Electronic signature management system

• US 6,307,955 B1
• Filed: 12/18/1998
• Issued: 10/23/2001
• Est. Priority Date: 12/18/1998
• Status: Expired due to Term

• Current Assignee: Topaz Systems Inc
• Original Assignee: Topaz Systems Inc
• Inventors: Zank, Anthony E., Stevens, David R.
• Primary Examiner(s): Au, Amelia M.
• Assistant Examiner(s): Dastouri, Mehrdad
• Application Number:
  US09/216,246
• Time in Patent Office: 1,040 Days
• Field of Search: 382/187, 382/188, 382/189, 382/200, 382/201, 382/218, 382/219, 382/116, 382/119, 382/120, 382/121, 382/122, 382/123, 713/170, 713/176, 713/187, 380/30, 380/282
• US Class Current: 382/121
• CPC Class Codes: G06V 40/30 Writer recognition; Reading and verifying signatures

Abstract

An electronic signature management system includes a graphic tablet digitizer for signaling position coordinates of a stylus being moved to produce a handwritten signature, a clock circuit of the digitizer defining a fixed interval between successive stylus position measurements, a computer processor electrically interfaced with the tablet and programmed for receiving and storing a multiplicity of the coordinates in sequential order as an electronic signature forming a time history of the stylus movement. The computer is also programmed for verifying the fixed time intervals of the measurements, such as by comparing a ratio of total elapsed time and total number of the measurements with a standard measurement interval, and for comparing the electronic signature with a reference signature, such as by feeding a stored reference signature counterpart and the electronic signature into a cross-correlator for evaluating a degree of correspondence between respective time histories of the electronic signature and the reference signature. The signatures can also be compared visually in a simultaneous display wherein respective pointers follow the signatures orthogonally in response to an operator-controlled slider, with pertinent data corresponding to the pointer positions being displayed. The electronic signature is preferably encrypted using a hash function or message digest of the document as a key. Also disclosed are methods for electronically signing a document, wherein the electronic signature is electronically bound to the document, wherein the electronic signature is encrypted using a key derived from the document and not saved, and methods for decrypting and verifying electronic signatures.

Claims

1. A system for managing handwritten signatures, comprising:

(a) a graphic tablet for signaling position coordinates of a stylus during manual movement thereof relative to a writing surface;

(b) a clock circuit for periodically initiating position measurements by the graphic tablet at predetermined fixed time intervals;

(c) a first computer processor electrically interfaced with the tablet, the processor being programmed for receiving a multiplicity of the coordinates during the manual movement of the stylus, and storing respective sets of the coordinates in sequential order as an electronic signature while preserving a time relation between coordinates, the electronic signature forming a time history of the stylus movement; and

(d) means for comparing the electronic signature with a reference signature, comprising the computer processor having a graphic display implemented for simultaneously displaying the electronic signature and the reference signature with corresponding cursors being positioned along a line segment of the signature and oriented perpendicular to the line segment, and the computer being further implemented for moving the cursors in response to operator input.

2. The system of claim 1, wherein the means for comparing further comprises reference memory for storing an electronic counterpart of the reference signature, and a cross-correlator for evaluating a degree of correspondence between respective time histories of the electronic signature and the electronic counterpart of the reference signature.

3. The system of claim 2, wherein the reference memory is electronically interfaced with the first computer processor.

4. The system of claim 1, wherein the electronic signature has associated therewith a date and time of the handwritten signature.

5. The system of claim 4, wherein the electronic signature has further associated therewith an annotation including at least one of a geographic location, a physical address, and an identification string.

6. The system of claim 1, wherein the first computer processor is a digital processor, and the electronic signature is a digital signature.

7. The system of claim 1, wherein the computer is further programmed for encrypting the time history to a fixed key of arbitrary length, the stored electronic signature being in encrypted form.

8. The system of claim 7, wherein the computer is programmed for generating the key as a cryptographic hash function or message digest of the document.

9. The system of claim 1, wherein the computer processor is further implemented for determining a stylus velocity associated with each line segment, and displaying the line segments at widths being proportional to the stylus velocity.

10. The system of claim 1, wherein the computer processor is programmed for displaying the line segments at widths being proportional to the stylus pressure data.

