java iText7延迟符号前缀产生无效的签名pdf

Question

使用iText7，我试图对PDF进行签名，以获得外部实体的签名。该过程必须按如下方式执行

• 使用Web服务并获得证书，
• 获取要签名的PDF哈希。哈希在发送到外部实体进行签名之前必须有前缀。
• 我为此创建了一个临时PDF。
• 在信息交换中使用网络服务。
• 发送哈希；
• 通过短信获取确认；
• 获取签名的哈希。
• 使用签名的哈希，我签署最终的PDF。

问题是，我发现一个错误，即在应用签名后，文档已被更改或损坏<项目实施是。

private final String _pdfToBeSigned = "C:/tmp/ama/PDF1.pdf";
private final String _temporaryPdf = "C:/tmp/ama/PDF1_empty.pdf";
private final String _finalPdf = "C:/tmp/ama/PDF1_assinado.pdf";

private final String _signatureFieldname = "sign1";

private static X509Certificate[] _chain = null;
private static Collection<byte[]> _crlBytesList = null;
private static Collection<byte[]> _ocspBytesList = null;

public static void main(String[] a) throws GeneralSecurityException, IOException {
    //Certificates (3) of the service are obtained. 
    _chain = getCertificates();
    
    TSAClientBouncyCastle tsaClient = new TSAClientBouncyCastle("https://freetsa.org/tsr");
    CrlClientOnline crlClients = new CrlClientOnline(_chain);
    OcspClientBouncyCastle ocspClient = new OcspClientBouncyCastle(null);
    
    _crlBytesList = getCrlByteList(crlClients);
    _ocspBytesList = getOcspBytesList(ocspClient);
    
    TestSign test = new TesteSign();        
    
    List<byte[]> hashs = test.getPreSignPDF(tsaClient, ocspClient);
    
    //Note: send hash to sign and wait for return of SMS with code
    //      if SMS code ok, the signed hash is obtained. 
    byte[] hashSignedForAma = getHashSignedByAma(hashs.get(0));
    
    //Finally sign the PDF 
    test.setFinalSignPDF(hashSignedForAma, hashs.get(1), tsaClient);
}

private static Collection<byte[]> getCrlByteList(CrlClientOnline crlClients){
     if(crlClients == null) return null;
     Collection<byte[]> coll = null;
     for(int i=0;i<_chain.length;i++) {
         Collection<byte[]> tmp = crlClients.getEncoded(_chain[i], null);
         if(null != tmp ) {
             coll = new ArrayList<byte[]>();
             coll.addAll(tmp);
         }
     }
     return coll;
}
      
private static Collection<byte[]> getOcspBytesList(OcspClientBouncyCastle ocspClient) {
   if(_chain.length <= 1 ||
      ocspClient == null) {
       return null;
   }
   Collection<byte[]> list = new ArrayList<byte[]>();
   for(var i = 0; i < _chain.length - 1; i++) {
       byte[] encoded = ocspClient.getEncoded(_chain[i], _chain[i + 1], null);
       if(encoded != null) {
           list.add(encoded);
       }
   }
   return list;

}

获取PDF哈希进行签名。散列必须在发送给外部实体进行签名之前具有前缀，并为此创建临时PDF。

public List<byte[]> getPreSignPDF(TSAClientBouncyCastle tsaClient_, OcspClientBouncyCastle ocspClient_) throws GeneralSecurityException, IOException {
    try (OutputStream ops = new FileOutputStream(_temporaryPdf);){
        PdfReader reader = new PdfReader(_pdfToBeSigned);
        StampingProperties prop = new StampingProperties();

        PdfSigner pdfSigner = new PdfSigner(reader, ops, prop);

        pdfSigner.setFieldName(_signatureFieldname);

        PdfSignatureAppearance  appearance = pdfSigner.getSignatureAppearance();

        appearance.setPageRect(new Rectangle(10,750,150,50))
                  .setPageNumber(1)
                  .setLayer2FontSize(6f)
                  .setReason("reason")
                  .setLocation("location")                    
                  .setCertificate(_chain[0]);

