Convert a file to encrypted file and decrypt it on server (Using Public key encryption)

Question

I am trying to encrypt/decrypt a file using RSA. But I can't see the data inside the file.

Here is the Code :

     // To encrypt a file 

  private static void encrypt(InputStream input, OutputStream output, PublicKey key)
        throws IOException, NoSuchAlgorithmException,   NoSuchPaddingException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException     {
    final Cipher encrypt = Cipher.getInstance(ALGORITHM);
  // encrypt the plain text using the public key
         encrypt.init(Cipher.ENCRYPT_MODE, key);
        // encrypt.doFinal();
    output = new CipherOutputStream(output,encrypt);
    writeBytes(input, output, encrypt);
            output.close();
}


    // To decrypt  the file

private static void decrypt(InputStream input, OutputStream output, PrivateKey key)
        throws IOException,NoSuchAlgorithmException,InvalidKeyException,NoSuchPaddingException,BadPaddingException,IllegalBlockSizeException {
        final Cipher decrypt = Cipher.getInstance(ALGORITHM);

  // decrypt the text using the private key
  decrypt.init(Cipher.DECRYPT_MODE, key);
    input = new CipherInputStream(input, decrypt);
    writeBytes(input, output, decrypt);
            input.close();
}

// To write on the file from the inputstream

private static void writeBytes(InputStream input, OutputStream output, Cipher cipher)
        throws IOException, IllegalBlockSizeException,BadPaddingException {
    byte[] writeBuffer = new byte[512];
    int readBytes = 0;

    while ((readBytes = input.read(writeBuffer)) >= 0) {
                System.out.println(readBytes);




               // String text = input.read(writeBuffer);
               // cipher.doFinal();
                try{
                    System.out.println("Here");
        output.write(writeBuffer, 0, readBytes);
                }
                catch(Exception e){
                e.printStackTrace();
                }
    }

    output.close();
    input.close();
}

Main Function :

  // Check if the pair of keys are present else generate those.
  if (!areKeysPresent()) {
    // Method generates a pair of keys using the RSA algorithm and stores it
    // in their respective files
    generateKey();
  }

  final String originalText = "Text to be encrypted ";
  ObjectInputStream inputStream = null;

  String clearFile = "/UploadFile/Log.txt";      
  String encryptedFile = "/UploadFile/LogE.txt";      
  String decryptedFile = "/UploadFile/LogD.txt";

  // Encrypt the string using the public key
  inputStream = new ObjectInputStream(new FileInputStream(PUBLIC_KEY_FILE));
  final PublicKey publicKey = (PublicKey) inputStream.readObject();
 // final byte[] cipherText = encrypt(originalText, publicKey);

  encrypt(new FileInputStream(clearFile), new FileOutputStream(encryptedFile), publicKey);
  System.out.println("Successfully Encrypted");

  }
  // Decrypt the cipher text using the private key.
  inputStream = new ObjectInputStream(new FileInputStream(PRIVATE_KEY_FILE));
  final PrivateKey privateKey = (PrivateKey) inputStream.readObject();
 // final String plainText = decrypt(cipherText, privateKey);

  decrypt(new FileInputStream(encryptedFile), new FileOutputStream(decryptedFile), privateKey);
  System.out.println("Successfully Decrypted");


GenerateKey Function : 

public static void generateKey() {
try {
  final KeyPairGenerator keyGen = KeyPairGenerator.getInstance(ALGORITHM);
  keyGen.initialize(1024);
  final KeyPair key = keyGen.generateKeyPair();

  File privateKeyFile = new File(PRIVATE_KEY_FILE);
  File publicKeyFile = new File(PUBLIC_KEY_FILE);

  // Create files to store public and private key
  if (privateKeyFile.getParentFile() != null) {
    privateKeyFile.getParentFile().mkdirs();
  }
  privateKeyFile.createNewFile();

  if (publicKeyFile.getParentFile() != null) {
    publicKeyFile.getParentFile().mkdirs();
  }
  publicKeyFile.createNewFile();

  // Saving the Public key in a file
  ObjectOutputStream publicKeyOS = new ObjectOutputStream(
      new FileOutputStream(publicKeyFile));
  publicKeyOS.writeObject(key.getPublic());
  publicKeyOS.close();

  // Saving the Private key in a file
  ObjectOutputStream privateKeyOS = new ObjectOutputStream(
      new FileOutputStream(privateKeyFile));
  privateKeyOS.writeObject(key.getPrivate());
  privateKeyOS.close();
} catch (Exception e) {
  e.printStackTrace();
}

  }

I am not getting any data in the encrypted as well as decrypted file.

clearFile is the original data file, encryptedFile is encrypted data, decryptedFile is decrypted data.

Please help, What I am missing here.

Answer 1

You don't use RSA for data encryption. You use it to encrypt a symmetric key, and use a symmetric key to encrypt your data. Public key algorithms are for key transport or key agreement, not data.

You should use a CMS (S/MIME) or PGP library for your application.