使用 PDFBox 2.0.15 的外部签名

Question

我正在实施一个应用程序来在服务器中签署 PDF 文件，具有以下场景（长历史，短历史）：

客户端开始向服务器发送签名，date/time和水印
服务器添加签名字典到文件中并发送待签名数据
客户签到内容
服务器完成签名

我正在使用 PDFBox 2.0.15，并使用新功能 saveIncrementalForExternalSigning，如下面的代码所示：

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，通过 post 请求（ParametersHandle.decompressParamFromBase64 所做的）将签名添加到文档中。所以我在这次尝试中有两个 post 请求此方法。

第二种方法是用一种方法处理每个 post 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：我在 Adobe Reader 上验证时收到错误 "The document has been altered or corrupted since the Signature was applied"。根据我的理解，这不应该发生，因为在第二次 post 调用时会记住签名字节范围的偏移量。

感谢任何帮助或想法，

提前致谢。

[编辑]

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

[编辑 2]

根据@mkl 的评论，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 CreateVisibleSignature2 示例，替换了调用此服务的 sign 方法 returns 我的签名，它有效。

Answer 1

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。我们使用 WebSocket 与服务器通信（通过网页）。我已经编写了自己的 websocket 服务器 class，这就是它只准备使用 65k 字节的原因。比起我尝试在此处发送数据时：

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

我在应用程序中遇到错误。

2 - Tilman 建议我看一下这个，他做了同样的事情：创建 externalSigning.getContent() 的 SHA256 散列并发送到另一个地方进行签名。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);

那么，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！！！

使用 PDFBox 2.0.15 的外部签名

External Signature with PDFBox 2.0.15

java

pdf

digital-signature

pdfbox