        Prepare4AmaSigningContainer container = new Prepare4AmaSigningContainer();
        
        //calculate estimed size
        int estimatedSize = 8192 + //initial base container size
                ( ocspClient_ != null ? 4192 : 0 ) +
                ( tsaClient_ != null  ? 4600 : 0 );
        if(_crlBytesList != null) {
            for (byte[] bs : _crlBytesList) {
                estimatedSize+= bs.length + 10;
            }
        }
        pdfSigner.signExternalContainer(container, estimatedSize); 

        byte[] HashForSigning = container.getHashToBeSignedByAma();
        byte[] NakeHash = container.getHashToBeSignedByAma();
        
        List<byte[]> array = new ArrayList<byte[]>();
        array.add(HashForSigning);  //idx 0
        array.add(NakeHash);        //idx 1
        
        return array;           
    }
}

//***** CLASS ****
class Prepare4AmaSigningContainer extends ExternalBlankSignatureContainer{

    private final byte[] _sha256SigPrefix = {0x30, 0x31, 0x30, 0x0d, 0x06, 0x09, 0x60, (byte)0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, 0x05, 0x00, 0x04, 0x20};
    private byte[] hashToBeSignedByAma;
    private byte[] nakeHash = null; 
    
    public Prepare4AmaSigningContainer(){
        super(PdfName.Adobe_PPKLite, PdfName.Adbe_pkcs7_detached);
    }

    public byte[] getHashToBeSignedByAma() {
        return hashToBeSignedByAma;
    }
    
    public byte[] getNakeHash() {
        return nakeHash;
    }
    
    @Override
    public byte[] sign(InputStream data){
        try {
            // create pdf pkcs7 for signing the document
            BouncyCastleDigest digest = new BouncyCastleDigest();
            PdfPKCS7 sgn = new PdfPKCS7(null, _chain, DigestAlgorithms.SHA256, null, digest, false);
            
            // get hash for document bytes
            nakeHash = DigestAlgorithms.digest(data, digest.getMessageDigest(DigestAlgorithms.SHA256));

            // get attributes
            byte[] docBytes = sgn.getAuthenticatedAttributeBytes(nakeHash,  PdfSigner.CryptoStandard.CMS, _crlBytesList, _crlBytesList);
            // hash it again
            try(InputStream myInputStream = new ByteArrayInputStream(docBytes);){ 
                byte[] docBytesHash = DigestAlgorithms.digest(myInputStream, digest.getMessageDigest("SHA256"));

                //prepend sha256 prefix to hash for send signed
                hashToBeSignedByAma = new byte[_sha256SigPrefix.length + docBytesHash.length];
                System.arraycopy(_sha256SigPrefix, 0, hashToBeSignedByAma, 0, _sha256SigPrefix.length );
                System.arraycopy(docBytesHash, 0, hashToBeSignedByAma, _sha256SigPrefix.length, docBytesHash.length );
    
                return new byte[0]; // empty array
            } 
        }catch (IOException | GeneralSecurityException ioe) {
            throw new RuntimeException(ioe);
        }
    }
}

我用签名的散列对临时PDF进行签名

public void setFinalSignPDF(byte[] HashSignedForAma_, byte[] nakedHashFromIntermediaryPdf_, TSAClientBouncyCastle tsaClient_) throws IOException, GeneralSecurityException{     

    try (OutputStream writer = new FileOutputStream(_finalPdf);) {
        PdfReader pdfReader = new PdfReader(_temporaryPdf);
        PdfDocument document = new PdfDocument(pdfReader);

        InjectAmaSignatureContainer finalContainer = new InjectAmaSignatureContainer(
                                                                HashSignedForAma_,
                                                                nakedHashFromIntermediaryPdf_,
                                                                tsaClient_);
        PdfSigner.signDeferred(document, _signatureFieldname, writer, finalContainer);
    }
}

