Limited-traceability systems

• US 5,712,913 A
• Filed: 02/08/1994
• Issued: 01/27/1998
• Est. Priority Date: 02/08/1994
• Status: Expired due to Term

• Current Assignee: Van Detsan Networks LLC (Intellectual Ventures LLC)
• Original Assignee: Digicash
• Inventors: Chaum, David
• Primary Examiner(s): CANGIALOSI, SALVATORE A
• Application Number:
  US08/193,500
• Time in Patent Office: 1,449 Days
• Field of Search: 320/29, 320/25, 320/30
• US Class Current: 705/74
• CPC Class Codes: G06Q 20/085 involving remote charge determination or related payment systems
• CPC Class Codes: G06Q 20/3678 e-cash details, e.g. blinded, divisible or detecting double spending
• CPC Class Codes: G06Q 20/383 Anonymous user system
• CPC Class Codes: H04L 2209/56 Financial cryptography, e.g. electronic payment or e-cash
• CPC Class Codes: H04L 9/3257 using blind signatures

Abstract

Cryptographic methods and apparatus for payment and related transaction systems are disclosed that allow some kinds of tracing under some conditions and make substantially infeasible other kinds of tracing under other conditions. Examples include: allowing tracing if and only if agreed sets of trustees cooperate; tracing from a payment to the payer by cooperation of a set of trustees; tracing from a payment to the payer without revealing to trustees which payer is being traced or which payment; identifying all payments by a payer provided appropriate trustees cooperate; and identifying all payments by a payer under investigation without trustees learning which payer and/or which payments;

Other examples include: limiting resolution to groups of payers in tracing for statistical purposes; allowing limited different markings of payment instruments while preventing payers from learning which marking they receive; providing for recovery of lost money without compromise of unrelated transactions; allowing participants the ability to retain, not forward, and even destroy some tracing information without financial harm; providing the option of artificial increase in the computational cost of at least some tracing; and providing the option of blurry linking of payments to payers.

Claims

1. In a machine-implemented payment system method, the improvement comprising the steps of:

forming with an automated machine, signals representing tracing signals depending on tracing key data substantially concealed by at least one trustee party apparatus; and

convincing at least one party, while keeping the tracing key data secret from that party, that the tracing key data allows linking of payment data with data representing payer accounts;

such that without the tracing key data of the at least one trustee party apparatus it is infeasible to link payment transaction data with data representing payer accounts and that with the cooperation of the at least one trustee party apparatus using the tracing key data, at least under predetermined conditions, at least a predetermined linking is feasible.

2. In the improved method of claim 1, at least one party apparatus other than a trustee party apparatus being necessary to issue validated money.

3. In the improved method of claim 1, requiring for tracing participation of a predetermined number of trustee party apparatuses.

4. In the improved method of claim 1, including more than one tracing signal per payment.

5. In the improved method of claim 1, including different predetermined numbers of trustee party apparatuses for different tracing signals.

6. In the improved method of claim 1, storing for at least a substantial time at least one of said tracing signals by at least one system apparatus.

7. In the improved method of claim 1, preventing at least one of said tracing signals from being forwarded from at least one system apparatus to a further system apparatus.

8. In the improved method of claim 1, deleting parts of a encrypted tracing signal so that search for the deleted parts is substantially needed to recover the tracing signal.

9. In the improved method of claim 2, 3, 8, said machine-implemented system allowing said at least one trustee party apparatus to allow linking from a particular payer account to at least one particular payment transaction.

10. In the improved method of claim 9, developing information in the form of a blacklist of tracing signals that can be transferred from said at least one trustee party apparatus to a tracer party apparatus, without revealing other tracing information to the tracer party apparatus that is searched directly by the tracer party apparatus for a substantially identical matching tracing signal.

11. In the improved method of claim 9, developing information in the form of a witness signal that can be transferred from said at least one trustee party apparatus to a tracer party apparatus, without revealing other tracing information to that tracer party apparatus, that is used by the tracer party apparatus in a computational matching process.

12. In the improved method of claim 9, concealing from said at least one trustee party apparatus which payer account is being traced.

13. In the improved method of claim 9, cooperation of said at least one trustee party apparatus in computational testing of whether said payment transaction corresponds to a particular payer account.

14. In the improved method of claim 13, allowing said testing such that it remains infeasible for said at least one trustee party apparatus to transfer such testing ability to other parties'"'"' apparatus without transferring tracing signals.

15. In the improved method of claim 13, allowing said testing while concealing the identity of the payer account from said at least one trustee party apparatus.

16. In the improved method of claim 2, 3, 8, said system allowing at least one trustee party apparatus to allow a particular payment transaction to be traced to the corresponding payer account.

17. In the improved method of claim 16, allowing such tracing while concealing from said at least one trustee party apparatus the account identity.

18. In the improved method of claim 16, allowing such tracing while concealing from said at least one trustee party apparatus the payment transaction identity.

19. In the improved method of claim 2, 3, 8, grouping within said system at least some payer accounts into categories.

20. In the improved method of claim 19, concealing from the payer party apparatus the category in which a corresponding payer account is placed.

21. In the improved method of claim 19, using said groupings for analyzing patterns of plural payment transactions while concealing transaction details.

22. In the improved method of claim 2, 3, 8, payer parties'"'"' apparatuses cooperating within said system and maintaining data and making computations for conducting transactions.

23. In the improved method of claim 22, payer apparatuses using in payment transactions only tamper-resistant devices issued to use with them.

