Outsourcing the Decryption of Functional Encryption Ciphertexts

• US 20120300936A1
• Filed: 05/22/2012
• Published: 11/29/2012
• Est. Priority Date: 05/24/2011
• Status: Active Grant

• Current Assignee: NTT Research, Inc. (Nippon Telegraph and Telephone Corporation)
• Original Assignee: Zeutro LLC
• Inventors: Green, Matthew Daniel
• Granted Patent: US 9,049,023 B2
• Time in Patent Office: Days
• US Class Current: 380/278
• CPC Class Codes: H04L 2209/76 Proxy, i.e. using intermediary entity to perform cryptographic operations network architectures or network communication protocols using hop-by-hop encryption H04L63/0464
• CPC Class Codes: H04L 9/088 Usage controlling of secret information, e.g. techniques for restricting cryptographic keys to pre-authorized uses, different access levels, validity of crypto-period, different key- or password length, or different strong and weak cryptographic algorithms network architectures or network communication protocols for using time-dependent keys in a packet data network H04L63/068
• CPC Class Codes: H04L 9/3073 involving pairings, e.g. identity based encryption [IBE], bilinear mappings or bilinear pairings, e.g. Weil or Tate pairing

Abstract

Functional encryption (FE) ciphertext is transformed into partially-decrypted (PD) ciphertext. The PD ciphertext has a shorter bit length than the FE ciphertext, or the decryption time of the PD ciphertext is less than the decryption time of the FE ciphertext. The FE ciphertext can be an attribute-based encryption ciphertext. The transformation can be performed with a transformation key generated by an authority with a master key or by a user with a decryption key. The transformation can also be performed, without a transformation key, based on unencrypted components of the FE ciphertext and on auxiliary information associated with the unencrypted components of the FE ciphertext. The PD ciphertext can require less transmission time across a network than the FE ciphertext. The PD ciphertext can require less time to decrypt than the FE ciphertext, particularly when the computational resources performing the decryption are limited.

Claims

1. A method for processing a functional encryption ciphertext, the method comprising the steps of:

receiving the functional encryption ciphertext;

transforming the functional encryption ciphertext into a partially-decrypted ciphertext; and

sending the partially-decrypted ciphertext.

2. The method of claim 1, wherein the functional encryption ciphertext is an attribute-based encryption ciphertext.

3. The method of claim 1, further comprising the step of:

receiving a transformation key;

wherein the step of transforming the functional encryption ciphertext is based at least in part on the transformation key.

4. The method of claim 3, wherein the transformation key is generated based at least in part on a master key of an authority.

5. The method of claim 3, wherein the transformation key is generated based at least in part on a decryption key of a user.

6. The method of claim 1, wherein the functional encryption ciphertext comprises encrypted elements and unencrypted elements, further comprising the step of:

receiving auxiliary information;

wherein the step of transforming the functional encryption ciphertext is based at least in part on the unencrypted elements and the auxiliary information.

7. The method of claim 1, wherein:

the step of receiving the functional encryption ciphertext comprises the step of receiving the functional encryption ciphertext at a proxy; and

the step of sending the partially-decrypted ciphertext comprises the step of sending the partially-decrypted ciphertext to a user equipment of a user.

8. The method of claim 1, wherein:

the step of receiving the functional encryption ciphertext comprises the step of receiving the functional encryption ciphertext at a first proxy; and

the step of sending the partially-decrypted ciphertext comprises the step of sending the partially-decrypted ciphertext to a second proxy.

9. The method of claim 1, wherein:

the step of receiving the functional encryption ciphertext comprises the step of receiving the functional encryption ciphertext at a first computational system; and

the step of sending the partially-decrypted ciphertext comprises the step of sending the partially-decrypted ciphertext to a second computational system, wherein the second computational system is communicatively coupled to the first computational system by a local communications interface.

10. The method of claim 9, wherein at least one of the first computational system and the second computational system is a smartcard.

11. A method for processing a functional encryption ciphertext, the method comprising the steps of:

receiving a first partially-decrypted ciphertext, wherein the first partially-decrypted ciphertext was generated by transformation of the functional encryption ciphertext;

transforming the first partially-decrypted ciphertext into a second partially-decrypted ciphertext; and

sending the second partially-decrypted ciphertext.

12. The method of claim 11, wherein the functional encryption ciphertext is an attribute-based encryption ciphertext.

13. The method of claim 11, further comprising the step of:

receiving a transformation key;

wherein the step of transforming the functional encryption ciphertext is based at least in part on the transformation key.

