PDF Signing By p12 With JS

DocSignController.java

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@GetMapping("/doc-sign/sign")
public ResponseEntity<Resource> getHashForSign() throws IOException {
    log.debug("start to generate merged PDF in java web start program");
    synchronized (eventPublisher) {
        eventPublisher.publishEvent(new OnDocMergeEvent(getUserId(), getXxxFormMaster().getXxxFormMasterId(), getXxxFormMaster().getFormType()));
    }
    Integer xxxFormMasterId = getXxxFormMaster().getXxxFormMasterId();
    String userId = getUserId();

    List<SuppDoc> suppDocs = suppDocMapper.selectSuppDocByXxxFormMasterIdAndDocTypeAndUserId(xxxFormMasterId, userId, Constants.SUPP_DOC_TYPE_SYS_GEN_MERGE);
    if (suppDocs == null || suppDocs.isEmpty()) {
        suppDocs = suppDocMapper.selectSuppDocByXxxFormMasterIdAndDocTypeAndUserId(xxxFormMasterId, userId, Constants.SUPP_DOC_TYPE_SYS_SIGN);
        if (suppDocs != null && !suppDocs.isEmpty()) {
            log.info("signed doc exists !!");
            return ResponseEntity.status(HttpStatus.NOT_ACCEPTABLE).body(null);
        }
        return ResponseEntity.status(HttpStatus.NOT_FOUND).body(null);
    }

    SuppDoc suppDoc = suppDocs.get(0);
    Integer suppDocId = suppDoc.getSuppDocId();

    Resource pdfFile = storageService.loadAsResource(xxxFormMasterId, suppDocId);

    File tempPdfFile = File.createTempFile("tmp", ".pdf");
    log.debug("Prepare pdf file for sign: {}", tempPdfFile.getPath());

    log.info("get hash for sign, userId {} form master id {}", userId, xxxFormMasterId);

    InputStream is = null;
    try {
        is = emptySignature(pdfFile.getInputStream(), tempPdfFile);
    } catch (DocumentException | GeneralSecurityException e) {
        log.error("error occurrs on calculate signature", e);
    }

    byte[] encryptedEmptySig = encrypt(StreamUtils.copyToByteArray(is));
    //byte[] emptySig = StreamUtils.copyToByteArray(is);
    String emptySig = Base64.getEncoder().encodeToString(encryptedEmptySig);

    ByteArrayResource resource = new ByteArrayResource(emptySig.getBytes(StandardCharsets.ISO_8859_1));

    HttpHeaders headers = new HttpHeaders();
    headers.add("Cache-Control", "no-cache, no-store, must-revalidate");
    headers.add("Pragma", "no-cache");
    headers.add("Expires", "0");

    request.getSession(false).setAttribute(TEMP_SIGN_PATH, tempPdfFile.getPath());

    return ResponseEntity.ok()
            .headers(headers)
            .contentLength(resource.contentLength())
            .contentType(MediaType.TEXT_PLAIN)
            .body(resource);
}

private byte[] encrypt(byte[] emptySig) {
    /*try {
        log.debug("js debugging for signing with forge")
        log.debug("HexBin.encode(emptySig) " + HexBin.encode(emptySig).substring(0, 500));
        MessageDigest messageDigest = MessageDigest.getInstance("SHA-256");
        byte hash[] = messageDigest.digest(emptySig);
        System.out.println("server emptySig sha256 hash = " + Hex.toHexString(hash));
    } catch (NoSuchAlgorithmException e1) {
    }*/

    String type = "X.509";

    String encodedCertificate = request.getParameter("certificate");
    try {
        CertificateFactory certificateFactory = CertificateFactory.getInstance(type);
        Certificate certificate = certificateFactory.generateCertificate(
                new ByteArrayInputStream(HashUtils.base64Decode(encodedCertificate)));
        PublicKey publicKey = certificate.getPublicKey();

        Cipher rsaCipher;
        try {
            rsaCipher = Cipher.getInstance(RSA_ALGORITHM);
            rsaCipher.init(Cipher.ENCRYPT_MODE, publicKey);

