption functional value, to generate the decryption seed value.

28. The shared-key recovery apparatus of claim 27, wherein

the shared-key generation apparatus performs, on the functional value and the seed value, bitwise exclusive-or as the encryption algorithm, to generate the second encryption information, and

the second decryption unit performs, on the decryption functional value and the second encryption information, bitwise exclusive-or as the decryption algorithm, to generate the decryption seed value.

29. The shared-key recovery apparatus of claim 27, wherein

the shared-key generation apparatus performs, on the functional value and the seed value, a symmetric key encryption algorithm as the encryption algorithm, to generate the second encryption information, and

the second decryption unit performs, on the decryption functional value and the second encryption information, a symmetric key decryption algorithm as the decryption algorithm, to generate the decryption seed value, the symmetric key decryption algorithm corresponding to the symmetric key encryption algorithm.

30. The shared-key recovery apparatus of claim 27, wherein

the shared-key generation apparatus performs, on the functional value and the seed value, addition as the encryption algorithm, to generate the second encryption information, and

the second decryption unit performs, on the decryption functional value and the second encryption information, subtraction as the decryption algorithm, to generate the decryption seed value.

31. The shared-key recovery apparatus of claim 27, wherein

the shared-key generation apparatus performs, on the functional value and the seed value, multiplication as the encryption algorithm, to generate the second encryption information, and

the second decryption unit performs, on the decryption functional value and the second encryption information, division as the decryption algorithm, to generate the decryption seed value.

32. The shared-key recovery apparatus of claim 27, wherein

the shared-key generation apparatus performs, on the verification value, a hash function as the one-way function, to generate the functional value, and

the second decryption unit performs, on the first decryption verification value, the hash function as the one-way function, to generate the decryption functional value.

33. The shared-key recovery apparatus of claim 24, wherein

the shared-key generation apparatus performs an encryption algorithm on the seed value using the verification value, to generate the second encryption information, and

the second decryption unit performs a decryption algorithm corresponding to the encryption algorithm, on the second encryption information using the first decryption verification value, to generate the decryption seed value.

34. The shared-key recovery apparatus of claim 24, wherein

the shared-key generation apparatus encrypts the seed value using the verification value and the first encryption information, and

the second decryption unit decrypts the second encryption information, using the first decryption verification value and the first encryption information, to generate the decryption seed value.

35. The shared-key recovery apparatus of claim 34, wherein

the shared-key generation apparatus performs a one-way function on the verification value and the first encryption information, to generate a functional value, and performs an encryption algorithm on the seed value using the functional value, to generate the second encryption information, and

the second decryption unit performs the one-way function on the first decryption verification value and the first encryption information, to generate a decryption functional value, and performs a decryption algorithm corresponding to the encryption algorithm, on the second encryption information, using the decryption functional value, to generate the decryption seed value.

36. The shared-key recovery apparatus of claim 35, wherein

the shared-key generation apparatus performs bitwise exclusive-or as the encryption algorithm, on the functional value and the seed value, to generate the second encryption information, and

the second decryption unit performs bitwise exclusive-or as the decryption algorithm, on the decryption functional value and the second encryption information, to generate the decryption seed value.

37. The shared-key recovery apparatus of claim 24, wherein

the shared-key generation apparatus performs a one-way function on the seed value, to generate a functional value, and generates the verification value and the shared key from the functional value, and

the shared-key generating unit performs the one-way function on the decryption seed value, to generate a decryption functional value, and generates the second decryption verification value and the decryption shared key from the decryption functional value.

38. The shared-key recovery apparatus of claim 37, wherein

the shared-key generation apparatus performs, on the seed value, a hash function as the one-way function, to generate the functional value, and

the shared-key generating unit performs, on the decryption seed value, the hash function as the one-way function, to generate the decryption functional value.

39. The shared-key recovery apparatus of claim 37, wherein

the shared-key generation apparatus generates the verification value by setting a part of the functional value as the verification value, and generates the shared key by setting another part of the functional value as the shared key, and

the shared-key generating unit generates the second decryption verification value by setting a part of the decryption functional value as the second decryption verification value, and generates the decryption shared key by setting another part of the decryption functional value as the decryption shared key.

40. The shared-key recovery apparatus of claim 24, wherein

the shared-key generation apparatus performs a one-way function on the seed value, to generate a functional value, generates the verification value, the shared key, and a blind value, from the functional value, obtains a public key, and performs a public-key encryption algorithm on the verification value, using the public key and the blind value, to generate the first encryption information, and

the shared-key generating unit performs the one-way function on the decryption seed value, to generate a decryption functional value, and generates, from the decryption functional value, the second decryption verification value, the decryption shared key, and the decryption blind value.

41. The shared-key recovery apparatus of claim 40, wherein

the shared-key generation apparatus obtains a public key, performs a public-key encryption algorithm on the verification value, using the public key and the blind value, to generate the first encryption information, and

the judging unit, instead of performing the judging based on the first decryption verification value and the second decryption verification value, includes:

a public-key obtaining subunit operable to obtain the public key;

a re-encryption subunit operable to perform the public-key encryption algorithm on one of the first decryption verification value and the second decryption verification value, using the public key and the decryption blind value, to generate re-encryption information; and

a judging subunit operable to judge, based on the first encryption information and the re-encryption information, whether the decryption shared key should be outputted or not.