14. The method of claim 13, wherein the transformation key is generated based at least in part on a master key of an authority.

15. The method of claim 13, wherein the transformation key is generated based at least in part on a decryption key of a user.

16. The method of claim 11, wherein the first-partially decrypted ciphertext comprises encrypted elements and unencrypted elements, further comprising the step of:

receiving auxiliary information;

wherein the step of transforming the first-partially decrypted ciphertext is based at least in part on the unencrypted elements and the auxiliary information.

17. The method of claim 11, wherein:

the step of receiving a first partially-decrypted ciphertext comprises the step of receiving the first partially-decrypted ciphertext at a proxy; and

the step of sending the second partially-decrypted ciphertext comprises the step of sending the second partially-decrypted ciphertext to a user equipment.

18. The method of claim 11, wherein:

the step of receiving a first partially-decrypted ciphertext comprises the step of receiving the first partially-decrypted ciphertext at a first proxy; and

the step of sending the second partially-decrypted ciphertext comprises the step of sending the partially-decrypted ciphertext to a second proxy.

19. A method for decrypting a functional encryption ciphertext, the method comprising the steps of:

receiving a partially-decrypted ciphertext, wherein the partially-decrypted ciphertext was transformed from the functional encryption ciphertext;

receiving a decryption key of a user; and

decrypting, based at least in part on the decryption key of the user, the partially-decrypted ciphertext into plaintext.

20. The method of claim 19, wherein the functional encryption ciphertext is an attribute-based encryption ciphertext.

21. The method of claim 19, further comprising the step of checking the integrity of:

the partially-decrypted ciphertext;

or

the plaintext.

22. The method of claim 19, wherein:

the step of receiving a partially-decrypted ciphertext comprises the step of receiving the partially-decrypted ciphertext at a user equipment of the user; and

the step of decrypting is performed by the user equipment.

23. The method of claim 19, wherein the partially-decrypted ciphertext was transformed from the functional encryption ciphertext by a first computational system, wherein:

the step of receiving the partially-decrypted ciphertext comprises the step of receiving the partially-decrypted ciphertext at a second computational system, wherein the second computational system is communicatively coupled to the first computational system by a local communications interface; and

the step of decrypting is performed by the second computational system.

24. The method of claim 23, wherein at least one of the first computational system and the second computational system is a smartcard.

25. A method for decrypting a functional encryption ciphertext, the method comprising the steps of:

receiving the functional encryption ciphertext at a computational system;

transforming, in a first process operating in the computational system, the functional encryption ciphertext into a partially-decrypted ciphertext; and

decrypting, in a second process operating in the computational system, wherein the second process is isolated from the first process, the partially-decrypted ciphertext into plaintext.

26. The method of claim 25, wherein the functional encryption ciphertext is an attribute-based encryption ciphertext.

27. The method of claim 25, wherein the step of transforming is based at least in part on a transformation key.

28. The method of claim 27, wherein the transformation key is generated based at least in part on a master key of an authority.

29. The method of claim 27, wherein the transformation key is generated based at least in part on a decryption key of a user.

30. The method of claim 25, wherein the step of decrypting is based at least in part on a decryption key of a user, wherein the decryption key of the user is accessible to the second process, and wherein the decryption key of the user is not accessible to the first process.

31. The method of claim 25, further comprising the step of checking the integrity of:

the partially-decrypted ciphertext;

or

the integrity of the plaintext.

32. The method of claim 25, wherein the first process and the second process are supervised by a kernel of an operating system in the computational system.

33. A method for decrypting a functional encryption ciphertext, the method comprising the steps of:

receiving the functional encryption ciphertext at a computational system;

transforming, in a first virtual machine operating in the computational system, the functional encryption ciphertext into a partially-decrypted ciphertext; and

decrypting, in a second virtual machine operating in the computational system, the partially-decrypted ciphertext into plaintext.

34. The method of claim 33, wherein the functional encryption ciphertext is an attribute-based encryption ciphertext.

35. The method of claim 33, wherein the step of transforming is based at least in part on a transformation key.

36. The method of claim 35, wherein the transformation key is generated based at least in part on a master key of an authority.

37. The method of claim 35, wherein the transformation key is generated based at least in part on a decryption key of a user.

38. The method of claim 33, wherein the step of decrypting is based at least in part on a decryption key of a user, wherein the decryption key of the user is accessible to the second virtual machine, and wherein the decryption key of the user is not accessible to the first virtual machine.

39. The method of claim 33, further comprising the step of checking the integrity of:

the partially-decrypted ciphertext;

or

the plaintext.