            // reference from https://stackoverflow.com/questions/24338108/java-encrypt-string-with-existing-public-key-file
            // Now create a new 256 bit Rijndael key to encrypt the file itself.
            // This will be the session key.
            /*KeyGenerator rijndaelKeyGenerator = KeyGenerator.getInstance("Rijndael");
            rijndaelKeyGenerator.init(256);
            log.debug("Generating session key...");
            Key rijndaelKey = rijndaelKeyGenerator.generateKey();
            log.debug("Done generating key.");
            
            byte[] encodedKeyBytes = rsaCipher.doFinal(rijndaelKey.getEncoded());
            ByteArrayOutputStream output = new ByteArrayOutputStream();
            output.write(encodedKeyBytes.length);
            output.write(encodedKeyBytes);
            
            // Now we need an Initialization Vector for the symmetric cipher in CBC mode
            SecureRandom random = new SecureRandom();
            byte[] iv = new byte[16];
            random.nextBytes(iv);
            
            output.write(iv);
            
            IvParameterSpec spec = new IvParameterSpec(iv);
            // Create the cipher for encrypting the file itself.
            Cipher symmetricCipher = Cipher.getInstance(RIJNDAEL_ALGORITHM);
            symmetricCipher.init(Cipher.ENCRYPT_MODE, rijndaelKey, spec);
            */

            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            DataOutputStream output = new DataOutputStream(baos);

            KeyGenerator generator = KeyGenerator.getInstance("AES");
            generator.init(128);
            log.debug("Generating session key...");
            SecretKey aesKey = generator.generateKey();
            log.debug("Done generating key.");

            log.debug("aesKey.getEncoded() = " + Base64.getEncoder().encodeToString(aesKey.getEncoded()));
            byte[] encodedKeyBytes = rsaCipher.doFinal(aesKey.getEncoded());

            // output = encrypted AES key length + encrypted AES key + empty signature encrypted by AES key
            log.debug("encrypted AES key length = " + encodedKeyBytes.length);
            output.writeInt(encodedKeyBytes.length);
            output.write(encodedKeyBytes);

            Cipher symmetricCipher = Cipher.getInstance(AES_ALGORITHM);
            symmetricCipher.init(Cipher.ENCRYPT_MODE, aesKey);

            output.write(symmetricCipher.doFinal(emptySig));
            output.flush();

            log.debug("length of encrypted data = " + baos.toByteArray().length);
            return baos.toByteArray();
        } catch (NoSuchAlgorithmException | NoSuchPaddingException | InvalidKeyException
                | IllegalBlockSizeException | BadPaddingException | IOException e) {
            log.error("encrypt empty signature", e);
        }
    } catch (CertificateException e) {
        log.error("encrypt", e);
    }

    return null;
}

private InputStream emptySignature(InputStream src, File dest)
        throws IOException, DocumentException, GeneralSecurityException {
    PdfReader reader = new PdfReader(src);
    FileOutputStream os = new FileOutputStream(dest);
    PdfStamper stamper = PdfStamper.createSignature(reader, os, '\0');
    PdfSignatureAppearance appearance = stamper.getSignatureAppearance();

    //appearance.setVisibleSignature(new Rectangle(0, 0, 0, 0), 1, FIELD_NAME);
    log.info("create empty signature");
    String position = (String) WebUtils.getSession().getAttribute(WebAttributeNames.SESSION_PSCT_DOC_SIGNATURE_POSITION);
    String[] p = position.split("\\|");
    appearance.setVisibleSignature(new Rectangle(Float.valueOf(p[0]), Float.valueOf(p[1]), Float.valueOf(p[2]), Float.valueOf(p[3])), Integer.valueOf(p[4]), Constants.SIG_FIELD_NAME);