42. The shared-key recovery apparatus of claim 41, wherein

the judging subunit compares the first encryption information and the re-encryption information, thereby judging that the decryption shared key should be outputted if the first encryption information is identical to the re-encryption information.

43. The shared-key recovery apparatus of claim 41, wherein

the public-key encryption algorithm conforms to an NTRU cryptosystem,

the shared-key generation apparatus obtains, as the public key, a public-key polynomial generated according to a key-generation algorithm of the NTRU cryptosystem, generates a verification-value polynomial from the verification value, generates a blind-value polynomial from the blind value, and encrypts the verification-value polynomial according to an encryption algorithm of the NTRU cryptosystem, using the public-key polynomial as a key, and using the blind-value polynomial to randomize the verification-value polynomial, to generate the first encryption information as a polynomial,

the public-key obtaining subunit obtains the public-key polynomial, and

the re-encryption subunit generates a decryption verification-value polynomial from the second decryption verification value, generates a decryption blind-value polynomial from the decryption blind value, and encrypts the decryption verification-value polynomial according to the encryption algorithm of the NTRU cryptosystem, using the public-key polynomial as a key, and using the decryption blind-value polynomial to randomize the decryption verification-value polynomial, to generate the re-encryption information as a polynomial.

44. The shared-key recovery apparatus of claim 24, wherein

the judging unit compares the first decryption verification value and the second decryption verification value, thereby judging that the decryption shared key should be outputted if the first decryption verification value is identical to the second decryption verification value.

45. The shared-key recovery apparatus of claim 24, wherein

the shared-key generation apparatus further obtains a content, encrypts the content using the shared key to generate an encrypted content, and transmits the encrypted content,

the receiving unit further receives the encrypted content, and

the shared-key recovery apparatus further comprises:

a decryption unit operable to decrypt the received encrypted content using the decryption shared key, to generate a decrypted content; and

an outputting unit operable to output the decrypted content.

46. A shared-key generating method used in a shared-key generation apparatus that notifies a destination apparatus about a shared key, in secrecy, the shared-key generating method comprising:

a seed-value generating step of generating a seed value;

a shared-key generating step of generating a verification value and a shared key, from the seed value;

a first encryption step of encrypting the verification value to generate first encryption information;

a second encryption step of encrypting the seed value based on the verification value, to generate second encryption information; and

a transmitting step of transmitting the first encryption information and the second encryption information.

47. A shared-key generating program used in a shared-key generation apparatus that notifies a destination apparatus about a shared key, in secrecy, the shared-key generating program comprising:

a seed-value generating step of generating a seed value;

a shared-key generating step of generating a verification value and a shared key, from the seed value;

a first encryption step of encrypting the verification value to generate first encryption information;

a second encryption step of encrypting the seed value based on the verification value, to generate second encryption information; and

a transmitting step of transmitting the first encryption information and the second encryption information.

48. The shared-key generating program of claim 47, wherein

the shared-key generating program is recorded in a computer-readable recording medium.

49. A shared-key recovery method used in 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 verification value and a shared key from the seed value, encrypting the verification value to generate first encryption information, encrypting the seed value based on the verification value to generate second encryption information, and transmitting the first encryption information and the second encryption information, the shared-key recovery method comprising:

a receiving-step of receiving the first encryption information and the second encryption information;

a first decryption step of decrypting the first encryption information, to generate a first decryption verification value;

a second decryption step of decrypting the second encryption information based on the first decryption verification value, to generate a decryption seed value;

a shared-key generating step of generating a second decryption verification value and a decryption shared key, from the decryption seed value and according to a same method as used in the shared-key generation apparatus;

a judging step of judging, based on the first decryption verification value and the second decryption verification value, whether the decryption shared key should be outputted; and

an outputting step, when the judging unit has judged affirmatively, of outputting the decryption shared key.

50. A shared-key recovery program used in 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 verification value and a shared key from the seed value, encrypting the verification value to generate first encryption information, encrypting the seed value based on the verification value to generate second encryption information, and transmitting the first encryption information and the second encryption information, the shared-key recovery program comprising:

a receiving step of receiving the first encryption information and the second encryption information;

a first decryption step of decrypting the first encryption information, to generate a first decryption verification value;

a second decryption step of decrypting the second encryption information based on the first decryption verification value, to generate a decryption seed value;

a shared-key generating step of generating a second decryption verification value and a decryption shared key, from the decryption seed value and according to a same method as used in the shared-key generation apparatus;

a judging step of judging, based on the first decryption verification value and the second decryption verification value, whether the decryption shared key should be outputted; and

an outputting step, when the judging unit has judged affirmatively, of outputting the decryption shared key.

51. The shared-key recovery program of claim 50, wherein

the shared-key recovery program is recorded in a computer-readable recording medium.