11. A system for managing handwritten signatures, comprising:

(a) a graphic tablet for signaling position coordinates of a stylus during manual movement thereof relative to a writing surface;

(b) a clock circuit in the graphic tablet for periodically initiating position measurements by the graphic tablet at predetermined fixed time intervals;

(c) a first computer processor electrically interfaced with the tablet, the processor being programmed for receiving a multiplicity of the coordinates during the manual movement of the stylus, and storing respective sets of the coordinates in sequential order as an electronic signature while preserving a time relation between coordinates, the electronic signature forming a time history of the stylus movement; and

(d) means for verifying the fixed time intervals of the measurements, comprising the computer being programmed for determining a ratio of a total elapsed time of the measurements and a total number of the measurements, and comparing the ratio with the predetermined interval.

12. The system of claim 11, wherein the time intervals are not greater than 20 milliseconds.

13. The system of claim 12, wherein the time intervals are between 2 milliseconds and 3 milliseconds.

14. The system of claim 11, wherein the means for verifying the time intervals comprises:

(a) the clock circuit having a certified unalterable time interval;

(b) the tablet being implemented for transmitting an encoded certification stamp with the coordinate data; and

(c) the computer being programmed for decoding the certification stamp to verify use of the certified time interval.

15. The system of claim 11, wherein the first computer processor is a digital processor, and the electronic signature is a digital signature.

16. The system of claim 11, wherein the computer is further programmed for encrypting the time history to a fixed key of arbitrary length, the stored electronic signature being in encrypted form.

17. The system of claim 16, wherein the computer is programmed for generating the key as a cryptographic hash function or message digest of the document.

18. A method for verifying the signature of an electronically signed a document having associated therewith an electronic signature being a stored sequence of data corresponding to coordinates of stylus movement producing a first handwritten signature:

(a) capturing a second electronic signature as a stored sequence of data corresponding to coordinates of stylus movement producing second handwritten signature;

(b) simultaneously displaying in locational proximity graphic counterparts of the first and second electronic signatures;

(c) displaying, for each of the graphic counterparts, a cursor being positioned along a line segment of the signature and oriented perpendicular to the line segment; and

(d) for each of the graphic counterparts, moving the cursor relative to the signature in response to operator input.

19. The method of claim 18, comprising, for each of the graphic counterparts the further steps of:

(a) determining at least one measurement parameter relative to the line segment at which the cursor is located; and

(b) displaying a digital representation of the parameter.

20. The method of claim 19, wherein the at least one measurement parameter is selected from the group consisting of a point number, a stroke number, an acceleration value, and a pressure value.

21. A system for managing handwritten signatures, comprising:

(a) a graphic tablet for signaling position coordinates of a stylus during manual movement thereof relative to a writing surface;

(b) a computer processor electrically interfaced with the tablet, the processor being programmed for receiving a multiplicity of the coordinates during the manual movement of the stylus, and storing respective sets of the coordinates in sequential order as an electronic signature while preserving a time relation between coordinates, the electronic signature forming a time history of the stylus movement; and

(c) means for comparing the electronic signature with a reference signature, comprising the computer processor having a graphic display implemented for simultaneously displaying the electronic signature and the reference signature with corresponding cursors being positioned along a line segment of the signature and oriented perpendicular to the line segment, and the computer being further implemented for moving the cursors in response to operator input.

22. The system of claim 21, wherein the electronic signature includes recorded stylus pressure data, the system further comprising means for varying a displayed line width of each line segment of the electronic signature and the reference signature, the computer processor being further implemented for displaying the line segments of the electronic signature at widths being proportional to the stylus pressure data.

23. The system of claim 21, the system further comprising means for varying a displayed line width of each line segment of the electronic signature and the reference signature, the computer processor being further implemented for determining a stylus velocity associated with each line segment of the electronic signature, and displaying the line segments of the electronic signature at widths being proportional to the stylus velocity.

24. A system for managing handwritten signatures, comprising:

(a) a graphic tablet for signaling position coordinates of a stylus during manual movement thereof relative to a writing surface;

(b) a computer processor electrically interfaced with the tablet, the processor being programmed for receiving a multiplicity of the coordinates during the manual movement of the stylus, and storing respective sets of the coordinates in sequential order as an electronic signature while preserving a time relation between coordinates, the electronic signature forming a time history of the stylus movement, the computer processor having a graphic display implemented for displaying the electronic signature as sequential line segments; and

(c) the computer processor being further implemented for determining a stylus velocity associated with each line segment, and displaying the line segments at widths being proportional to the stylus velocity.

