CRYPTOGRAPHIC ENCODING AND DECODING OF SECRET DATA

• US 20100142704A1
• Filed: 10/27/2009
• Published: 06/10/2010
• Est. Priority Date: 10/28/2008
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Heydt-Benjamin, Thomas Scott, Gross, Thomas R., Camenisch, Jan Leonhard
• Granted Patent: US 8,744,077 B2
• Time in Patent Office: Days
• US Class Current: 380/44
• CPC Class Codes: H04L 2209/42 Anonymization, e.g. involving pseudonyms
• CPC Class Codes: H04L 2209/56 Financial cryptography, e.g. electronic payment or e-cash
• CPC Class Codes: H04L 9/0847 involving identity based encryption [IBE] schemes
• CPC Class Codes: H04L 9/3013 involving the discrete logarithm problem, e.g. ElGamal or Diffie-Hellman systems
• CPC Class Codes: H04L 9/3213 using tickets or tokens, e.g. Kerberos network architectures or network communication protocols for entities authentication using tickets in a packet data network H04L63/0807
• CPC Class Codes: H04L 9/3218 using proof of knowledge, e.g. Fiat-Shamir, GQ, Schnorr, ornon-interactive zero-knowledge proofs

Abstract

Methods and apparatus are provided for cryptographically encoding secret data in a data processing system. The secret data is encoded in accordance with a verifiable encryption process to produce a cryptographic construction (θ) having a decryption constraint dependent on the occurrence of a predetermined event. An event-dependent decryption constraint is thereby built into the cryptography, so that there is an intrinsic restriction on the ability to decrypt the encoded secret data which is dependent on occurrence of the predetermined event. Decoding apparatus for such a cryptographic construction is also provided, as well as distributed trust data processing systems providing accountable privacy based on use of such cryptographic constructions.

Claims

1. A method for cryptographically encoding secret data in a data processing system implemented by a computing apparatus, the method comprising:

encoding, by an encoding unit, said secret data in accordance with a verifiable encryption process to produce a cryptographic construction (θ

) having a decryption constraint dependent on the occurrence of a predetermined event, thereby cryptographically encoding secret data in a data processing system.

2. The method according to claim 1, further comprising the steps of:

generating a public key of a public-private keypair which is dependent on an event indicator (t_ω

) indicative of said predetermined event such that extraction of a private key (sk_θ

) of said public-private keypair is dependent on occurrence of said predetermined event indicated by said event indicator (t_ω

); and

encoding said secret data using said public key.

3. The method according to claim 2, further comprising the steps of:

generating said public key of said keypair in accordance with a committed blind anonymous identity-based encryption scheme having an identity string comprising said event indicator (t_ω

).

4. The method according to claim 1, wherein said predetermined event is a time event.

5. The method according to claim 2 wherein said event indicator (t_ω

) comprises a time.

6. The method according to claim 1 wherein said decryption constraint is dependent on the occurrence of a plurality of predetermined events.

7. The method according to claim 1, further comprising transmitting said cryptographic construction (θ

) to a receiving device of said data processing system through a data communications channel.

8. A computer readable article of manufacture tangibly embodying computer readable instructions which, when executed, cause a computer device to implement a method for cryptographically encoding secret data according to claim 1.

9. A distributed trust data processing system for cryptographically encoding and decoding data, comprising:

a user computer, wherein said user computer is adapted to (i) generate a public key of a public-private keypair which is dependent on an event indicator (t_ω

) indicative of a predetermined first event such that extraction of a private key (sk_θ

) of said keypair is also dependent on occurrence of said event indicated by said event indicator (t_ω

), (ii) use said public key to encode secret data in accordance with a verifiable encryption process which produces a cryptographic construction (θ

) having a decryption constraint dependent on the occurrence of said predetermined first event, and (iii) send said cryptographic construction (θ

) to said verifier computer via a data communications network;

a key-extraction computer, wherein said key-extraction computer is adapted to respond to said request from said verifier computer by (i) determining if a predetermined decoding condition, dependent on occurrence of at least one event including said predetermined first event, exists (ii) extracting said private key (sk_θ

) of said keypair and sending said private key (sk_θ

) to said verifier computer if said predetermined decoding condition exists; and

a verifier computer, wherein said verifier computer is adapted to (i) verify that said cryptographic construction (θ

) contains said secret data, (ii) store said cryptographic construction (θ

) in memory (10), (iii) communicate with said key extraction computer via said data communications network to request said private key (sk_θ

) for said cryptographic construction (θ

), and (iv) decode said cryptographic construction on receipt of said private key (sk_θ

);

wherein said user, verifier, and key-extraction computers are adapted for communication via said data communications network.

10. The data processing system according to claim 9, wherein said verifier computer comprises:

a memory unit for storing said cryptographic construction; and

a control logic unit adapted to (i) verify that said cryptographic construction contains secret data, (ii) determine the existence of a predetermined decoding condition which is dependent on the occurrence of at least one event including a predetermined first event, and (iii) decode said cryptographic construction as permitted by a decryption constraint if said at least one event occurred.

11. The data processing system according to claim 10, wherein said secret data is encoded in accordance with a verifiable encryption process such that said cryptographic construction has said decryption constraint which is dependent on the occurrence of said predetermined first event.

12. An apparatus according to claim 10, said apparatus further comprising:

a communications unit for communication via a data communications network with (i) a user computer and (ii) a key-extraction computer of a distributed trust data processing system.

13. An apparatus according to claim 9, wherein said control logic unit further comprises:

a verifier logic unit for verifying that said cryptographic construction (θ

) contains said secret data; and

a key extraction logic unit for extracting a private key (sk_θ

) of a public-private keypair if the predetermined decoding condition exists.

14. An apparatus according to claim 9, wherein said secret data is encoded in said cryptographic construction (θ

) using a public key of said public-private keypair which is dependent on said event indicator (t_ω

) indicative of said predetermined first event such that the extraction of said private key (sk_θ

) of said public-private keypair is dependent on occurrence of said predetermined first event indicated by said event indicator (t_ω

).

15. The apparatus according to claim 9, wherein said predetermined event is a time event.

16. The apparatus according to claim 9, wherein said event indicator (t_ω

) comprises a time.

17. The apparatus according to claim 9, wherein said decryption constraint is dependent on the occurrence of a plurality of predetermined events.

18. The apparatus according to claim 9, further comprising transmitting said cryptographic construction (θ

) to a receiving device of said data processing system through a data communications channel.