Document modification detection and prevention

• US 7,735,144 B2
• Filed: 05/16/2003
• Issued: 06/08/2010
• Est. Priority Date: 05/16/2003
• Status: Active Grant

• Current Assignee: Adobe Inc.
• Original Assignee: Adobe Systems Incorporated (Adobe Inc.)
• Inventors: Agrawal, Sunil C., Pravetz, James D., Chaudhury, Krish
• Primary Examiner(s): Orgad; Edan
• Assistant Examiner(s): Tolentino; Roderick
• Application Number:
  US10/440,487
• Publication Number:
  US 20040230891A1
• Time in Patent Office: 2,580 Days
• Field of Search: 380/51, 713/176, 726/2, 726/21, 726/26, 726/27, 726/30, 726/33, 705/50, 705/51, 705/55, 705/56, 705/57, 705/58, 705/59
• US Class Current: 726/30
• CPC Class Codes: G06F 21/6218 to a system of files or objects, e.g. local or distributed file system or database
• CPC Class Codes: H04L 63/18 using different networks or channels, e.g. using out of band channels cryptographic mechanisms or cryptographic arrangements for key distribution involving distinctive intermediate devices or communication paths H04L9/0827; cryptographic mechanisms or cryptographic arrangements for authentication using a plurality of channels H04L9/3215
• CPC Class Codes: H04L 9/3247 involving digital signatures

Abstract

Methods and apparatus, including computer program products, implementing and using techniques for document authentication. An electronic document is presented to a user. The electronic document has data representing a signed state and a current state. A disallowed difference between the signed state and the current state is detected, based on one or more rules that are associated with the electronic document. A digital signature associated with the electronic document is invalidated in response to the detecting.

Claims

1. A computer implemented method, comprising:

reading an electronic document, the electronic document comprising content rules, an existing signed state, and existing content items;

authenticating the electronic document one or more times, each authenticating comprising;

classifying the existing content items of the electronic document into existing invariant content items and existing modifiable content items according to the content rules;

receiving one or more user actions for one or more of the existing content items;

determining whether the one or more user actions are permitted by the content rules;

reclassifying one or more existing modifiable content items into new invariant content items in response to the one or more user actions;

generating an object digest for an aggregation of the existing invariant content items and the new invariant content items by digesting the existing invariant content items and the new invariant content items, wherein the aggregation includes a simple content item, a semi-complex content item and a complex content item, the object digest is generated according to their complexity and generating the object digest includes ignoring one or more existing modifiable content items in the electronic document that are not reclassified into new invariant content items;

generating a saved state of the electronic document; and

adding a new signed state to the electronic document, the new signed state comprising the object digest, the saved state, and an electronic signature

wherein generating an object digest is preformed by a processor of an electronic document reader.

2. The method of claim 1, wherein the digesting is recursive on layers of content items in the electronic document.

3. The method of claim 1, wherein each of the content items in the electronic document has a type identifier and a length.

5. The method of claim 1, wherein the object digest is a hash.

6. The method of claim 1, wherein the saved state of the electronic document is a byte range digest.

7. The method of claim 6, wherein the byte range digest is a byte range hash generated for a saved version of the electronic document.

8. The method of claim 1, wherein the user actions are one or more of the following:

entering data into predefined fields of the electronic document or annotating the electronic document.

9. The method of claim 1, further comprising:

invalidating the new signed state if the one or more user actions are not permitted by the content rules.

10. The method of claim 1, the authenticating further comprising:

saving the electronic document with the new signed state to a computer-readable medium.

11. The method of claim 1, wherein the semi-complex content item is a form field.

12. The method of claim 1, wherein:

the content rules state that a first user action of a first signature causes a first subset of the existing modifiable content items to be reclassified into new invariant content items and a user action of a second signature causes a second subset of the existing modifiable content items is reclassified into new invariant content items;

the first signature is not a part of the first subset of the existing modifiable content items;

the second signature is not a part of the second subset of the existing modifiable content items; and

the first subset of the existing modifiable content items does not overlap the second subset of the existing modifiable content items.