//***** CLASS ****
class InjectAmaSignatureContainer implements IExternalSignatureContainer {

    private byte[] documentHash;
    private byte[] signature;
    private TSAClientBouncyCastle tsaClient;
    private byte[] dados = null;

    public InjectAmaSignatureContainer(byte[] signature_, byte[] documentHash_, TSAClientBouncyCastle tsaClient_) {
        signature = signature_;
        documentHash = documentHash_;
        tsaClient = tsaClient_;
    }
    
    public byte[] getDados() {
        return dados;
    }

    @Override
    public byte[] sign(InputStream is) throws GeneralSecurityException {
        BouncyCastleDigest digest = new BouncyCastleDigest();
        
        PdfPKCS7 sgn = new PdfPKCS7(null, 
                                    _chain, 
                                    DigestAlgorithms.SHA256, 
                                    null, 
                                    digest, 
                                    false);

        sgn.setExternalDigest(signature, null, "RSA");

        byte[] encodedSig = sgn.getEncodedPKCS7(documentHash, PdfSigner.CryptoStandard.CMS, tsaClient, _ocspBytesList, _crlBytesList);

        return encodedSig;
    }

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

谢谢

编辑：方法：Prepare4AmaSigningContainer中的错误修复

byte[] docBytes = sgn.getAuthenticatedAttributeBytes(nakeHash, PdfSigner.CryptoStandard.CMS, _ocspBytesList, _crlBytesList);

Answer 1

经过多次尝试和信息分析，我找到了这个链接示例iText代码

*****重要提示******
由于函数应在类的签名容器方法中“停止”，因此该示例根本无法解决问题。这种方法解决了以下问题：应用签名后文档已被更改或损坏。

PDF签名

private static final String input = "c:/tmp/ama/PDF-1.pdf";
private static final String output =  "c:/tmp/ama/signed_signed.pdf";


public static void main(String[] args) throws IOException, GeneralSecurityException {
    Security.addProvider(new BouncyCastleProvider());
    PdfReader          reader             = new PdfReader(input);
    OutputStream       fos                = new FileOutputStream(output);
    StampingProperties stampingProperties = new StampingProperties();
    //For any signature in the Pdf  but the first one, you need to use appendMode
    //        stampingProperties.useAppendMode();
    PdfSigner pdfSigner = new PdfSigner(reader, fos, stampingProperties);

     /*you can modify the signature appearance */
    PdfSignatureAppearance appearance = pdfSigner.getSignatureAppearance();
    appearance.setPageRect(new Rectangle(36, 508, 254, 200));
    appearance.setPageNumber(1);
    appearance.setLayer2FontSize(10f);
    appearance.setReason("Teste Assinatura");
    appearance.setLocation("Lisboa");

    IExternalSignatureContainer gsContainer = new GSSignatureContainer(PdfName.Adobe_PPKLite, PdfName.Adbe_pkcs7_detached);
    pdfSigner.signExternalContainer(gsContainer, 8049);
}

public class GSSignatureContainer implements IExternalSignatureContainer {

/* Signature dictionary. Filter and SubFilter.  */
private PdfDictionary sigDic;

public GSSignatureContainer( PdfName filter, PdfName subFilter) {
    sigDic = new PdfDictionary();
    sigDic.put(PdfName.Filter, filter);
    sigDic.put(PdfName.SubFilter, subFilter);
}

@Override
public byte[] sign(InputStream data) throws GeneralSecurityException {
    try {
        //get all certificates (3) from client via web service
        Certificate[] chain = new CallAMA().getCertificates();

        String hashAlgorithm = DigestAlgorithms.SHA256;//"SHA-256";
        BouncyCastleDigest digest = new BouncyCastleDigest();
        MessageDigest md = digest.getMessageDigest(hashAlgorithm);

        byte[]   hash = DigestAlgorithms.digest(data, md);
        PdfPKCS7 sgn  = new PdfPKCS7(null, chain, hashAlgorithm, null, digest, false);

        Collection<byte[]> ocsp = null;

        byte[] attributeBytes = sgn.getAuthenticatedAttributeBytes(hash, PdfSigner.CryptoStandard.CADES, ocsp, null);

         //criar sha256 message digest
        byte[] attributeBytesDigest = MessageDigest.getInstance(hashAlgorithm).digest(attributeBytes);