40. A method for decrypting a functional encryption ciphertext, the method comprising the steps of:

receiving the functional encryption ciphertext;

receiving a decryption key of a user;

transforming the functional encryption ciphertext into a partially-decrypted ciphertext; and

decrypting, based at least in part on the decryption key of the user, the partially-decrypted ciphertext into plaintext.

41. The method of claim 40, wherein the functional encryption ciphertext is an attribute-based encryption ciphertext.

42. The method of claim 40, wherein the step of transforming the functional encryption ciphertext into a partially-decrypted ciphertext comprises the steps of:

generating a transformation key based at least in part on the decryption key of the user; and

transforming, based at least in part on the transformation key, the functional encryption ciphertext into the partially-decrypted ciphertext.

43. The method of claim 40, further comprising the step of:

checking the integrity of the plaintext.

44. A method for decrypting a functional encryption ciphertext, the method comprising the steps of:

receiving, at a user equipment of a user, the functional ciphertext;

receiving, at the user equipment of the user, a decryption key of the user;

sending the functional ciphertext from the user equipment of the user to a proxy;

receiving, at the proxy, a transformation key;

transforming, at the proxy, based at least in part on the transformation key, the functional ciphertext into a partially-decrypted ciphertext;

sending the partially-decrypted ciphertext from the proxy to the user equipment of the user; and

decrypting, at the user equipment of the user, based at least in part on the decryption key of the user, the partially-decrypted ciphertext into plaintext.

45. The method of claim 44, wherein the functional encryption ciphertext is an attribute-based encryption ciphertext.

46. The method of claim 44, wherein the transformation key is generated based at least in part on:

a master key of an authority;

or

the decryption key of the user.

47. The method of claim 44, further comprising the step of checking the integrity of:

the partially-decrypted ciphertext;

or

the plaintext.

48. A computer readable medium storing computer program instructions, which, when executed by a processor, cause the processor to perform a method for processing a functional encryption ciphertext, the method comprising the steps of:

receiving the functional encryption ciphertext;

transforming the functional encryption ciphertext into a partially-decrypted ciphertext; and

sending the partially-decrypted ciphertext.

49. The computer readable medium of claim 48, wherein the functional encryption ciphertext is an attribute-based encryption ciphertext.

50. The computer readable medium of claim 48, wherein the method further comprises the step of:

receiving a transformation key;

wherein the step of transforming the functional encryption ciphertext is based at least in part on the transformation key.

51. The computer readable medium of claim 48, wherein the functional encryption ciphertext comprises encrypted elements and unencrypted elements, wherein the method further comprises the step of:

receiving auxiliary information;

wherein the step of transforming the functional encryption ciphertext is based at least in part on the unencrypted elements and the auxiliary information.

52. A computer readable medium storing computer program instructions, which, when executed by a processor, cause the processor to perform a method for decrypting a functional encryption ciphertext, the method comprising the steps of:

receiving a partially-decrypted ciphertext, wherein the partially-decrypted ciphertext was transformed from the functional encryption ciphertext;

receiving a decryption key of a user; and

decrypting, based at least in part on the decryption key of the user, the partially-decrypted ciphertext into plaintext.

53. The computer readable medium of claim 52, wherein the functional encryption ciphertext is an attribute-based encryption ciphertext.

54. A computational system comprising:

a processor;

memory operatively coupled to the processor; and

a data storage device operatively coupled to the processor;

wherein the data storage device stores computer program instructions, which, when executed by the processor, cause the processor to perform a method for transforming a functional encryption ciphertext, the method comprising the steps of;

receiving the functional encryption ciphertext;

transforming the functional encryption ciphertext into a partially-decrypted ciphertext; and

sending the partially-decrypted ciphertext.

55. The computational system of claim 54, wherein the computational system comprises a smartcard.

56. The computational system of claim 54, wherein the functional encryption ciphertext is an attribute-based encryption ciphertext.

57. The computational system of claim 54, wherein the method further comprises the step of:

receiving a transformation key;

wherein the step of transforming the functional encryption ciphertext is based at least in part on the transformation key.

58. The computational system of claim 54, wherein the functional encryption ciphertext comprises encrypted elements and unencrypted elements, wherein the method further comprises the step of:

receiving auxiliary information;

wherein the step of transforming the functional encryption ciphertext is based at least in part on the unencrypted elements and the auxiliary information.