4. The method of 3, wherein the object digest contains the type identifier and the length of each content item.

13. A computer readable storage device storing a computer program which, when executed by a computer processor, causes the computer processor to perform operations comprising:

reading an electronic document, the electronic document comprising content rules, an existing signed state, and existing content items;

authenticating the electronic document one or more times, each authenticating comprising;

classifying the existing content items of the electronic document into existing invariant content items and existing modifiable content items, according to the content rules;

receiving one or more user actions for one or more of the existing content items;

determining whether the one or more user actions are permitted by the content rules;

reclassifying one or more existing modifiable content items into new invariant content items in response to the one or more user actions;

generating an object digest for an aggregation of the existing invariant content items and the new invariant content items, wherein the aggregation includes a simple content item, a semi-complex content item and a complex content item, and the object digest is generated by digesting the existing invariant content items and the new invariant content items according to their complexity and generating the object digest includes ignoring one or more existing modifiable content items in the electronic document that are not reclassified into new invariant content items;

generating a saved state of the electronic document; and

adding a new signed state to the electronic document, the new signed state comprising the object digest, the saved state, and an electronic signature.

14. The storage device of claim 13, wherein the digesting is recursive on layers of content items in the electronic document.

15. The storage device of claim 13, wherein each of the content items of the electronic document has a type identifier and a length.

17. The storage device of claim 13, wherein the object digest is a hash.

18. The storage device of claim 13, wherein the saved state of the electronic document is a byte range digest.

19. The storage device of claim 18, wherein the byte range digest is a byte range hash generated for a saved version of the electronic document.

20. The storage device of claim 13, wherein the user actions are one or more of the following:

entering data into predefined fields of the electronic document or annotating the electronic document.

21. The storage device of claim 13, the operations further comprising:

invalidating the new signed state if the one or more user actions are not permitted by the content rules.

22. The storage device of claim 13, the authenticating further comprising:

saving the electronic document with the new signed state to a computer-readable medium.

23. The storage device of claim 13, wherein the semi-complex content item is a form field.

24. The storage device of claim 13, wherein:

the content rules state that a first user action of a first signature causes a first subset of the existing modifiable content items to be reclassified into new invariant content items and a user action of a second signature causes a second subset of the existing modifiable content items is reclassified into new invariant content items;

the first signature is not a part of the first subset of the existing modifiable content items;

the second signature is not a part of the second subset of the existing modifiable content items; and

the first subset of the existing modifiable content items does not overlap the second subset of the existing modifiable content items.

16. The storage device of 15, wherein the object digest contains the type identifier and the length of each content item.

25. A system comprising a computer readable storage device storing a computer program, a display device, and one or more processors operable to interact with the display device and to execute the computer program and perform operations comprising:

reading an electronic document, the electronic document comprising content rules, an existing signed state, and existing content items;

authenticating the electronic document one or more times, each authenticating comprising;

classifying the existing content items of the electronic document into existing invariant content items and existing modifiable content items, according to the content rules;

receiving one or more user actions for one or more of the existing one or more content items;

determining whether the one or more user actions are permitted by the content rules;

reclassifying one or more existing modifiable content items into new invariant content items in response to the one or more user actions;

generating an object digest for an aggregation of the existing invariant content items and the new invariant content items by digesting the existing invariant content items and the new invariant content items, wherein the aggregation includes a simple content item, a semi-complex content item and a complex content item, the object digest is generated according to their complexity and generating the object digest includes ignoring one or more existing modifiable content items in the electronic document that are not reclassified into new invariant content items;

generating a saved state of the electronic document; and

adding a new signed state to the electronic document, the new signed state comprising the object digest, the saved state, and an electronic signature.

26. The system of claim 25, wherein the digesting is recursive on layers of content items in the electronic document.

27. The system of claim 25, wherein each of the content items of the electronic document has a type identifier and a length.

29. The system of claim 25, wherein the object digest is a hash.

30. The system of claim 25, wherein the saved state of the electronic document is a byte range digest.

31. The system of claim 30, wherein the byte range digest is a byte range hash generated for a saved version of the electronic document.

32. The system of claim 25, wherein the user actions are one or more of the following entering data into predefined fields of the electronic document or annotating the electronic document.

33. The system of claim 25, the operations further comprising:

invalidating the new signed state if the one or more user actions are not permitted by the content rules.

34. The system of claim 25, the authenticating further comprising:

saving the electronic document with the new signed state to a computer-readable medium.

35. The system of claim 25, wherein the semi-complex content item is a form field.

36. The system of claim 25, wherein:

the content rules state that a first user action of a first signature causes a first subset of the existing modifiable content items to be reclassified into new invariant content items and a user action of a second signature causes a second subset of the existing modifiable content items is reclassified into new invariant content items;

the first signature is not a part of the first subset of the existing modifiable content items;

the second signature is not a part of the second subset of the existing modifiable content items; and

the first subset of the existing modifiable content items does not overlap the second subset of the existing modifiable content items.

28. The system of 27, wherein the object digest contains the type identifier and the length of each content item.