    // set signature text
    Font font = new Font(FontFamily.TIMES_ROMAN, 10, Font.BOLD);
    appearance.setLayer2Font(font);
    appearance.setRunDirection(PdfWriter.RUN_DIRECTION_RTL);

    appearance.setLayer2Text("Signed By Digital Certificate");

    ClassPathResource pinImage = new ClassPathResource("static/images/Cert-sign.png");
    appearance.setImage(Image.getInstance(pinImage.getURL()));

    //appearance.setCertificate(chain[0]);
    ExternalSignatureContainer external = new ExternalBlankSignatureContainer(PdfName.ADOBE_PPKLITE,
            PdfName.ADBE_PKCS7_DETACHED);
    MakeSignature.signExternalContainer(appearance, external, 8192);
    os.close();
    return appearance.getRangeStream();
}

@PostMapping(value = "/doc-sign/sign", produces = MediaType.APPLICATION_JSON_VALUE)
@ResponseBody
public CertSignResult attachSignedHash() {
    CertSignResult certSignResult = new CertSignResult();
    certSignResult.setStatus(CertSignResult.STATUS_NOT_SIGNED);

    try {
        if (!WebUtils.validateCert(pkiClient)) {
            return certSignResult;
        }
    } catch (Exception e) {
        log.error("signHash", e);
        return certSignResult;
    }

    String tempPath = (String) request.getSession(false).getAttribute(TEMP_SIGN_PATH);

    Integer xxxFormMasterId = getXxxFormMaster().getXxxFormMasterId();
    String userId = getUserId();

    log.info("sign hash, userId {} form master id {}", userId, xxxFormMasterId);

    //		tryToDeleteSignedDoc();

    File tempSignedFile = null;

    try {
        tempSignedFile = File.createTempFile("signed-" + xxxFormMasterId + "-", ".pdf");

        String hash = request.getParameter("signed");
        //log.debug("hash {}", hash);
        // Save the hash to file pkcs7-hash.pem
        // View p7 file content by: openssl asn1parse -inform pem -in pkcs7-hash.pem

        byte[] signedhash = Base64.getDecoder().decode(hash);

        createSignature(tempPath, tempSignedFile, signedhash);
    } catch (DocumentException | GeneralSecurityException | IOException e) {
        log.error("Fail to sign document " + e);
        return certSignResult;
    }

    SimpleSuppDoc doc = new SimpleSuppDoc();
    doc.setXxxFormMasterId(xxxFormMasterId);
    doc.setLocalFile(tempSignedFile);
    doc.setSuppDocType(Constants.SUPP_DOC_TYPE_SYS_SIGN);

    try {
        Integer suppDocId = storageService.store(doc, userId);

        if (doc.isUploadSucess()) {
            insertSigningLog(userId, xxxFormMasterId, suppDocId);

            // no need to keep the merged doc
            storageService.deleteDocByUserIdAndType(xxxFormMasterId, userId, Constants.SUPP_DOC_TYPE_SYS_GEN_MERGE);

            certSignResult.setStatus(CertSignResult.STATUS_SIGNED);
            request.getSession(false).setAttribute(WebAttributeNames.SESSION_PSCT_DOC_SIGN_STATUS, certSignResult);

            createZipFileForSignedDoc(userId, tempSignedFile);
            return certSignResult;
        }
    } catch (IOException e) {
        log.error("sign pdf file", e);
    } finally {
        if (tempSignedFile != null)
            tempSignedFile.delete();
    }

    return certSignResult;
}

private void createSignature(String src, File dest, byte[] signedHash)
        throws IOException, DocumentException, GeneralSecurityException {
    PdfReader reader = new PdfReader(src);
    FileOutputStream os = new FileOutputStream(dest);
    ExternalSignatureContainer external = new MyExternalSignatureContainer(signedHash);
    MakeSignature.signDeferred(reader, Constants.SIG_FIELD_NAME, os, external);
    os.close();
}

class MyExternalSignatureContainer implements ExternalSignatureContainer {
    protected byte[] sig;

    public MyExternalSignatureContainer(byte[] sig) {
        this.sig = sig;
    }

    @Override
    public void modifySigningDictionary(PdfDictionary signDic) {
    }

    @Override
    public byte[] sign(InputStream arg0) throws GeneralSecurityException {
        return sig;
    }
}

