Verifying integrity of physical documents

1. An apparatus comprising:

a processor;

a memory that stores code executable by the processor to:

identify an integrity symbol within a physical document, the integrity symbol representative of content of the physical document;

convert the integrity symbol into a first integrity map containing a plurality of content values, the integrity symbol being a symbolic representation of the first integrity map suitable for printing; and

verify integrity of the physical document, by:

generating a second integrity map from the physical document using the content of the physical document, the second integrity map also containing a plurality of content values; and

comparing the first integrity map and the second integrity map to verify integrity of the physical document.

2. The apparatus of claim 1 , further comprising an imager that creates a digital image of the physical document, wherein identifying an integrity symbol within a physical document comprises the processor recognizing the integrity symbol within the digital image.

3. The apparatus of claim 1 , wherein the first integrity map includes a plurality of values wherein generating the second integrity map from the physical document comprises the processor:

identifying a plurality of content areas in the physical document, each region containing content;

creating a table having a number of entries equal to a number of content areas in the physical document;

determining, for each content area, whether a content area is complete;

populating an entry in the table corresponding to a content area with a null value in response to the content area being incomplete; and

populating an entry in the table corresponding to a content area with a cryptographic hash value of the content in that content area in response to the content area being complete.

4. The apparatus of claim 1 , wherein the processor further:

encodes the second integrity map to form a second integrity symbol; and

inserts the second integrity symbol into a digital image formed from the physical document, the second integrity symbol being a symbolic representation of the second integrity map suitable for printing.

5. The apparatus of claim 4 , wherein inserting the second integrity symbol into the digital image comprises appending the second integrity symbol to the identified integrity symbol.

6. The apparatus of claim 1 , wherein the integrity map comprises a plurality of entries corresponding to a plurality of content areas of the physical document, at least one content area of the physical document being an incomplete area, and wherein an integrity map entry corresponding to the incomplete area contains a null value.

7. The apparatus of claim 6 , wherein comparing content of the physical document to the integrity map to verify integrity of the physical document comprises the processor:

identifying an entry in the integrity map having a null value;

identifying a region of the physical document that corresponds to the entry;

determining whether a change has occurred to the region; and

performing, in response to a change having occurred, an action selected from the group consisting of: ignoring the change, notifying the user of the change, and signaling invalidation of the physical document.

8. The apparatus of claim 1 , wherein the physical document contains a plurality of content areas and wherein the integrity map comprises a hash table, each entry in the hash table containing a hash value calculated from content in one of the content areas, the hash value being an output of a cryptographic hash function.

9. A method comprising:

identifying, by use of a processor, an integrity symbol within a physical document, the integrity symbol representative of content of the physical document;

converting the integrity symbol into an integrity map, the integrity symbol being a symbolic representation of the integrity map suitable for printing; and

comparing content of the physical document to the integrity map to verify integrity of the physical document, wherein the physical document contains a plurality of content areas corresponding to a plurality of values in the integrity map, the content areas including at least one completed area and at least one incomplete area, wherein comparing content of the physical document to the integrity map to verify the integrity of the physical document comprises the processor ignoring the at least one incomplete area.

10. The method of claim 9 , further comprising:

creating a digital image of the physical document, wherein identifying an integrity symbol within a physical document comprises recognizing the integrity symbol within the digital image.

11. The method of claim 9 , wherein the integrity map comprises a plurality of entries corresponding to the plurality of content areas of the physical document, wherein a integrity map entry corresponding to each incomplete content area contains a null value.

12. The method of claim 11 , wherein comparing content of the physical document to the integrity map to verify integrity of the physical document comprises:

identifying an entry in the integrity map having a null value;

identifying a region of the physical document that corresponds to the entry;

determining whether a change has occurred to the region; and

performing, in response to a change having occurred, an action selected from the group consisting of: ignoring the change, notifying the user of the change, and signaling invalidation of the physical document.

13. The method of claim 11 , wherein the integrity symbol encodes one or more extents corresponding to a location in the physical document of the at least one incomplete content area and further encodes one or more extents corresponding to a location in the physical document of the at least one completed content area.

14. The method of claim 9 , wherein the integrity map is a first integrity map and wherein comparing content of the physical document to the integrity map to verify integrity of the physical document comprises:

generating a second integrity map from the physical document using the plurality of content areas of the physical document; and

comparing the first integrity map and the second integrity map to verify integrity of the physical document.

15. The method of claim 14 , wherein generating the second integrity map from the physical document comprises:

creating a table having a number of entries equal to a number of content areas in the physical document;

populating an entry in the table corresponding to an incomplete content area with a null value in response to the content area being incomplete; and

populating an entry in the table corresponding to a completed content area with a cryptographic hash value of the content in that content area.

16. A program product comprising a computer readable storage medium that stores code executable by a processor, the executable code comprising code to perform:

identifying an integrity symbol within a physical document, the integrity symbol representative of content of the physical document;

converting the integrity symbol into a first integrity map having a plurality of values, the integrity symbol being a graphical representation of the first integrity map suitable for printing;

generating a second integrity map from the physical document; and

comparing the first integrity map and the second integrity map to verify integrity of the physical document, wherein the physical document contains a plurality of content areas corresponding to a plurality of values in the first integrity map, the content areas including at least one completed area and at least one incomplete area, wherein comparing content of the physical document to the first integrity map and the second integrity map to verify the integrity of the physical document comprises ignoring the at least one incomplete area.

17. The program product of claim 16 , wherein the code further performs:

creating a digital image of the physical document, wherein identifying an integrity symbol within a physical document comprises recognizing the integrity symbol within the digital image.

18. The program product of claim 17 , wherein the code further performs:

encoding the second integrity map to form a second integrity symbol; and

inserting the second integrity symbol into the digital image, the second integrity symbol being a symbolic representation of the second integrity map suitable for printing.

19. The program product of claim 18 , wherein inserting the second integrity symbol into the digital image comprises appending the second integrity symbol to the identified integrity symbol.