Computer-implemented method and system for embedding and authenticating ancillary information in digitally signed content

1. A method comprising:

loading digital content containing a digitally signed portion into memory for processing, while checking for the integrity of a digital signature and the contents of the digitally signed portion;

identifying, by use of a processor, an existing digital signature block and an existing digital signature size block in a digitally signed file header of the digitally signed portion;

obtaining a digital signature size value from the digital signature size block, the digital signature size value corresponding to the size of the digital signature block plus the length of an ancillary data block plus a pre-determined pad;

authenticating the integrity of the digitally signed portion using the digital signature while processing the digital content;

unwrapping a purchase mechanism built into a wrapper associated with the digital content; and

extracting from the ancillary data block, by use of the processor, data referenced by instructions of the purchase mechanism, the extracting being performed without invalidating the digital signature.

2. The method as claimed in claim 1 wherein the ancillary data block and the pre-determined pad regions of the digital content include regions past the end of the last section of the digital content.

3. The method as claimed in claim 1 including verifying that a checksum field in a header of the digital content matches an image file checksum.

4. The method as claimed in claim 1 including verifying that the digital signature actually fills the whole space allocated to the digital signature in an attribute certificate table.

5. The method as claimed in claim 1 wherein the digital content is a file.

6. The method as claimed in claim 1 wherein the digital content is a digital transmission.

7. An article of manufacture embodied in a non-transitory machine storage medium including data that, when accessed by a machine, causes the machine to:

load digital content containing a digitally signed portion into memory for processing, while checking for the integrity of a digital signature and the contents of the digitally signed portion;

identify an existing digital signature block and an existing digital signature size block in a digitally signed file header of the digitally signed portion;

obtain a digital signature size value from the digital signature size block, the digital signature size value corresponding to the size of the digital signature block plus the length of an ancillary data block plus a pre-determined pad;

authenticate the integrity of the digitally signed portion using the digital signature while processing the digital content;

unwrap a purchase mechanism built into a wrapper associated with the digital content; and

extract from the ancillary data block data referenced by instructions of the purchase mechanism, the article of manufacture being configured to extract the data without invalidating the digital signature.

8. The article of manufacture as claimed in claim 7 wherein the ancillary data block and the pre-determined pad regions of the digital content include regions past the end of the last section of the digital content.

9. The article of manufacture as claimed in claim 7 being further configured to verify that a checksum field in a header of the digital content matches an image file checksum.

10. The article of manufacture as claimed in claim 7 being further configured to verify that the digital signature actually fills the whole space allocated to the digital signature in an attribute certificate table.

11. The article of manufacture as claimed in claim 7 wherein the digital content is a file.

12. The article of manufacture as claimed in claim 7 wherein the digital content is a digital transmission.

13. A system comprising:

a processor;

a memory in data communication with the processor; and

a content distribution system, executable by the processor, configured to:

load digital content containing a digitally signed portion into the memory for processing, while checking for the integrity of a digital signature and the contents of the digitally signed portion;

identify an existing digital signature block and an existing digital signature size block in a digitally signed file header of the digitally signed portion;

obtain a digital signature size value from the digital signature size block, the digital signature size value corresponding to the size of the digital signature block plus the length of an ancillary data block plus a pre-determined pad;

authenticate the integrity of the digitally signed portion using the digital signature while processing the digital content;

unwrap a purchase mechanism built into a wrapper associated with the digital content; and

extract from the ancillary data block data referenced by instructions of the purchase mechanism, the article of manufacture being configured to extract the data without invalidating the digital signature.

14. The system as claimed in claim 13 wherein the ancillary data block and the pre-determined pad regions of the digital content include regions past the end of the last section of the digital content.

15. The system as claimed in claim 13 being further configured to verify that a checksum field in a header of the digital content matches an image file checksum.

16. The system as claimed in claim 13 being further configured to verify that the digital signature actually fills the whole space allocated to the digital signature in an attribute certificate table.

17. The system as claimed in claim 13 wherein the digital content is a file.

18. The system as claimed in claim 13 wherein the digital content is a digital transmission.