How to create PADES using offline signature and OCSP response

I'm stumped trying to figure out Esig DSS java suite just from docs and source. (eu.europa.esig.dss.* tree)

We connect to Swedish BankID to sign PDF's and simple plain texts. Response is a SOAP XML with fields for the signature and an OCSP response.

The end goal is to combine these two parts into a single object "a valid signature" that can be embedded in a PDF (using DSS and PDFbox).

The contents of the BankID Soap fields seems to have the right format for DSS tools:

The signature can be loaded with

DSSDocument sigDoc = new InMemoryDocument(xmlSignature)
SignedDocumentValidator documentValidator = SignedDocumentValidator.fromDocument(sigDoc);
// ...
AdvancedSignature advancedSignature = documentValidator.getSignatures().get(0);

and the OCSP response can be read with

ExternalResourcesOCSPSource source = new ExternalResourcesOCSPSource(ocspBytes);
BasicOCSPResp basicOCSPResp = source.getContainedOCSPResponses().get(0);

I can print out various info from the objects, find embedded certificates etc, so the format seems legit.

Question: How do I get a valid OCSPToken from the ExternalResourcesOCSPSource?

I keep running in circles trying to combining the two into a single AdvancedSignature (if that's what I can use to embed into a PDF).

Solution

An advanced digital signature provided by a third system can not be used to create a valid signed PDF

A PAdES signature is always enveloped into a PDF document, so it is not possible for the signature service to be returning a detached PAdES signature that is considered valid by DSS.

It probably provides a detached CAdES or XAdES signature into the SOAP message that can be processed by DSS( DSS provides a high level API to sign documents using XAdES, CAdES, PAdES and aSiCS formats).

Both formats support embedding the OCSP responses, but it requires to add a TimeStamp too, which make more difficult to build the final format. It could be the reason to use a custom field into the SOAP message to return the OCSP response

XAdES and PAdES are conceptually similar but structurally different. A XAdES signature is XML and PAdES is binary. A XML signature can not be converted to PAdES

PAdES and CAdES use CMS, both are binary and they use ASN.1 syntax. But the signed message is different, CAdES signature is calculated on the entire document (and some othe attributes) and PAdes use certain data of the PDF document. Therefore a cades signature could not be converted to PAdes either.