METHOD AND APPARATUS FOR TIME-LAPSE CRYPTOGRAPHY

• US 20100185863A1
• Filed: 11/30/2007
• Published: 07/22/2010
• Est. Priority Date: 12/01/2006
• Status: Active Grant

• Current Assignee: President and Fellows of Harvard College (Harvard Corporation)
• Original Assignee: President and Fellows of Harvard College (Harvard Corporation)
• Inventors: Thorpe, Christopher A., Rabin, Michael O.
• Granted Patent: US 8,526,621 B2
• Time in Patent Office: Days
• US Class Current: 713/171
• CPC Class Codes: H04L 2209/42 Anonymization, e.g. involving pseudonyms
• CPC Class Codes: H04L 2209/463 Electronic voting
• CPC Class Codes: H04L 9/085 Secret sharing or secret splitting, e.g. threshold schemes

Abstract

According to one aspect, provided is a construction and specification for an implementation of a new cryptographic primitive, “Time-Lapse Cryptography”, with which a sender can encrypt a message so that it is guaranteed to be revealed at an exact moment in the future, even if this revelation turns out to be undesirable to the sender. In one embodiment, a Time-Lapse Cryptography Service is provided (“the Service”) based on a network of parties. Senders encrypt their messages with this public key whose secret key is not known to anyone—not even a trusted third party—until a predefined and specific future time T+δ, at which point the secret key is constructed and published. In one example, the secret key can only be known after it is constructed. At or after that time, anyone can decrypt the cipher text using this secret key. Other embodiments describe other applications of such a service, for example, one embodiment is used in sealed bid auctions, others in insider stock sales, clinical trials, and electronic voting, among a variety of possible implementations. In one embodiment, a method for cryptographic encoding is provided, including generation of cryptographic key components by a plurality of parties, where participation of the parties is verified. A public key is constructed from a plurality of key components,

Claims

1. A computer implemented method for cryptographic key creation, the method comprising the acts of:

accepting a cryptographic key component generated on a computer system by a plurality of parties thereby yielding a plurality of cryptographic key components;

verifying participation of the plurality of parties;

constructing, by a computer processor, a public key based on at least a portion of the plurality of cryptographic key components; and

generating, after a predetermined time, a secret key based on at least a portion of the plurality of cryptographic key components.

2. The method according to claim 1, wherein the act of generating a cryptographic key component further comprises an act of generating a public key component.

3. The method according to claim 2, further comprising an act of publishing the public key component wherein the published key component is accompanied by a digital signature.

5. The method according to claim 3, wherein publishing the public key component comprises posting the public key component and signature to a bulletin board.

6. The method according to claim 3, wherein the act of verifying participation of the plurality of parties further comprises an act of disqualifying any of the plurality of parties that did not publish the public key component.

7. The method according to claim 1, wherein the act of generating a cryptographic key component further comprises an act of generating a secret key component.

8. The method according to claim 7, further comprising an act of transforming the secret key component.

9. The method according to claim 8, wherein the secret key component is transformed into at least one value.

10. The method according to claim 8, wherein the act of transforming the secret key component further comprises calculating and communicating a secret share of the secret key component.

11. The method according to claim 8, further comprising an act of communicating the transformed secret key component to at least one of the plurality of parties wherein the act of communicating the transformed secret key component occurs through secret sharing.

13. The method according to claim 11, further comprising an act of digitally signing the transformed secret key component.

14. The method according to claim 8, further comprising an act of generating a commitment for each of the transformed secret key components.

15. The method according to claim 14, further comprising an act of communicating the commitment and a digital signature of the commitment.

16. The method according to claim 15, wherein the act of communicating further comprises an act of posting the commitment and the signature to a bulletin board.

18. The method according to claim 11, further comprising an act of disqualifying any of the plurality of parties that communicates an invalid transformed secret key component.

20. The method according to claim 1, further comprising an act of publishing the public key by at least a portion of the plurality of parties.

21. The method according to claim 20, further comprising an act of verifying the public key.

22. The method according to claim 21, wherein the act of verifying a public key includes verifying a correspondence between the published cryptographic key and the transformed secret key components.

23. The method according to claim 1, further comprising the acts of:

establishing the predetermined time; and

further comprising an act of publishing a secret key component during the computation time period.

24. The method according to claim 23, wherein the predetermined time includes a time period for computation.

26. The method according to claim 23, further comprising an act of verifying the secret key component.

27. The method according to claim 26, further comprising an act of reconstructing a secret key component.

28. The method according to claim 23, wherein generating, at a predetermined time, a secret key based, at least in part, on at least a portion of a plurality of cryptographic key components, further comprises constructing the secret key from at least one published secret key component.

30. The method according to claim 28, further comprising an act of publishing the secret key and a signature on the secret key.

4. (canceled)

12. (canceled)

17. The method according to claim 12, further comprising an act of verifying the transformed secret key component.

19. (canceled)

25. (canceled)

29. (canceled)

31. (canceled)

32. (canceled)

33. A computer-readable medium having computer-readable signals stored thereon that define instructions that, as a result of being executed by a computer, instruct the computer to perform a method for cryptographic encoding, the method comprising:

generating a cryptographic key component by a plurality of parties to yield a plurality of cryptographic key components;

verifying participation of the plurality of parties;

constructing a public key based on at least a portion of the plurality of cryptographic key components; and

generating, after a predetermined time, a secret key based on at least a portion of the plurality of cryptographic key components.

34-53. -53. (canceled)

54. A system for cryptographic encoding, the system comprising:

a cryptographic key generation component adapted to create a cryptographic key component for the plurality of parties to yield a plurality of cryptographic key components;

a communication component for communicating between the plurality of parties;

a construction component adapted to construct a public key based on at least a portion of the plurality of cryptographic key components, wherein the construction component is further adapted to generate, after a predetermined time, a secret key, based on at least a portion of a plurality of cryptographic key components; and

a verification component adapted to verify proper participation of the plurality of parties.

55-73. -73. (canceled)