        /****************************************************
         * CALL client (AMA) -> receive SMS and signed hash *
         ****************************************************/
        byte[] signedHash = new CallAMA().getHashSignedByAma(attributeBytesDigest);
        sgn.setExternalDigest(signedHash, null, "RSA");

        ITSAClient tsaClient = null;//new GSTSAClient(access);
        return sgn.getEncodedPKCS7(hash, PdfSigner.CryptoStandard.CADES, tsaClient, ocsp, null);
    } catch (IOException | GeneralSecurityException de) {
        de.printStackTrace();
        throw new GeneralSecurityException(de);
    }
}

@Override
public void modifySigningDictionary(PdfDictionary signDic) {
    signDic.putAll(sigDic);
}

}

Answer 2

这是我解决这个问题的方法。感谢MKL提供的提示。。。

private static final String input = "c:/tmp/ama/PDF-1.pdf";
private static final String tmp = "c:/tmp/ama/tmpPDF.pdf";
private static final String output =  "c:/tmp/ama/signed.pdf";

public static void main(String[] args) throws IOException, GeneralSecurityException {
    BouncyCastleProvider providerBC = new BouncyCastleProvider();
    Security.addProvider(providerBC);

    //get (via web service) all certificate (3 at all)
    Certificate[] chain = new CallAMA().getCertificates();

    StackOverflow app = new StackOverflow();
    
    //read the HASH to be signed (via web service) and create a tmp pdf. 
    byte[] hash4Sign = app.emptySignature(input, tmp, "sig", chain);
    
    //Concatenate the sha256SigPrefix to the hash and send it to be signed (via web service)
    //wait for the code received via SMS
    //(accepts the code via the keyboard and sends it via webservice)
    //finally receive the signed hash 
    byte[] signedHash = new CallAMA().getHashSignedByAma(hash4Sign);
    
    //insert hash in tmp pdf, and create a new pdf signed
    app.createSignature(signedHash, tmp, output, "sig", chain);
}

public byte[] emptySignature(String src, String dest, String fieldname, Certificate[] chain) throws IOException, GeneralSecurityException {
    PdfReader reader = new PdfReader(src);
    PdfSigner signer = new PdfSigner(reader, new FileOutputStream(dest), new StampingProperties().useAppendMode());
    PdfSignatureAppearance appearance = signer.getSignatureAppearance();

    appearance
            .setLayer2FontSize(6)
            .setPageRect(new Rectangle(36, 748, 250, 50))
            .setPageNumber(1)
            .setCertificate(chain[0])
            .setSignatureCreator("ORIGEM");
    signer.setFieldName(fieldname);
        
    /* ExternalBlankSignatureContainer constructor will create the PdfDictionary for the signature
     * information and will insert the /Filter and /SubFilter values into this dictionary.
     * It will leave just a blank placeholder for the signature that is to be inserted later.
     */
    MyExternalBlankSignatureContainer external = new MyExternalBlankSignatureContainer(chain, PdfName.Adobe_PPKLite, PdfName.Adbe_pkcs7_detached);

   
    // Sign the document using an external container.
    // 8192 is the size of the empty signature placeholder.
    signer.signExternalContainer(external, 8192);
    byte[] hash4Sign = external.getHash4Sign();
    return hash4Sign;
}

public void createSignature(byte[] hashSigned, String src, String dest, String fieldName, Certificate[] chain)
        throws IOException, GeneralSecurityException {
    PdfReader reader = new PdfReader(src);
    try(FileOutputStream os = new FileOutputStream(dest)) {
        PdfSigner signer = new PdfSigner(reader, os, new StampingProperties());

        IExternalSignatureContainer external = new MyExternalSignatureContainer(hashSigned, chain, PdfName.Adobe_PPKLite, PdfName.Adbe_pkcs7_detached);

