How to digitally sign a PDF using X.509 certificate data from an iOS application

Question

I am creating a PDF in my application. I want to provide the best protection for these PDF files created through my application. I have added default security options provided by Apple, such as owner password, allow copying, allow printing, etc.

But I would like to add my certificate information or call it the signature number in pdf format using user certificate certificates (X.509).

Does security help? or How can this be achieved?

Answer 1

Unfortunately, iOS doesn't seem to provide this feature natively . Finding a library that will apply a digital signature to a PDF document is difficult, as many tools use handwritten signature images. It seems that there is no C or Objective-C that you could use on iOS, most implementations are in Java or C # or not available on iPhone (like Acrobat SDK or PLOP DS ).

You can nevertheless implement your own digital signature , it is quite simple and documented . You will need to serialize the PDF document, as indicated in this document, make a place for the signature object (this requires minimal analysis of the PDF layout), then calculate the signature and save it in a file.

For the cryptographic part, it seems that the Security Framework does not provide an API for creating the required PKCS # 7 signature. Thus, you can use OpenSSL instead.