24. In the improved method of claim 22, payer apparatuses using in payment transactions only information processing equipment other than tamper-resistant devices issued to use with them.

25. In the improved method of claim 22;

payer apparatuses using in payment transactions both tamper-resistant devices issued to use with them and other information processing equipment; and

configuring the equipment so that, for at least some transactions, the tamper-resistant device only communicates to other parties'"'"' apparatus through said other information processing equipment.

42. In the improved method of claim 1:

storing for at least a substantial time at least one of said tracing signals by at least one system apparatus; and

preventing at least one of said tracing signals from being forwarded from at least one system apparatus to a further system apparatus.

26. In a machine-implemented blind signature system method, the improvement comprising the steps of:

forming at least part of one blinding signal from a restricted distribution that is dependent upon tracing information; and

convincing at least one party that at least the restricted distribution that is dependent upon tracing information substantially applies without revealing the at least part of the blinding signal to the at least one party.

27. In the method of claim 26, using signal protocols for cooperation of a party apparatus obtaining a blind signature and the party apparatus issuing the blind signature that ensure a blinding value be taken from a limited range.

28. In the method of claim 27 wherein said signal protocols achieve a blurred linking.

29. In the method of claim 27, wherein said signal protocols allow linkability.

30. In the method of claim 26, wherein said signal protocols are such that a computational test is performed by parties'"'"' apparatuses other than said party obtaining a blind signature to recognize a valid blinding value and thereby link payer accounts with payment transactions.

31. In the method of claim 30, wherein multiple such computationally distinguishable elements correspond to multiple predetermined numbers of trustee party apparatus.

32. In the method of claim 30, wherein multiple such computationally distinguishable elements correspond to multiple predetermined numbers of trustee party apparatus.

33. In the method of claim 30, including leaving out some information from at least one of said distinguishable blinding values to require additional computational testing and thereby increase the cost of testing.

37. In the method of claim 26, wherein parties'"'"' apparatuses cooperate in obtaining said blind signature, maintaining data and making computations for conducting transactions.

38. In the method of claim 37, including the step of system providers issuing to said parties'"'"' apparatus tamper-resistant devices and the steps of said parties'"'"' apparatuses using said tamper resistant devices for information processing in said cooperation.

39. In the method of claim 37, including the step of said parties'"'"' apparatus obtaining information processing means from a party apparatus other than one authorized by said system providers and using such means for conducting transactions in said cooperation.

40. In the method of claim 37, said parties'"'"' apparatus using in said cooperation both tamper-resistant devices authorized by said system provider party apparatus and other information processing equipment, and, for the purposes of at least some transaction within said cooperation communicating information from said tamper-resistant device only through said other information processing equipment.

34. In a machine-implemented blind signature system method, the improvement comprising the step of developing a blinding value in a reproducible computation that uses a seed key substantially known only to an account holder party.

35. In the method of claim 34, imparting a one-way property so that particular signal values can be given that allow computing forward blinding factors and the signal values given being such that it is substantially infeasible to use them to compute back to earlier factors.

36. In the method of claim 34, wherein the payment account holder party apparatus stores said seed key separately from the money number and later turns it in if the money number data should become lost.

41. In a payment system apparatus, the improvement comprising:

means for forming tracing signals dependent on tracing key data being substantially concealed by at least one trustee party apparatus; and

means for convincing at least one party, while keeping the tracing key data secret from that party, that the tracing key data allows linking of payment data with data representing payer accounts;

such that without the tracing key data of the at least one trustee party apparatus it is infeasible to link payment transaction data with payer accounts and that with the cooperation of the at least one trustee party apparatus using the tracing key data, at least under predetermined conditions, at least a predetermined linking is feasible.

43. In the apparatus of claim 41, means requiring at least one party apparatus other than a trustee party apparatus being necessary to issue validated money.

44. In the apparatus of claim 41, means for requiring tracing participation of a predetermined number of trustee party apparatuses.

45. In the apparatus of claim 41:

means for storing for at least a substantial time at least one of said tracing signals by at least one system apparatus; and

means for preventing at least one of said tracing signals from being forwarded from at least one system apparatus to a further system apparatus.

46. In the apparatus of claim 41, means for deleting parts of an encrypted tracing signal so that search for the deleted parts is substantially needed to recover the tracing signal.

47. In the apparatus of claim 43, 44, 45 or 46:

means for causing payer parties'"'"' apparatuses to cooperate within said system and to maintain data and to make computations for conducting transactions.

48. In the apparatus of claim 47,

means for causing said apparatuses to use in payment transactions only tamper-resistant devices issued for use with them.

49. In the apparatus of claim 47, means for causing payer apparatuses to use in payment transactions only information processing equipment other than tamper-resistant devices issued for use with them.

50. In the apparatus of claim 47:

means for causing payer apparatuses to use in payment transactions both tamper-resistant devices issued for use with them and other information processing equipment; and

means for configuring the equipment so that, for at least some transactions, the tamper-resistant device can only communicate to other parties'"'"' apparatus through said other information processing equipment.

51. In a payment system apparatus, the improvement comprising:

means for providing a blind signature type of signal associated with electronic payment data; and

means for forming at least part of one blinding signal from a restricted distribution that is dependent upon tracing information; and

means for convincing at least one party that at least the restricted distribution that is dependent upon tracing information substantially applies without revealing the at least part of the blinding signal to the at least one party.