        // Signs a PDF where space was already reserved. The field must cover the whole document.
        signer.signDeferred(signer.getDocument(), fieldName, os, external);
    }
}

class MyExternalSignatureContainer implements IExternalSignatureContainer {

    /* Signature dictionary. Filter and SubFilter.  */
    private PdfDictionary sigDic;
    private byte[] signedHash =null;
    private Certificate[] chain = null;

    public MyExternalSignatureContainer(byte[] _signedHash, Certificate[] _chain, PdfName filter, PdfName subFilter) {
        sigDic = new PdfDictionary();
        sigDic.put(PdfName.Filter, filter);
        sigDic.put(PdfName.SubFilter, subFilter);
        signedHash = _signedHash;
        chain = _chain;
    }

    @Override
    public byte[] sign(InputStream data) throws GeneralSecurityException {
        try {
            String hashAlgorithm = DigestAlgorithms.SHA256;//"SHA-256";
            BouncyCastleDigest digest = new BouncyCastleDigest();
            MessageDigest md = digest.getMessageDigest(hashAlgorithm);

            byte[]   hash = DigestAlgorithms.digest(data, md);
            PdfPKCS7 sgn  = new PdfPKCS7(null, chain, hashAlgorithm, null, digest, false);

            //Collection<byte[]> ocsp = new OcspClientBouncyCastle(null);
            OcspClientBouncyCastle ocspClient = new OcspClientBouncyCastle(null);
            Collection<byte[]> ocsp = new ArrayList<byte[]>();
            for(var i = 0; i < chain.length - 1; i++) {
                byte[] encoded = ocspClient.getEncoded((X509Certificate)chain[i], (X509Certificate)chain[i + 1], null);
                if(encoded != null) ocsp.add(encoded);
            }

            sgn.setExternalDigest(signedHash, null, "RSA");

            ITSAClient tsaClient = null;//new GSTSAClient(access);
            return sgn.getEncodedPKCS7(hash, PdfSigner.CryptoStandard.CADES, tsaClient, ocsp, null);
        } catch (IOException | GeneralSecurityException de) {
            de.printStackTrace();
            throw new GeneralSecurityException(de);
        }
    }

    @Override
    public void modifySigningDictionary(PdfDictionary signDic) {
        signDic.putAll(sigDic);
    }
}


class MyExternalBlankSignatureContainer implements IExternalSignatureContainer {

    /* Signature dictionary. Filter and SubFilter.  */
    private PdfDictionary sigDic;
    private byte[] hash4Sign = null;
    private Certificate[] chain = null;

    public MyExternalBlankSignatureContainer(Certificate[] _chain, PdfName filter, PdfName subFilter) {
        sigDic = new PdfDictionary();
        sigDic.put(PdfName.Filter, filter);
        sigDic.put(PdfName.SubFilter, subFilter);
        chain = _chain;
    }
    
    public byte[] getHash4Sign() {
        return hash4Sign;
    }

    @Override
    public byte[] sign(InputStream data) throws GeneralSecurityException {
        try {
            String hashAlgorithm = DigestAlgorithms.SHA256;//"SHA-256";
            BouncyCastleDigest digest = new BouncyCastleDigest();
            MessageDigest md = digest.getMessageDigest(hashAlgorithm);

            byte[]   hash = DigestAlgorithms.digest(data, md);
            PdfPKCS7 sgn  = new PdfPKCS7(null, chain, hashAlgorithm, null, digest, false);

            OcspClientBouncyCastle ocspClient = new OcspClientBouncyCastle(null);
            Collection<byte[]> ocsp = new ArrayList<byte[]>();
            for(var i = 0; i < chain.length - 1; i++) {
                byte[] encoded = ocspClient.getEncoded((X509Certificate)chain[i], (X509Certificate)chain[i + 1], null);
                if(encoded != null) ocsp.add(encoded);
            }

            byte[] attributeBytes = sgn.getAuthenticatedAttributeBytes(hash, PdfSigner.CryptoStandard.CADES, ocsp, null);

             //create sha256 message digest
            hash4Sign = MessageDigest.getInstance(hashAlgorithm).digest(attributeBytes);

            return new byte[0];
        } catch (IOException | GeneralSecurityException de) {
            de.printStackTrace();
            throw new GeneralSecurityException(de);
        }
    }

    @Override
    public void modifySigningDictionary(PdfDictionary signDic) {
        signDic.putAll(sigDic);
    }
}