java - 使用现有证书、中间文件和远程创建的签名，使用 itextpdf for Java 对 PDF 进行两步签名

Question

用例如下:本地应用程序必须使用远程服务器上生成的完整PKCS#7分离签名来签署 PDF 文档，该签名需要由 e 发送的一次性密码-邮件/短信；远程服务器根据关联的文档哈希生成分离签名，生成的签名是“外部签名”签名”，如 CMS RFC (RFC5652) 第 5.2 节中所定义，例如生成的签名文件是一个单独的文件。

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我花了好几天的时间来为这个用例实现一个可行的解决方案(使用itextpdf 5.5.13.1)，但最终签名的文件的签名错误，并显示消息“认证” by 无效”——请参阅附加的“signed_with_error”文件。概念性的“两步签名”实现流程是:

第一步:从原始文档文件 - 请参阅“原始”附加文件 - 我创建一个中间文件 - 请参阅附加的“中间”文件 - 我在其中创建了插入一个空签名，根据该签名创建关联的文档哈希。本步骤保存签名摘要，以供下一步使用

第二步:调用远程服务器，接收分离的签名文件，并且我通过使用之前的签名摘要将预签名文件中的内容插入到签名中来创建签名文件从远程服务器接收到的步骤和分离的签名内容。

原始、中间和带有错误的签名示例文件是:
original
intermediary
signed_with_error

有人知道我下面的代码可能有什么问题吗？
相关代码部分如下:

第一步:

        ByteArrayOutputStream preSignedDocument = new ByteArrayOutputStream();
        Path customerPathInDataStorage = storageService.resolveCustomerPathInDataStorage(customerExternalId);
        PdfReader pdfReader = new PdfReader(originalDocumentContent);
        PdfStamper stamper = PdfStamper.createSignature(pdfReader, preSignedDocument, '\0', customerPathInDataStorage.toFile(), true);

        // create certificate chain using certificate received from remote server system
        byte[] certificateContent = certificateInfo.getData(); // this is the customer certificate received one time from the remote server and used for every document signing initialization
        X509Certificate certificate = SigningUtils.buildCertificateFromCertificateContent(certificateContent);
        java.security.cert.Certificate[] certificatesChain = CertificateFactory.getInstance(CERTIFICATE_TYPE).generateCertPath(
                Collections.singletonList(certificate)).getCertificates().toArray(new java.security.cert.Certificate[0]);

        // create empty digital signature inside pre-signed document
        PdfSignatureAppearance signatureAppearance = stamper.getSignatureAppearance();
        signatureAppearance.setVisibleSignature(new Rectangle(72, 750, 400, 770), 1, "Signature_" + customerExternalId);
        signatureAppearance.setCertificationLevel(PdfSignatureAppearance.CERTIFIED_NO_CHANGES_ALLOWED);
        signatureAppearance.setCertificate(certificate);
        CustomPreSignExternalSignature externalSignatureContainer =
                new CustomPreSignExternalSignature(PdfName.ADOBE_PPKLITE, PdfName.ADBE_PKCS7_DETACHED);
        MakeSignature.signExternalContainer(signatureAppearance, externalSignatureContainer, 8192);

        ExternalDigest digest = new SignExternalDigest();
        PdfPKCS7 pdfPKCS7 = new PdfPKCS7(null, certificatesChain, DOCUMENT_HASHING_ALGORITHM, null, digest, false);
        byte[] signatureDigest = externalSignatureContainer.getSignatureDigest();
        byte[] authAttributes = pdfPKCS7.getAuthenticatedAttributeBytes(signatureDigest, null, null,
                MakeSignature.CryptoStandard.CMS);

        pdfReader.close();

        documentDetails.setPreSignedContent(preSignedDocument.toByteArray()); // this is the intermediary document content used in 2nd step in the line with the comment ***PRESIGNED_CONTENT****
        documentDetails.setSignatureDigest(signatureDigest); // this is the signature digest used in 2nd step in the line with comment ****SIGNATURE_DIGEST****
        byte[] hashForSigning = DigestAlgorithms.digest(new ByteArrayInputStream(authAttributes),
                digest.getMessageDigest(DOCUMENT_HASHING_ALGORITHM));
        documentDetails.setSigningHash(hashForSigning); // this is the hash sent to remote server for signing

第二步:

        // create certificate chain from detached signature
        byte[] detachedSignatureContent = documentDetachedSignature.getSignature(); // this is the detached signature file content received from the remote server which contains also customer the certificate
        X509Certificate certificate = SigningUtils.extractCertificateFromDetachedSignatureContent(detachedSignatureContent);
        java.security.cert.Certificate[] certificatesChain = CertificateFactory.getInstance(CERTIFICATE_TYPE).generateCertPath(
                    Collections.singletonList(certificate)).getCertificates().toArray(new java.security.cert.Certificate[0]);

        // create digital signature from detached signature
        ExternalDigest digest = new SignExternalDigest();
        PdfPKCS7 pdfPKCS7 = new PdfPKCS7(null, certificatesChain, DOCUMENT_HASHING_ALGORITHM, null, digest, false);

        pdfPKCS7.setExternalDigest(detachedSignatureContent, null, SIGNATURE_ENCRYPTION_ALGORITHM);
        byte[] signatureDigest = documentVersion.getSignatureDigest(); // this is the value from 1st step for ****SIGNATURE_DIGEST****
        byte[] encodedSignature = pdfPKCS7.getEncodedPKCS7(signatureDigest, null, null, null, MakeSignature.CryptoStandard.CMS);
        ExternalSignatureContainer externalSignatureContainer = new CustomExternalSignature(encodedSignature);

