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java - PDFBox 2.0.15 的外部签名

问题描述

我正在实现一个应用程序来签署服务器中的 PDF 文件，具有以下场景（为了使历史悠久，简短）：

  1. 客户端开始向服务器发送签名、日期/时间和水印
  2. 服务器将签名字典添加到文件中并发送要签名的数据
  3. 客户签到内容
  4. 服务器完成签名

我正在使用 PDFBox 2.0.15，并使用saveIncrementalForExternalSigning如下代码所示的新功能：

try {
        String name = document.getID();
        File signedFile = new File(workingDir.getAbsolutePath() + sep + name + "_Signed.pdf");
        this.log("[SIGNATURE] Creating signed version of the document");
        if (signedFile.exists()) {
            signedFile.delete();
        }
        FileOutputStream tbsFos = new FileOutputStream(signedFile);
        ExternalSigningSupport externalSigning = pdfdoc.saveIncrementalForExternalSigning(tbsFos);

        byte[] content = readExternalSignatureContent(externalSigning);
        if (postparams.get("action").equalsIgnoreCase("calc_hash")) {
            this.log("[SIGNATURE] Calculating hash of the document");
            String strBase64 = ParametersHandle.compressParamBase64(content);

            // this saves the file with a 0 signature
            externalSigning.setSignature(new byte[0]);

            // remember the offset (add 1 because of "<")
            int offset = signature.getByteRange()[1] + 1;

            this.log("[SIGNATURE] Sending calculated hash to APP");
            return new String[] { strBase64, processID, String.valueOf(offset) };
        } else {
            this.log("[SIGNATURE] Signature received from APP");
            String signature64 = postparams.get("sign_disgest");
            byte[] cmsSignature = ParametersHandle.decompressParamFromBase64(signature64);

            this.log("[SIGNATURE] Setting signature to document");
            externalSigning.setSignature(cmsSignature);

            pdfdoc.close();

            IOUtils.closeQuietly(signatureOptions);

            this.log("[DOXIS] Creating new version of document on Doxis");
            createNewVersionOfDocument(doxisServer, documentServer, doxisSession, document, signedFile);

            return new String[] { "SIGNOK" };
        }
    } catch (IOException ex) {
        this.log("[SAVE FOR SIGN] " + ex);
        return null;
    }

在“IF”语句中，我正在生成要签名的数据。在“ELSE”语句中，将通过发布请求（就是这样ParametersHandle.decompressParamFromBase64做的）来的签名添加到文档中。所以我在这次尝试中有两个关于这个方法的帖子请求。

第二种方法是在一个方法中执行每个发布请求，所以我有第二个代码块：

// remember the offset (add 1 because of "<") 
        int offset = Integer.valueOf(postparams.get("offset"));
        this.log("[PDF BOX] Retrieving offset of bytes range for this signature. The value is: "
                + String.valueOf(offset));

        File signedPDF = new File(workingDir.getAbsolutePath() + sep + name + "_Signed.pdf");
        this.log("[SIGNATURE] Reloading document for apply signature: " + signedPDF.getAbsolutePath());

        // invoke external signature service
        String signature64 = postparams.get("sign_disgest");
        byte[] cmsSignature = ParametersHandle.decompressParamFromBase64(signature64);

        this.log("[SIGNATURE] Got signature byte array from APP.");
        // set signature bytes received from the service

        // now write the signature at the correct offset without any PDFBox methods
        this.log("[SIGNATURE] Writing signed document...");
        RandomAccessFile raf = new RandomAccessFile(signedPDF, "rw");
        raf.seek(offset);
        raf.write(Hex.getBytes(cmsSignature));
        raf.close();
        this.log("[SIGNATURE] New signed document has been saved!");

问题是：在 Adob​​e Reader 上验证文档时，我收到错误消息“自应用签名以来文档已被更改或损坏”。据我了解，它不应该发生，因为签名字节范围的偏移量在第二次调用后被记住。

任何帮助或想法表示赞赏，

先感谢您。

[编辑]

有关已使用文件的完整列表：https ://drive.google.com/drive/folders/1S9a88lCGaQYujlEyCrhyzqvmWB-68LR3

[编辑 2]

