I am digitally signing a PDF with iText7 and GlobalSign DSS. I implemented the GlobalSing DSS API calls into the necessary iText classes. I get the proper server responses and I am able to call the pdfSigner.signDetached() method with all the needed arguments. Signing with the pdfSigner also succeeds and I get a signed PDF that looks good at first sight. But when I open the signed pdf in Adobe Reader it tells me that the trust chain of the signing certificate is broken and that it can not trace it back to the CA root. Which is strange because it is an AATL certificate and the AATL list of the Adobe Reader is up to date.
And I do not understand why this is happening.
This is what I do :
call DSS for an identity : returns an id string, the signing certificate and an ocsp response
call DSS for the trustchain : returns the chain of certificates used to
sign the signing certicate, up to the GlobalSign root, together with
their oscp responses (except for the root)I create an array of X509Certificate objects containing the signing
certificate, 2 intermediates and the GlobalSign root certificate (in that order)I implement an IOcspClient that uses the ocsp response from the DSS call for the identity
I implement an ITsaClient that calls the DSS API /timestamp/{digest}
and finally I execute : pdfSigner.signDetached(externalDigest, externalSignature, chain.toArray(new X509Certificate[]{}), null, dssOcspClient, dssTSAClient, 0, PdfSigner.CryptoStandard.CMS);
in which the externalSignature (an implementation of IExternalSignature) will call the DSS identity/{id}/sign/{digest} API
While debugging into the signDetached method and deeper into the pdfSigner code, I clearly see that all certificates are in the chain in the right order. I see them being processed in the PdfPKCS7 class (however I don't know/understand exactly what is going on there). I see the signing taking place, no exceptions are thrown and at the end the produced PDF looks like it is correctly signed. Which Adobe says is not.
What am I missing here ?
The trustchain response from de DSS API not only returns the certificates from the chain of trust of the signing certificate, but also the ocsp responses for the two intermediates between the signing certificate and the GlobalSign root. These are never used. And in fact I don't know what to do with them either.
Could these be the missing pieces for AdobeReader to reconstruct the trust chain up to the GlobalSign root ?
And if so : how do I put them into that PDF ?
And if not : then what am I doing wrong that breaks that trustchain ?
An answer to these questions would save my day :-)
Here is the link to a PDF that will show the problem :
test pdf signed with DSS
(after accepting the answer, I removed the example pdf on my client's request)
Below are some pieces of the code.
The center piece that gathers the DSS info and calls the signDetached method
private InputStream sign(byte[] unsignedDocument) throws IOException, DssServiceException, GeneralSecurityException {
SigningIdentity signingIdentity = signingIdentityService.getValidSigningIdentity();
DssOcspClient dssOcspClient = new DssOcspClient(signingIdentity);
TrustChainResponse trustChainResponse = digitalSigningService.getTrustChain();
List<X509Certificate> chain = new ArrayList<>();
chain.add(signingIdentity.getCertificate());
chain.addAll(trustChainResponse.getTrustChain());
IExternalDigest externalDigest = new ProviderDigest(BC_SECURITY_PROVIDER);
IExternalSignature externalSignature = new DssExternalSignature(signingIdentity.getIdentity(), digitalSigningService);
ByteArrayOutputStream signedPdfOut = new ByteArrayOutputStream();
PdfSigner pdfSigner = createPdfSigner(new ByteArrayInputStream(unsignedDocument), signedPdfOut);
pdfSigner.signDetached(externalDigest, externalSignature, chain.toArray(new X509Certificate[]{}), null, dssOcspClient, dssTSAClient, 0, PdfSigner.CryptoStandard.CADES);
return new ByteArrayInputStream(signedPdfOut.toByteArray());
}
The IExternalSignature implementation
@Override
public byte[] sign(byte[] message) throws GeneralSecurityException {
MessageDigest messageDigest = new BouncyCastleDigest().getMessageDigest(DEFAULT_DIGEST_ALGORITHM);
byte[] documentHash = messageDigest.digest(message);
try {
return digitalSigningService.getSignature(signingIdentity, documentHash);
}
catch (DssServiceException e) {
LOGGER.error("error getting signature", e);
throw new GeneralSecurityException(e);
}
}
The IOcspClient implementation
@Override
public byte[] getEncoded(X509Certificate checkCert, X509Certificate issuerCert, String url) {
try {
if(Objects.equals(signingIdentity.getCertificate(), checkCert)) {
OCSPResp response = new OCSPResp(signingIdentity.getOcsp());
BasicOCSPResp basicResponse = (BasicOCSPResp)response.getResponseObject();
return basicResponse.getEncoded();
}
}
catch (CertificateException | IOException | OCSPException e) {
LOGGER.warn("OCSP validatie gefaald!", e.getMessage());
}
return null;
}
The ITSAClient implementation
@Override
public byte[] getTimeStampToken(byte[] imprint) throws Exception {
String digestAlgorithmOID = DigestAlgorithms.getAllowedDigest(DEFAULT_DIGEST_ALGORITHM);
ASN1ObjectIdentifier digestAlgOID = new ASN1ObjectIdentifier(digestAlgorithmOID);
AlgorithmIdentifier algID = new AlgorithmIdentifier(digestAlgOID, DERNull.INSTANCE);
MessageImprint messageImprint = new MessageImprint(algID, imprint);
byte[] hash = messageImprint.getHashedMessage();
return digitalSigningService.getTimeStamp(hash);
}