JS for PDF signing

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function signAndSubmit() {
  console.log("signAndSubmit")

  var idType = $(":radio[name='idType']:checked").val();
  var hkid = $("#hkid").val();
  var hkidCheckDigit = $("#hkidCheckDigit").val();
  var passport = $("#passport").val()
  var file = document.getElementById("filename").files[0];

  if (!checkInput(idType, hkid, hkidCheckDigit, passport, file))
    return false;

  var password = $("#pin").val();
  console.log("password " + password)

  //Reading certificate from a 'file' form field
  var reader = new FileReader();
  reader.onload = function (e) {
    var contents = e.target.result;

    var pkcs12 = loadFile(password, contents);
    if(!pkcs12){
      showError(ErrorCode.INVALID_PIN);
      return false;
    }

    extractInfo(pkcs12, idType, hkid, hkidCheckDigit, passport).then(function (info) {
      var data = {
        signature: info.signature,
        // certLogin: "1",
        certificate: info.certificate,
        hkid: hkid + ":" + hkidCheckDigit,
        passport: passport,
        idType: idType,
      };

    $.ajax({
        type: 'GET',
        url: resetStatusUrl + "?keep-challenge=1",
        dataType: 'json',
        async: false,
        success: function(result) {
            if (result == 0) {
                console.log("start to do signing for the PDF");
            }
        },
        error: function(exception) {
          window.location.href = errPath;
        }
    });

    $.get(validateUserUrl, { hkid: data.hkid, passport: data.passport, idType: data.idType }).done(function (result) {
        if (result == 'T') {
          $.get(signAndSubmitUrl, { certificate: data.certificate }).done(function (signature) {
            console.log("signature = " + signature.length);
            var ciphertext = forge.util.decode64(signature);

            var buffer = forge.util.createBuffer(ciphertext, 'binary');

            var aesKeyLength = buffer.getInt32();
            console.log("aesKeyLength = " + aesKeyLength);

            var encryptedAesKey = buffer.getBytes(aesKeyLength);
            console.dir(encryptedAesKey);

            var aesKey = privateKey.decrypt(encryptedAesKey);
            console.log("decrypted aesKey = " + forge.util.encode64(aesKey));

            var decipher = forge.cipher.createDecipher('AES-ECB', aesKey);
            decipher.start();
            decipher.update(forge.util.createBuffer(buffer.getBytes()));

            var result = decipher.finish(); // check 'result' for true/false
            console.log("result = " + result);
            // outputs decrypted hex
            // console.log("outputs decrypted hex = " + decipher.output.toHex());

            var emptySig = decipher.output.getBytes();

            /* debug for signing
            var md = forge.md.sha256.create();
            var sh = md.update(decipher.output.getBytes()).digest().toHex();
            console.log("origEmptySig sha256 hash = " + sh);
            var sh = privateKey.sign(md.update(decipher.output.getBytes()))
            */

            var p7 = forge.pkcs7.createSignedData();
            p7.content = "Arbitrary data"; // privateKey.sign(md.update(decipher.output.getBytes()));

            let _cert; // individual's e-cert
            if (info.ca.indexOf('HKPOST') != -1) {
              _cert = certChain[0];
              certChain.reverse();
            } else {
              _cert = certChain.slice(-1)[0]
            }

            // e-cert order: root cert, intermediate cert, individual cert
            for (var i = 0; i <= certChain.length - 1; i++) {
              p7.addCertificate(certChain[i]);
            }

            p7.addSigner({
              key: privateKey,
              certificate: _cert,
              digestAlgorithm: forge.pki.oids.sha256,
              authenticatedAttributes: [{
                type: forge.pki.oids.contentType,
                value: forge.pki.oids.data
              }, {
                type: forge.pki.oids.messageDigest,
                value: emptySig // custom digest
              }, {
                type: forge.pki.oids.signingTime,
                value: new Date()
              }]
            });


            p7.sign({ detached: true });