25. A system for managing handwritten signatures, comprising:

(a) a graphic tablet for signaling position coordinates and stylus pressure data of a stylus during manual movement thereof relative to a writing surface;

(b) a computer processor electrically interfaced with the tablet, the processor being programmed for receiving a multiplicity of the coordinates and the stylus pressure data during the manual movement of the stylus, and storing respective sets of the coordinates with the stylus pressure data in sequential order as an electronic signature, the electronic signature forming a time history of the stylus movement and pressure, the computer processor having a graphic display implemented for displaying the electronic signature as sequential line segments; and

(c) the computer processor being further implemented for displaying the line segments at widths being proportional to the stylus pressure data.

26. A method for authenticating a document having been signed by a method comprising capturing a handwritten signature as a sequence of data corresponding to coordinates of stylus movement producing the signature, storing the data as an electronic signature, creating a signature receipt as a cryptographic hash function or message digest of the electronic signature, creating a signature encryption key by generating a cryptographic hash function or message digest of a stored counterpart of the document, encrypting the electronic signature using the signature encryption key, creating a document receipt as a cryptographic hash function or message digest of a stored counterpart of the document, producing counterparts of the signature and document receipts, and encapsulating the signature and document receipts in a digital signature, the method comprising the further steps of:

(a) transmitting the digital signature containing the signature and document receipts to a signer of the document;

(b) recalling the transmitted digital signature

(c) extracting the signature and document receipts from the digital signature;

(d) recovering the electronic signature and a stored counterpart of the document;

(e) generating new signature and document receipts from the recovered electronic signature and the stored counterpart of the document; and

(f) comparing the recovered signature and document receipts with the new signature and document receipts, the document being authenticated when respective receipt counterparts are matching.

27. The method system of claim 26, comprising the further steps of identifying stored instances of the signature encryption key and erasing each such instance.

28. A method for authenticating a document having been signed by a method comprising capturing a handwritten signature as a sequence of data corresponding to coordinates of stylus movement producing the signature, storing the data as an electronic signature, creating a signature receipt as a cryptographic hash function or message digest of the electronic signature, creating a signature encryption key by generating a cryptographic hash function or message digest of a stored counterpart of the document, encrypting the electronic signature using the signature encryption key, creating a document receipt as a cryptographic hash function or message digest of a stored counterpart of the document, and producing counterparts of the signature and document receipts, the method comprising the further steps of:

(a) distributing plural counterparts of the signature and document receipts to signers of the document;

(b) recalling the distributed signature and document receipts; and

(c) comparing the recalled signature receipts and the document receipts, the document being authenticated when respective receipt counterparts are matching.

29. The method of claim 28, comprising the further step of encapsulating the signature and document receipts in a digital signature.

30. The method system of claim 28, comprising the further steps of identifying stored instances of the signature encryption key and erasing each such instance.

31. A method for authenticating a document having been signed by a method comprising capturing a handwritten signature as a sequence of data corresponding to coordinates of stylus movement producing the signature, storing the data as an electronic signature, creating a signature receipt as a cryptographic hash function or message digest of the electronic signature, creating a signature encryption key by generating a cryptographic hash function or message digest of a stored counterpart of the document, encrypting the electronic signature using the signature encryption key, creating a document receipt as a cryptographic hash function or message digest of a stored counterpart of the document, and producing counterparts of the signature and document receipts, the method comprising the further steps of:

(a) delivering the signature and document receipts to a signer of the document;

(b) recalling the signature and document receipts;

(c) recovering the electronic signature and a stored counterpart of the document;

(d) generating new signature and document receipts from the recovered electronic signature and the stored counterpart of the document; and

(e) comparing the recalled signature and document receipts with the new signature and document receipts, the document being authenticated when respective receipt counterparts are matching.

32. The method of claim 31, comprising the further step of encapsulating the electronic signature in a digital signature.

33. The method system of claim 31, comprising the further steps of identifying stored instances of the signature encryption key and erasing each such instance.