java - 使用iText(signdeferred)创建PDF数字签名，验证签名时出现invalid signature问题

Question

我是一名中国软件开发人员，我现在正在实现这样一个功能，使用Android客户端对PDF进行数字签名，我的实现是这样的

1. 在服务器上创建一个空白签名
2. 发送带有空白签名的PDF hash到Android客户端，Android客户端对hash进行签名
3. 使用签名。 signdeferred() 合并服务器中的签名内容现在遇到这样一个问题，签名后的PDF不能被PDF阅读器校验。显示PDF文件被篡改，需要注意的是，我使用的是sm3和sm2算法。 Adobe Reader 无法验证它。我们有自己的读者

https://drive.google.com/file/d/127nVvJ0qtSdG53jM0_GUP-WORYrQ5TBo/view?usp=sharing现在我加上PDF文件地址，谁能帮我分析一下问题

 /**
 * @return name.ldd.electSign.webservice.pdf.presign.PresignResponseDetail
 * @Author 焦康
 * @Description 预签章
 * @Date 2021/4/25 14:35
 * @Param [pdfReader, tempFile, temp, chain, positions, fieldName, calendar, hashName]
 **/
public PreSignResponseDetail preSign(PreSignDAO preSignDAO) throws IOException, DocumentException, GeneralSecurityException {
    log.debug("执行预签章");
    FileOutputStream fileOutputStream = new FileOutputStream(preSignDAO.getTempPath());
    // 设置印章信息
    preSignDAO.getPdfReader().setAppendable(true);
    PdfStamper pdfStamper = PdfStamper.createSignature(preSignDAO.getPdfReader(), fileOutputStream, '\0', null, true);
    pdfStamper.getWriter().setCompressionLevel(PdfStream.BEST_COMPRESSION);
    PdfSignatureAppearance pdfSignatureAppearance = pdfStamper.getSignatureAppearance();
    pdfSignatureAppearance.setReason("");
    pdfSignatureAppearance.setLocation("");
    pdfSignatureAppearance.setContact("");
    pdfSignatureAppearance.setLayer2Text("");
    pdfSignatureAppearance.setLayer4Text("");
    pdfSignatureAppearance.setSignatureCreator("");
    pdfSignatureAppearance.setOpacity(preSignDAO.getSealOpacity());
    pdfSignatureAppearance.setCertificationLevel(PdfSignatureAppearance.NOT_CERTIFIED);
    pdfSignatureAppearance.setRenderingMode(PdfSignatureAppearance.RenderingMode.DESCRIPTION);
    pdfSignatureAppearance.setCertificate(preSignDAO.getCertificateChain()[0]);
    pdfSignatureAppearance.setVisibleSignature(new Rectangle(200, 200, 300, 300), preSignDAO.getPage(), preSignDAO.getFieldName());
    // 设置签名图片
    //读取图章图片，这个image是itext包的image
    Image image = Image.getInstance(preSignDAO.getSealImagePath());
    pdfSignatureAppearance.setImage(image);
    // 开始预签章
    ExternalSignatureContainer externalBlankSignatureContainer = new ExternalBlankSignatureContainer(PdfName.ADOBE_PPKLITE, PdfName.ADBE_PKCS7_DETACHED);
    MakeSignature.signExternalContainer(pdfSignatureAppearance, externalBlankSignatureContainer, 8192);
    // 计算hash
    InputStream inputStream = pdfSignatureAppearance.getRangeStream();
    BouncyCastleDigest bouncyCastleDigest = new BouncyCastleDigest();
    byte[] hash = DigestAlgorithms.digest(inputStream, bouncyCastleDigest.getMessageDigest(preSignDAO.getHashAlgorithm()));
    PdfPKCS7 pkcs7 = new PdfPKCS7(null, preSignDAO.getCertificateChain(), preSignDAO.getHashAlgorithm(), null, bouncyCastleDigest, false);
    byte[] sh = pkcs7.getAuthenticatedAttributeBytes(hash, Calendar.getInstance(), null, null, MakeSignature.CryptoStandard.CMS);
    String stringSh = new sun.misc.BASE64Encoder().encode(sh);
    return new PreSignResponseDetail(preSignDAO.getSourcePath(), preSignDAO.getTempPath(), hash, stringSh.replace("\r\n",""), preSignDAO.getFieldName());

}

/**
     * @Author 焦康
     * @Description 数据签名
     * @Date 2021/4/30 14:57
     * @Param [Pin, CN, signData, listener]
     * @return void
     **/
    public void ZAYK_SignData(final String Pin,final String CN,final String signData,HttpsCallbackListener listener){
        httpsCallbackListener = listener;
        new Thread(new Runnable() {
            @Override
            public void run() {
                String result = null;
                try {
                    byte[] bytes = Base64.decode(signData,Base64.DEFAULT);
                    result = service.SDZM_SignData(bytes,CN,Pin);
                    JSONObject jsonObject = JSONObject.parseObject(result);
                    result = jsonObject.getString("signValue");
                    Log.e("SDZM_SignData",result);
                } catch (Exception e) {
                    e.printStackTrace();
                }
                sendMessage(result);
            }
        }).start();
    }