            //var out = forge.asn1.toDer(p7.toAsn1()).getBytes();
            var out = forge.pkcs7.messageToPem(p7)
            // console.log(out);
            //var signedHash = forge.util.encode64(out);
            signedHash = out.replace("-----BEGIN PKCS7-----", "").replace("-----END PKCS7-----", "").split("\r\n").join("");
            //console.dir(signedHash);

            data.signed = signedHash;
            // console.dir(data);

            $.post(signAndSubmitUrl, data, function (result) {
              //alert("sign result " + result.status);
              if (result.status == "F") {
                showError(-131);
              } else {
                showMessage("doc.sign.success");
              }
            });
          }).fail(function(xhr, statusText, error){
              //alert("error status code " + xhr.status);
              if (xhr.status == 406) {
                  showError(-134);
              } else if (xhr.status == 404) {
                 showError(-133);
              }
          });
        } else {
          showError(-138);
        }
      });
    }).catch(function (info) {
      console.log("error code : " + info.errCode);
      showError(info.errCode);
    });
  }

  reader.readAsArrayBuffer(file);
  return false;
}

following code writtern was studied by the result from openssl asn1parse -inform pem -in pkcs7-hash.pem

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for (var i = 0; i <= certChain.length - 1; i++) {
  p7.addCertificate(certChain[i]);
}

p7.addSigner({
  key: privateKey,
  certificate: _cert,
  digestAlgorithm: forge.pki.oids.sha256,
  authenticatedAttributes: [{
    type: forge.pki.oids.contentType,
    value: forge.pki.oids.data
  }, {
    type: forge.pki.oids.messageDigest,
    value: emptySig // custom digest
  }, {
    type: forge.pki.oids.signingTime,
    value: new Date()
  }]
});


p7.sign({ detached: true });

forge.js was hacked by adding following code

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for(var ai = 0; ai < signer.authenticatedAttributes.length; ++ai) {
  var attr = signer.authenticatedAttributes[ai];
  if(attr.type === forge.pki.oids.messageDigest) {
    // use content message digest as value
    // attr.value = mds[signer.digestAlgorithm].digest();

    // ++++++++ change for setting a custom digest for PDF signing
    var digest = mds[signer.digestAlgorithm].start().update(attr.value).digest();
    attr.value = digest;
    // ++++++++ 

  } else if(attr.type === forge.pki.oids.signingTime) {
    // auto-populate signing time if not already set
    if(!attr.value) {
      attr.value = signingTime;
    }
  }

AuthenticationApplet.java (itext for PDF signing), below code is as the reference for study on PDF signing with js

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public String signDoc(String emptySig, String keyID, String type, String privateKeyPassword) {
    if (privateKeyPassword == null || "".equals(privateKeyPassword.trim())) {
        privateKeyPassword = m_password;
    }

    if ("p12".equals(type)) {
        m_providerName = "BC";
    }

    PrivateKey privateKey = null;
    try {
        privateKey = (PrivateKey) m_keyStore.getKey(keyID, privateKeyPassword.toCharArray());
    } catch (UnrecoverableKeyException | KeyStoreException | NoSuchAlgorithmException e1) {
        e1.printStackTrace();
    }

    String signHashStr = "";

    try {
        //byte[] origEmptySig = Base64.getUrlDecoder().decode(emptySig);
        byte[] origEmptySig = decrypt(Base64.getDecoder().decode(emptySig), privateKey);
        // System.out.println("Showing information for debugging PDF signing using javascript
        // System.out.println("origEmptySig = " + Hex.toHexString(origEmptySig).substring(0, 300));

        ByteArrayInputStream emptySignature = new ByteArrayInputStream(origEmptySig);

        Security.addProvider(new BouncyCastleProvider());

        PrivateKeySignature signature = new PrivateKeySignature(privateKey, "SHA256", m_providerName);
        String hashAlgorithm = signature.getHashAlgorithm();

