External signatures

[joaofortunato91present]

Hello! I am trying to make a digital signature on PDFs and ive been doing some tests with pdfbox-android. First ive tryed to add a external signature on desktop environment with success using the :

ExternalSigningSupport externalSigning = document.saveIncrementalForExternalSigning(fos); byte[] cmsSignature = Files.readAllBytes(pathToSignedHash); externalSigning.setSignature(cmsSignature);

So this is where the problem comes now, i dont have the required classes on the android pdfbox and i cant seem to find a way around it. Any way to make an external signature work in this actual version of android pdfbox or in any soon release?

By the way great work so far :)

[TomRoush]

This class was introduced in v2.0.3 and this library is currently up to date with v1.8.9, so it will be some time before this library will be caught up. I haven't had a chance to take a look at the code for ExternalSigningSupport yet, but I"ll see what it does and if it can easily be replicated easily.

[TomRoush]

I believe I've added the functionality you need if that's the only part that's giving you trouble. I've attached an aar with the necessary changes. pdfbox-android-1.8.9.1.aar.zip

[joaofortunato91present]

Hello Tom! First of all , thanks for the quick response ! I´ve tryed the .aar you uploaded but i have a problem with the implementation. It seems that the methods saveIncrementalForExternalSigning(OutputStream output) and addSignature(PDSignature sigObject) from the PDDocument class do not exist to complete an external signature successfully.

[TomRoush]

I must have missed PDDocument, Try this one. pdfbox-android-1.8.9.1.aar.zip

[joaofortunato91present]

Hey Tom, I´ve been around the code for a while and i keep getting an java.lang.ArrayIndexOutOfBoundsException on the COSWriter.doWriteSignature method that the saveIncrementalForExternalSigning(fos) uses. I´ve tryed many things and i think i have nothing wrong with my code.

The code sample i am using is the following:

`package com.example.joao.pdfboxtests2;

import android.os.Environment; import android.support.v7.app.AppCompatActivity; import android.os.Bundle;

import com.tom_roush.pdfbox.pdmodel.PDDocument; import com.tom_roush.pdfbox.pdmodel.interactive.digitalsignature.ExternalSigningSupport; import com.tom_roush.pdfbox.pdmodel.interactive.digitalsignature.PDSignature;

import java.io.BufferedInputStream; import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.util.Calendar;

public class MainActivity extends AppCompatActivity { final String signedHashLoc = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS) + "/hashSignature-2.sign"; final String pdfToSignLoc = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS) + "/pdftosign.pdf"; final String pdfSignedLoc = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS) + "/pdfsignedAndroid.pdf"; //PDDocument document; FileInputStream docToSignIS, signedHashIS; FileOutputStream docSignedOS; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main);

    try {
        docToSignIS =new FileInputStream(pdfToSignLoc);
        signedHashIS =new FileInputStream(signedHashLoc);
        docSignedOS =new FileOutputStream(pdfSignedLoc);
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }

    //criar o signature dictionary
    PDSignature signature = new PDSignature();
    signature.setFilter(PDSignature.FILTER_ADOBE_PPKLITE);
    signature.setSubFilter(PDSignature.SUBFILTER_ADBE_PKCS7_DETACHED);
    signature.setName("Example User");
    signature.setLocation("Los Angeles, CA");
    signature.setReason("Testing");
    //data da assinatura
    signature.setSignDate(Calendar.getInstance());
    System.out.println("Sign externally...");
    try {
        PDDocument document = PDDocument.load(docToSignIS);
        document.addSignature(signature);
        ExternalSigningSupport externalSigning =document.saveIncrementalForExternalSigning(docSignedOS);
        externalSigning.setSignature(getSignedDigest());
        document.save(docSignedOS);
        document.close();
        docSignedOS.close();
        docToSignIS.close();
        signedHashIS.close();
    } catch (IOException e) {
        e.printStackTrace();
    }

}
public byte[] getSignedDigest(){
    File file = new File(signedHashLoc);
    int size = (int) file.length();
    byte[] bytes = new byte[size];
    try {
        BufferedInputStream buf = new BufferedInputStream(signedHashIS);
        buf.read(bytes, 0, bytes.length);
        buf.close();
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    return bytes;
}

}`

The error it gives is the following: In the line: this.incrementPart[(int)(this.byteRangeOffset + (long)dataToSign - inLength)] = byteRangeBytes[dataToSign];

Meanwhile i´ve tryed to use the following code provided in the samples setup() and happens exactly the same, the arrayIndexOutOfBounds. // Enable Android-style asset loading (highly recommended) PDFBoxResourceLoader.init(getApplicationContext()); // Find the root of the external storage. root = android.os.Environment.getExternalStorageDirectory(); assetManager = getAssets(); PDDocument document = PDDocument.load(assetManager.open("pdftosign.pdf")); Thanks in advance

[crockercaria]

I too get the same error 👍

.. java.lang.RuntimeException: ... Caused by: java.lang.ArrayIndexOutOfBoundsException: length=20732; index=767721 at com.tom_roush.pdfbox.pdfwriter.COSWriter.doWriteSignature(COSWriter.java:722)
at com.tom_roush.pdfbox.pdfwriter.COSWriter.visitFromDocument(COSWriter.java:1114)

public ExternalSigningSupport saveIncrementalForExternalSigning(OutputStream output) throws IOException { if(this.pdfSource == null) { throw new IllegalStateException("document was not loaded from a file or a stream"); } else { COSWriter writer = new COSWriter(output, this.pdfSource); writer.write(this); ***** this.signingSupport = new SigningSupport(writer); return this.signingSupport; } }

The error is here ** in the write(this)

public void write(PDDocument doc) throws IOException { this.write(doc, (SignatureInterface)null); } is the null correct ?

[TomRoush]

Seems like this is more difficult than I hoped. Would it be possible for either of you to share a test signature file that fails that I could use for testing?

[joaofortunato91present]

Hey Tom, Can i have an email to send you the files im using for testing? Some of them are kind of private :)

[TomRoush]

Never mind, I managed to get the error again with my signature.

[joaofortunato91present]

Hello Tom, I have been analyzing the error and i believe i have found the solution by comparing code between the original PDFBox (https://github.com/apache/pdfbox/tree/2bf48eed0223118c22b19c53cff20a2c5ba5fb95) and PDFBox-Android, since i had an external signature solution working on the original one. By comparing what was added to the original one i have found that by switching the code long inLength = incrementalInput.available(); for long inLength = incrementalInput.length(); at the COSWriter.java class it seems to work fine.

[TomRoush]

That's great. I can't check right now, but if everything works as it should, feel free to make a pull request.

[mohitatray]

Sorry if this is a nub question but I do not find ExternalSigningSupport class when I add this line in build.gradle dependencies - implementation 'com.tom_roush:pdfbox-android:1.8.10.1'

This class is not available - import com.tom_roush.pdfbox.pdmodel.interactive.digitalsignature.ExternalSigningSupport;

Why? Does this library still depends on PDFBox below v2.0.3? And can you tell me how to follow these steps to sign PDF using pdfbox-android? I only need this library to digitally sign PDFs. I can generate PDF by PdfDocument class in android.