根据@mkl 评论，这里是签名的方法：

public byte[] sign(byte[] hash)
        throws IOException, NoSuchAlgorithmException, InvalidKeyException, SignatureException {
    PrivateKey privKey = (PrivateKey) windowsCertRep.getPrivateKey(this.selected_alias, "");
    X509Certificate[] certificateChain = windowsCertRep.getCertificateChain(this.selected_alias);

    try
    {
        CMSSignedDataGenerator gen = new CMSSignedDataGenerator();
        X509Certificate cert = (X509Certificate) certificateChain[0];
        ContentSigner sha1Signer = new JcaContentSignerBuilder("SHA256WithRSA").build(privKey);
        gen.addSignerInfoGenerator(new JcaSignerInfoGeneratorBuilder(new JcaDigestCalculatorProviderBuilder().build()).build(sha1Signer, cert));
        gen.addCertificates(new JcaCertStore(Arrays.asList(certificateChain)));
        CMSProcessableInputStream msg = new CMSProcessableInputStream(new ByteArrayInputStream(hash));
        CMSSignedData signedData = gen.generate(msg, false);
        return signedData.getEncoded();
    }
    catch (GeneralSecurityException e)
    {
        throw new IOException(e);
    }
    catch (CMSException e)
    {
        throw new IOException(e);
    }
    catch (OperatorCreationException e)
    {
        throw new IOException(e);
    }

}

我已经测试了这个CreateVisibleSignature2例子，替换了sign调用这个服务的方法，它返回了我的签名，它可以工作。

标签： javapdfdigital-signaturepdfbox

解决方案

感谢Tilman Hausherr，我可以弄清楚发生了什么：

1 - 我有一个与SmatCards等通信的桌面APP，它是签名者。为了与服务器通信（通过网页），我们使用 WebSocket。我编写了自己的 websocket 服务器类，这就是为什么它只准备使用 65k 字节。比我尝试在这里发送数据时：

ExternalSigningSupport externalSigning = doc.saveIncrementalForExternalSigning(fos);           
byte[] cmsSignature = sign(externalSigning.getContent());

我在APP中遇到错误。

2 - Tilman，建议我看看这个@mkl 答案，他在哪里做同样的事情：创建一个 SHA256 哈希externalSigning.getContent()并发送到另一个地方签名。我不知道为什么，但唯一对我不起作用的是：

gen.addSignerInfoGenerator(builder.build(
                new BcRSAContentSignerBuilder(sha256withRSA,
                        new DefaultDigestAlgorithmIdentifierFinder().find(sha256withRSA))
                                .build(PrivateKeyFactory.createKey(pk.getEncoded())),
                new JcaX509CertificateHolder(cert)));

因此，我已将此块替换为：

ContentSigner sha256Signer = new JcaContentSignerBuilder("SHA256WithRSA").build(privKey);

比，我完整的签名方法是这样的：

        PrivateKey privKey = (PrivateKey) windowsCertRep.getPrivateKey(this.selected_alias, "changeit");
    X509Certificate[] certificateChain = windowsCertRep.getCertificateChain(this.selected_alias);

        List<X509Certificate> certList = Arrays.asList(certificateChain);
        JcaCertStore certs = new JcaCertStore(certList);

        CMSSignedDataGenerator gen = new CMSSignedDataGenerator();

        Attribute attr = new Attribute(CMSAttributes.messageDigest,
                new DERSet(new DEROctetString(hash)));

        ASN1EncodableVector v = new ASN1EncodableVector();
        v.add(attr);

        SignerInfoGeneratorBuilder builder = new SignerInfoGeneratorBuilder(new BcDigestCalculatorProvider())
                .setSignedAttributeGenerator(new DefaultSignedAttributeTableGenerator(new AttributeTable(v)));

        AlgorithmIdentifier sha256withRSA = new DefaultSignatureAlgorithmIdentifierFinder().find("SHA256withRSA");

        CertificateFactory certFactory = CertificateFactory.getInstance("X.509");
        InputStream in = new ByteArrayInputStream(certificateChain[0].getEncoded());
        X509Certificate cert = (X509Certificate) certFactory.generateCertificate(in);

        ContentSigner sha256Signer = new JcaContentSignerBuilder("SHA256WithRSA").build(privKey);
        gen.addSignerInfoGenerator(builder.build(sha256Signer, new JcaX509CertificateHolder(cert)));

        gen.addCertificates(certs);

        CMSSignedData s = gen.generate(new CMSAbsentContent(), false);
        return s.getEncoded();

所以，再次感谢社区！

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