Signing PDF with itextsharp and CSP

Juan Manuel Diaz

Hi, i am new in this forum... i am a java programmer trying to do something with c# .net, in this case i am trying to sign multiple pdf files using iTextSharp. This is the code:

public void sign()
{
Org.BouncyCastle.X509.X509CertificateParser cp = new Org.BouncyCastle.X509.X509CertificateParser();
Org.BouncyCastle.X509.X509Certificate[] chain = new Org.BouncyCastle.X509.X509Certificate[] { cp.ReadCertificate(this.getCertificate().RawData) };
bool bHasPrivateKey;
bHasPrivateKey = this.getCertificate().HasPrivateKey;
if (!bHasPrivateKey)
{
MessageBox.Show("El certificado seleccionado no es válido para firmar digitalmente.");
return;
}
PdfReader reader = new PdfReader(this.getOriginalFileName());
FileStream signedFileStream = new FileStream(this.getSignedFileName(), FileMode.Create);
PdfStamper stp = PdfStamper.CreateSignature(reader, signedFileStream, '\0', null, true);
sap = stp.SignatureAppearance;
appearanceHandler.setAppearanceStyleTo(sap, appearanceStyle, new System.Drawing.Rectangle(100, 100, 200, 300));
sap.SetCrypto(null, chain, null, null);
sap.Location = PdfPKCS7.GetSubjectFields(chain[0]).GetField("L");
sap.Contact = this.contactInfo;
sap.Reason = this.getReason();
sap.Acro6Layers = true;
PdfSignature dic = new PdfSignature(PdfName.ADOBE_PPKMS, PdfName.ADBE_PKCS7_SHA1);
dic.Date = new PdfDate(sap.SignDate);
dic.Name = PdfPKCS7.GetSubjectFields(chain[0]).GetField("CN");
if (sap.Reason != null)
dic.Reason = sap.Reason;
if (appearanceHandler.showLocation)
dic.Location = sap.Location;
if (appearanceHandler.showContact)
dic.Contact = sap.Contact;
sap.CryptoDictionary = dic;
int csize = 15000;
Hashtable exc = new Hashtable();
exc[PdfName.CONTENTS] = csize * 2 + 2;
sap.PreClose(exc);
try
{
RSACryptoServiceProvider rsa = (RSACryptoServiceProvider) this.certificate.PrivateKey;
SHA1Managed sha = new SHA1Managed();
byte[] hashedData = sha.ComputeHash(sap.RangeStream);
byte[] sig = rsa.SignHash(hashedData, CryptoConfig.MapNameToOID("SHA1"));
bool verified = rsa.VerifyHash(hashedData, "SHA1", sig);
MessageBox.Show("Verified: " + verified);
byte[] outc = new byte[csize];
PdfDictionary dic2 = new PdfDictionary();
Array.Copy(sig, 0, outc, 0, sig.Length);
dic2.Put(PdfName.CONTENTS, new PdfString(outc).SetHexWriting(true));
sap.Close(dic2);
signedFileStream.Close();
}
catch (CryptographicException ce)
{
MessageBox.Show(ce.Message);
}
}

I iterate the sign method one time for each pdf file.

I use a private CSP instead the Microsoft Base CSP, because i need to do a massive signature of files, when i tried to do that with the Microsoft CSP, the application hangs and throws a Cryptographic Exception, the only way that i found to get it works, was to use the CSP provided by the token manufacturer.

When i used the Microsoft CSP with CMSSigner, everything, except the massive signature, went well... when i signed a single pdf file, the signature was verified correct by adobe reader. But now with this code, using the Safenet CSP,the massive signature work fine but all signatures are verified wrong... the message that acrobat reader throws is: "Error decoding BER:".
I do not know what can i do for solve this. Any Ideas on what could be happen?,

Thanks in advance,

Juan Manuel Diaz

8 Replies

Know the answer? Post it — somebody with the same question will find it here.

Marvin Reid3y ago

A solution you can look into for signing PDFs is by leveraging the PDFFile SignDocument method. Here is a code snippet and a tutorial you can use:

static void SignPDFDocument(string inputPdf, string outputPdf, string signatureFile, string password = null) 
{ 
   try 
   { 
      PDFFile inputDoc = new PDFFile(inputPdf); 
      inputDoc.SignDocument(outputPdf, signatureFile, password); 
   } 
   catch (Exception ex) 
   { 
      Console.WriteLine(ex.Message); 
      return; 
   } 
   Console.WriteLine("Signed PDF successfully"); 
}

https://www.leadtools.com/help/sdk/tutorials/dotnet-fx-console-add-a-digital-signature-to-a-pdf.html

Sapna Girish6y ago
Here is an alternative solution based on Spire.PDF for Java. The following article includes three examples of how to add digital signatures to PDF.

https://dev.to/eiceblue/add-digital-signatures-to-pdf-in-java-31fj
Ram Prakash6y ago
How do sign PDF with Timestamp using USB DSC Token, Please share the code on my email id, [email protected]

Thanks in advance.
Gabrielius Liaškus11y ago
It's been a while from 2009, but have you found the solution? I too try to sign multiple documents with iTextSharp by entering PIN programmatically as an argument, and get asked for pin from the 2nd time to nth. I guess, it might be related.
Xavier Cusi16y ago
Hi Juan Manuel,
I've the same problem, i need to sign a lot of pdf documents and i wan
I have the same problem. I need to sign many pdf documents and pass the pin with a variable, because I have to do it in a batch process.

Have you had any response? You could solve your problem? appreciate any help.

Thank you very much in advance
Xavi Cusí Oliveras.
Juan Manuel Diaz17y ago
any idea? i am still dealing with this issue...

Best Regards!!!,

Juan Manuel
Juan Manuel Diaz17y ago
Oh, my friend, i really want to do that, but i cant. I would brake a code policy of the goverment, for wich i work for. Anyway there is nothing more that i show you, the rest of the code is a form for managing the files and signature styles, this forms iterates the call to method sign, and a class called PDFSignatureAppearanceHandler wich have a method called "setAppearanceStyleTo", wich reads a xml file and apply some styles to the PDFSignatureAppearance object. I hope that this help you to give my an answer. The error is that the signed pdf has invalids signatures, because Acrobat Reader "can not decode Ber"... :(

Best Regards,

Juan Manuel Diaz
Roei Bar17y ago
hey there,

its a bit hard to help cause i cant see the entire picture,

would you like to send me the project to my personal Email

[email protected]

so i can have a look @ it and see the problem, cause the code seems perfectly OK

u