How to check for digital signature information in an excel file

[Dhananjay Nene <dh...@vayana.in>]

This query pertains to both XSSF and HSSF type Excel files. I have been
struggling to figure out how to

a) Detect that a XLS / XLSX file has been digitally signed. and
b) Extract information about the signature

I see classes like PackageDigitalSignature and PackageDigitalSignature
manager (at least for the openxml4j files). However after a fair amount of
reading of the documents and search I am unable to figure out how to use
them (or other associated classes) to achieve the two objectives I laid out
above.

Any assistance / pointers to information that I could further build upon
would be greatly appreciated.

Dhananjay