使用 iText 使用 ExternalSiging 服务进行 PDF 签名，

Question

我有一个 pdf 文档，需要进行数字签名，并且签名由外部服务提供。在启动签名之前我没有证书链。我尝试了以下代码，但收到 SigDict/Contents 非法数据消息。

创建文档哈希的源并将其发布到外部服务以对其进行签名

    InputStream data = null;
    DocumentSignStatus documentSignStatus = new DocumentSignStatus();
    int contentEstimated = 8192;

    PdfReader reader = new PdfReader(requestParams.getDocumentToBeSigned());
    try {
    reader.unethicalreading = true;

    int pdfPagenumber = 1;

    if((Integer)requestParams.getSignPageNo() == null || requestParams.getSignPageNo()==0  ){           
        //pdfPagenumber = 1; // Default signature on first page.
        pdfPagenumber = reader.getNumberOfPages(); // Sign on last page

    }else {
        pdfPagenumber = requestParams.getSignPageNo();
    }

    PdfSignatureAppearance appearance = null;
    ByteArrayOutputStream  os = null;

    os = new ByteArrayOutputStream ();
    PdfStamper stamper = PdfStamper.createSignature(reader, os, '\0', null, true);

    Calendar cal = Calendar.getInstance();        
    appearance = stamper.getSignatureAppearance();        
    appearance.setSignDate(cal);
    appearance.setAcro6Layers(false);
    appearance.setReason("Test Signature");
    appearance.setLocation("India");               
    appearance.setImage(null);
    appearance.setCertificationLevel(PdfSignatureAppearance.CERTIFIED_NO_CHANGES_ALLOWED);

    Rectangle rect = requestParams.getRect();        
    appearance.setVisibleSignature(rect, pdfPagenumber, null);

    HashMap<PdfName, Integer> exc = new HashMap<PdfName, Integer>();
    exc.put(PdfName.CONTENTS, new Integer(contentEstimated * 2 + 2));
    PdfSignature dic = new PdfSignature(PdfName.ADOBE_PPKLITE, PdfName.ADBE_PKCS7_DETACHED);
    dic.setReason(appearance.getReason()); 
    dic.setLocation(appearance.getLocation());
    dic.setContact(appearance.getContact());
    dic.setDate(new PdfDate(appearance.getSignDate()));
    appearance.setCryptoDictionary(dic);

    appearance.preClose(exc);

    data = appearance.getRangeStream();    

    MessageDigest messageDigest;
    String provider = null;
    String hashAlgorithm = DigestAlgorithms.SHA256;
    if (provider == null){
        messageDigest = MessageDigest.getInstance(hashAlgorithm);
    }else {
        messageDigest = MessageDigest.getInstance(hashAlgorithm,provider);
    }


    int read = 0;
    byte[] buff = new byte[contentEstimated];

    while ((read = data.read(buff, 0, contentEstimated)) > 0)
    {
        messageDigest.update(buff,0,read);                      
    }
    byte[] hashDigest = messageDigest.digest();

    byte[] documentHash = org.bouncycastle.util.encoders.Hex.encode(hashDigest);

    //eSign Start        
    String hashdocument = new String(documentHash, "UTF-8");        
    System.out.println("Document Hash :"+hashdocument);


    //Generate Sign Request XML for external source to sign the document hash                
    String eSignXmlStr = esignXML.generateEsignXML20(hashdocument,requestParams.getAadhaarNo());                
    String eSignSignedXML = myXMLSigner.signXML(eSignXmlStr, true);
    System.out.print("sign request xml: " + eSignSignedXML);
    // sign request xml generation complete


    documentSignStatus.setSignedXML(eSignSignedXML);        
    session.put("hashdocument", documentHash);
    session.put("appearance", appearance);
    session.put("baos", os);

    }catch(Exception e) {
        e.printStackTrace();
    }
    return documentSignStatus;

以下是将PKCS7响应附加到pdf以完成签名程序并获得签名的pdf的来源。

    byte[] hashdocument = (byte[])session.get("hashdocument");
    PdfSignatureAppearance appearance =  (PdfSignatureAppearance)session.get("appearance");
    ByteArrayOutputStream os = (ByteArrayOutputStream)session.get("baos");

    //Get signed response xml
    InputStream x = request.getInputStream();
    String responseXML = IOUtils.toString(x, "UTF-8");
    System.out.print("REsponse:" + responseXML);

    //parse the xml and get pkcs7 data
    String pkcs7asString = getPKCS7DataFromDigitalSignatureResponse(responseXML);
    byte[] signedDocByte = org.bouncycastle.util.encoders.Base64.decode(pkcs7asString);

    //////////////////// ADD SIGNED BYTES/HASH TO PDF DOCUMENT.                 
    int contentEstimated = 8129;
    byte[] paddedSig = new byte[contentEstimated];                   
    System.arraycopy(signedDocByte, 0, paddedSig, 0, signedDocByte.length);
    PdfDictionary dic2 = new PdfDictionary();
    dic2.put(PdfName.CONTENTS, new PdfString(paddedSig).setHexWriting(true));
    try {
        appearance.close(dic2);
    } catch (DocumentException e) {
        e.printStackTrace();
    }                   
    try(OutputStream outputStream = new FileOutputStream("/SignTest2.0.pdf")) {
        os.writeTo(outputStream);
    }

    os.close();                                             

getPKCS7DataFromDigitalSignatureResponse(responseXML) 方法用于解析外部服务响应，它返回一个 PKCS7 作为字符串。 我试图找出问题所在，但找不到根本原因。 任何人都可以帮助解决这个问题。使用 itext 版本 5.4.5 复制 od 签名文件是 PDF with Signature Problem

Answer 1

我找到了问题的根本原因，我犯了一个小错误，由于 paddedSig 没有正确创建，因此上述源中的内容估计变量不正确。 如上来源所示的错误值。 int contentEstimated = 8129; 正确值为int contentEstimated = 8192; 其余代码没问题。