/**
     * @return
     * @Author 焦康
     * @Description 延迟签章
     * @Date 2021/4/25 17:01
     * @Param
     **/
    public DeferredSignResponseDetail DeferredSign(DeferredSignDAO deferredSignDAO) {
        log.debug("执行延迟签章");
        BouncyCastleDigest bouncyCastleDigest = new BouncyCastleDigest();
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(new Date());
        PdfReader pdfReader = null;
        FileOutputStream os = null;
        try {
            PdfPKCS7 sgn = new PdfPKCS7(null, deferredSignDAO.getCertificateChain(), deferredSignDAO.getHashAlgorithm(), null, bouncyCastleDigest, false);
            sgn.setExternalDigest(deferredSignDAO.getSignData(), null, deferredSignDAO.getDigestEncryptionAlgorithm());
            byte[] sig = sgn.getEncodedPKCS7(deferredSignDAO.getHashData(), calendar, null, null, null, MakeSignature.CryptoStandard.CMS);
            pdfReader = new PdfReader(deferredSignDAO.getTempPath());
            os = new FileOutputStream("D:\\ruoyi\\uploadPath\\pdf\\Dest\\输出");
            ExternalSignatureContainer external = new MyExternalSignatureContainer(sig);
            MakeSignature.signDeferred(pdfReader, deferredSignDAO.getFieldName(), os, external);
        } catch (Exception e) {
            log.error("延迟签章出错:", e);
        } finally {
            if (pdfReader != null) {
                pdfReader.close();
            }
            try {
                if (os != null) {
                    os.close();
                }
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        }
        return new DeferredSignResponseDetail(deferredSignDAO.getTargetPath() + ".pdf");
    }

public class MyExternalSignatureContainer implements ExternalSignatureContainer {
    byte[] sig = null;
    
    public MyExternalSignatureContainer(byte[] sig) {
        this.sig = sig;
    }

    @Override
    public byte[] sign(InputStream paramInputStream) throws GeneralSecurityException {
        return this.sig;
    }

    @Override
    public void modifySigningDictionary(PdfDictionary paramPdfDictionary) {
    }
}

Answer 1

在计算待签名属性的哈希时，使用当前时间作为签名时间属性的值:

PdfPKCS7 pkcs7 = new PdfPKCS7(null, preSignDAO.getCertificateChain(), preSignDAO.getHashAlgorithm(), null, bouncyCastleDigest, false);
byte[] sh = pkcs7.getAuthenticatedAttributeBytes(hash, Calendar.getInstance(), null, null, MakeSignature.CryptoStandard.CMS);
String stringSh = new sun.misc.BASE64Encoder().encode(sh);

稍后，当您收到该散列的裸签名时，您将使用当时的当前时间重新构建已签名的属性:

Calendar calendar = Calendar.getInstance();
calendar.setTime(new Date());
...
PdfPKCS7 sgn = new PdfPKCS7(null, deferredSignDAO.getCertificateChain(), deferredSignDAO.getHashAlgorithm(), null, bouncyCastleDigest, false);
sgn.setExternalDigest(deferredSignDAO.getSignData(), null, deferredSignDAO.getDigestEncryptionAlgorithm());
byte[] sig = sgn.getEncodedPKCS7(deferredSignDAO.getHashData(), calendar, null, null, null, MakeSignature.CryptoStandard.CMS);

因此，最终 CMS 容器的签名属性中的签名时间与用于散列的签名时间不同，因此签名签署了错误的散列。

要解决此问题，在两个地方使用相同的签名时间值!

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顺便说一句，如果您使用的是当前的 iText 5 版本，您就不会遇到这个问题:因为签名时间属性是可选的(只要在签名字典中设置签名时间)甚至禁止PAdES 签名，当前的 iText 5 版本不再设置该属性，getAuthenticatedAttributeBytes 和 getEncodedPKCS7 不再有 Calendar 参数...

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由于我还没有处理中文算法，所以我无法判断它们是否正确应用在您的代码或示例文件中。

但有一个警告:PdfPKCS7 已在考虑 DSA 和 RSA 的情况下实现；稍后添加了 X9.62 ECDSA 支持，并且有一个错误(iText 7 中仍然存在)，Adobe Acrobat 会忽略但不一定会忽略其他 validator ；因此，在将 PdfPKCS7 用于任何其他算法之前，您必须验证该类是否正确处理了那些其他算法，如果没有，则改进该类。