        // add signature content to existing signature container of the intermediary PDF document
        PdfReader pdfReader = new PdfReader(preSignedDocumentContent);// this is the value from 1st step for ***PRESIGNED_CONTENT****
        ByteArrayOutputStream signedPdfOutput = new ByteArrayOutputStream();
        MakeSignature.signDeferred(pdfReader, "Signature_" + customerExternalId, signedPdfOutput, externalSignatureContainer);

        return signedPdfOutput.toByteArray();

依赖关系:

public static final String DOCUMENT_HASHING_ALGORITHM = "SHA256";
public static final String CERTIFICATE_TYPE = "X.509";
public static final String SIGNATURE_ENCRYPTION_ALGORITHM = "RSA";

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public class CustomPreSignExternalSignature implements ExternalSignatureContainer {

    private static final Logger logger = LoggerFactory.getLogger(CustomPreSignExternalSignature.class);

    private PdfDictionary dictionary;
    private byte[] signatureDigest;

    public CustomPreSignExternalSignature(PdfName filter, PdfName subFilter) {
        dictionary = new PdfDictionary();
        dictionary.put(PdfName.FILTER, filter);
        dictionary.put(PdfName.SUBFILTER, subFilter);
    }

    @Override
    public byte[] sign(InputStream data) throws GeneralSecurityException {
        try {
            ExternalDigest digest = new SignExternalDigest();
            signatureDigest = DigestAlgorithms.digest(data, digest.getMessageDigest(DOCUMENT_HASHING_ALGORITHM));
        } catch (IOException e) {
            logger.error("CustomSignExternalSignature - can not create hash to be signed", e);
            throw new GeneralSecurityException("CustomPreSignExternalSignature - can not create hash to be signed", e);
        }

        return new byte[0];
    }

    @Override
    public void modifySigningDictionary(PdfDictionary pdfDictionary) {
        pdfDictionary.putAll(dictionary);
    }

    public byte[] getSignatureDigest() {
        return signatureDigest;
    }
}

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public class CustomExternalSignature implements ExternalSignatureContainer {

        private byte[] signatureContent;

        public CustomExternalSignature(byte[] signatureContent) {
            this.signatureContent = signatureContent;
        }

        @Override
        public byte[] sign(InputStream data) throws GeneralSecurityException {
            return signatureContent;
        }

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

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public class SignExternalDigest implements ExternalDigest {

    @Override
    public MessageDigest getMessageDigest(String hashAlgorithm) throws GeneralSecurityException {
        return DigestAlgorithms.getMessageDigest(hashAlgorithm.toUpperCase(), null);
    }

}

稍后评论:

即使它不正确，我也观察到，如果在第二步中，而不是行:

byte[] signatureDigest = documentVersion.getSignatureDigest(); // this is the value from 1st step for ****SIGNATURE_DIGEST****

我将使用:

byte[] signatureDigest = new byte[0];

将生成带有可见证书的签名文件，该证书可以验证，但 PDF 文档无效，并出现错误“文档认证无效”。 ---“自申请认证以来，该文件已被更改或损坏。” - 请参阅附件signed_certification_invalid 。它看起来合法无效，但对我来说很奇怪，为什么在这种情况下认证显示在文档中，但在使用我认为的“正确的”signatureDigest 值时它被破坏了。

Answer 1

你说

the remote server generates the detached signature based on the associated document hash and the resulting signature is an “external signature”, as defined in the CMS RFC (RFC5652), section 5.2

因此，您在步骤 2 中检索到的内容:

// create certificate chain from detached signature
byte[] detachedSignatureContent = documentDetachedSignature.getSignature(); // this is the detached signature file content received from the remote server which contains also customer the certificate

已经是 CMS 签名容器。因此，您不能再像在以下几行中那样将其插入 PKCS#7/CMS 签名容器中，但可以立即将其插入 PDF 中。

所以你的第二步应该是

// create certificate chain from detached signature
byte[] detachedSignatureContent = documentDetachedSignature.getSignature(); // this is the detached signature file content received from the remote server which contains also customer the certificate
ExternalSignatureContainer externalSignatureContainer = new CustomExternalSignature(detachedSignatureContent);

// add signature content to existing signature container of the intermediary PDF document
PdfReader pdfReader = new PdfReader(preSignedDocumentContent);// this is the value from 1st step for ***PRESIGNED_CONTENT****
ByteArrayOutputStream signedPdfOutput = new ByteArrayOutputStream();
MakeSignature.signDeferred(pdfReader, "Signature_" + customerExternalId, signedPdfOutput, externalSignatureContainer);

return signedPdfOutput.toByteArray();

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此外，还会签署错误的哈希值。事实上，在第 1 步中，您也不应该使用 PdfPKCS7 类，而只需使用

documentDetails.setSigningHash(externalSignatureContainer.getSignatureDigest()); // this is the hash sent to remote server for signing