59. A computational system comprising:

a processor;

memory operatively coupled to the processor; and

a data storage device operatively coupled to the processor;

wherein the data storage device stores computer program instructions, which, when executed by the processor, cause the processor to perform a method for processing a functional encryption ciphertext, the method comprising the steps of;

receiving a first-partially decrypted ciphertext, wherein the first partially-decrypted ciphertext was generated by transformation of the functional encryption ciphertext;

transforming the first partially-decrypted ciphertext into a second partially-decrypted ciphertext; and

sending the second partially-decrypted ciphertext.

60. The computational system of claim 59, wherein the functional encryption ciphertext is an attribute-based encryption ciphertext.

61. The computational system of claim 59, wherein the method further comprises the step of:

receiving a transformation key;

wherein the step of transforming the functional encryption ciphertext is based at least in part on the transformation key.

62. The computational system of claim 59, wherein the functional encryption ciphertext comprises encrypted elements and unencrypted elements, wherein the method further comprises the step of:

receiving auxiliary information;

wherein the step of transforming the functional encryption ciphertext is based at least in part on the unencrypted elements and the auxiliary information.

63. A computational system comprising:

a processor;

memory operatively coupled to the processor; and

a data storage device operatively coupled to the processor;

wherein the data storage device stores computer program instructions, which, when executed by the processor, cause the processor to perform a method for decrypting a functional encryption ciphertext, the method comprising the steps of;

receiving a partially-decrypted ciphertext, wherein the partially-decrypted ciphertext was transformed from the functional encryption ciphertext;

receiving a decryption key of a user; and

decrypting, based at least in part on the decryption key of the user, the partially-decrypted ciphertext into plaintext.

64. The computational system of claim 63, wherein the computational system comprises a smartcard.

65. The computational system of claim 63, wherein the functional encryption ciphertext is an attribute-based encryption ciphertext.

66. A computational system comprising:

a processor;

memory operatively coupled to the processor; and

a data storage device operatively coupled to the processor;

wherein the data storage device stores computer program instructions, which, when executed by the processor, cause the processor to perform a method for processing a functional encryption ciphertext, the method comprising the steps of;

receiving, in a first process, the functional encryption ciphertext;

transforming, in the first process, the functional encryption ciphertext into a partially-decrypted ciphertext; and

decrypting, in a second process, wherein the second process is isolated from the first process, the partially-decrypted ciphertext into plaintext.

67. The computational system of claim 66, wherein the functional encryption ciphertext is an attribute-based encryption ciphertext.

68. The computational system of claim 66, wherein the step of transforming is based at least in part on a transformation key.

69. The computational system of claim 66, wherein the step of decrypting is based at least in part on a decryption key of a user, wherein the decryption key of the user is accessible to the second process, and wherein the decryption key of the user is not accessible to the first process.

70. A computational system comprising:

a processor;

memory operatively coupled to the processor; and

a data storage device operatively coupled to the processor;

wherein the data storage device stores computer program instructions, which, when executed by the processor, cause the processor to perform a method for transforming a functional encryption ciphertext, the method comprising the steps of;

receiving, in a first virtual machine, the functional encryption ciphertext;

transforming, in the first process, the functional encryption ciphertext into a partially-decrypted ciphertext; and

decrypting, in a second virtual machine, the partially-decrypted ciphertext into plaintext.

71. The computational system of claim 70, wherein the functional encryption ciphertext is an attribute-based encryption ciphertext.

72. The computational system of claim 70, wherein the step of transforming is based at least in part on a transformation key.

73. The computational system of claim 70, wherein the step of decrypting is based at least in part on a decryption key of a user, wherein the decryption key of the user is accessible to the second virtual machine, and wherein the decryption key of the user is not accessible to the first virtual machine.

74. A computational system comprising:

a processor;

memory operatively coupled to the processor; and

a data storage device operatively coupled to the processor;

wherein the data storage device stores computer program instructions, which, when executed by the processor, cause the processor to perform a method for decrypting a functional encryption ciphertext, the method comprising the steps of;

receiving the functional encryption ciphertext;

receiving a decryption key of a user;

transforming the functional encryption ciphertext into a partially-decrypted ciphertext; and

decrypting, based at least in part on the decryption key of the user, the partially-decrypted ciphertext into plaintext.

75. The computational system of claim 74, wherein the functional encryption ciphertext is an attribute-based encryption ciphertext.

76. The computational system of claim 74, wherein the step of transforming the functional encryption ciphertext into a partially-decrypted ciphertext comprises the steps of:

generating a transformation key based at least in part on the decryption key of the user; and

transforming, based at least in part on the transformation key, the functional encryption ciphertext into the partially-decrypted ciphertext.