        System.out.println("hashAlgorithm = " + hashAlgorithm);
        BouncyCastleDigest digest = new BouncyCastleDigest();
        Certificate[] certificateChain = retrieveCertificateChain(keyID);

        /*String oid = DigestAlgorithms.getAllowedDigests(hashAlgorithm);
        System.out.println("oid = " + oid);*/

        MessageDigest messageDigest = digest.getMessageDigest(hashAlgorithm);
        byte hash[] = DigestAlgorithms.digest(emptySignature, messageDigest);

        //MessageDigest messageDigest = MessageDigest.getInstance("SHA-256");
        //byte hash[] = messageDigest.digest(origEmptySig);

        // System.out.println("origEmptySig sha256 hash = " + Hex.toHexString(hash));

        PdfPKCS7 sgn = new PdfPKCS7(null, certificateChain, hashAlgorithm, null, digest, false);
        Calendar cal = Calendar.getInstance();
        byte[] sh = sgn.getAuthenticatedAttributeBytes(hash, cal, null, null, CryptoStandard.CMS);
        //System.out.println("AuthenticatedAttributeBytes sha256 hash = " + Hex.toHexString(sh));

        byte[] extSignature = signature.sign(sh);
        //System.out.println("signed AuthenticatedAttributeBytes = " + Hex.toHexString(hash));

        sgn.setExternalDigest(extSignature, null, signature.getEncryptionAlgorithm());
        byte[] signHash = sgn.getEncodedPKCS7(hash, cal, null, null, null, CryptoStandard.CMS);

        // System.out.println("signHash = " + Hex.toHexString(signHash).substring(0, 300));

        signHashStr = Base64.getEncoder().encodeToString(signHash);
        //Files.write(Paths.get("D:/pkcs7-hash.p7b"), signHash, StandardOpenOption.CREATE);

        //System.out.println("signHash = " + signHashStr);
    } catch (Exception e) {
        System.err.println("An unknown error on calculating hash for signature: " + e.getMessage());
        e.printStackTrace();
    }

    return signHashStr;
}

private static final String RSA_ALGORITHM = "RSA/ECB/PKCS1Padding";
private static final String AES_ALGORITHM = "AES/ECB/PKCS5Padding";

private byte[] decrypt(byte[] ciphertext, PrivateKey privateKey) throws IOException {
    try {
        Cipher rsaCipher = Cipher.getInstance(RSA_ALGORITHM);
        rsaCipher.init(Cipher.DECRYPT_MODE, privateKey);

        DataInputStream dis = new DataInputStream(new ByteArrayInputStream(ciphertext));

        byte[] encryptedKeyBytes = new byte[dis.readInt()];

        dis.readFully(encryptedKeyBytes);

        byte[] aesKeyBytes = rsaCipher.doFinal(encryptedKeyBytes);

        SecretKeySpec key = new SecretKeySpec(aesKeyBytes, "AES");
        Cipher cipher = Cipher.getInstance(AES_ALGORITHM);
        cipher.init(Cipher.DECRYPT_MODE, key);

        ByteArrayOutputStream output = new ByteArrayOutputStream();
        int len = -1;
        byte[] buffer = new byte[4096];

        while ((len = dis.read(buffer, 0, buffer.length)) != -1) {
            output.write(buffer, 0, len);
        }

        output.flush();

        return cipher.doFinal(output.toByteArray());
    } catch (Exception e) {
        System.err.println("An unknown error on decrypt key: " + e.getMessage());
    }

    return null;
}

Reference

https://security.stackexchange.com/questions/73156/whats-the-difference-between-x-509-and-pkcs7-certificate
https://security.stackexchange.com/questions/41399/openssl-pkcs7-vs-s-mime
https://crypto.stackexchange.com/questions/37084/is-pkcs7-a-signature-format-or-a-certificate-format

openssl asn1parse -inform pem -in pkcs7-hash.pem
Manual verify PKCS#7 signed data with OpenSSL