encrypt/decrypt file and Incorrect data

Question

static void encrypt() throws IOException, NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException {
    // Here you read the cleartext.
    FileInputStream fis = new FileInputStream("data/cleartext");
    // This stream write the encrypted text. This stream will be wrapped by another stream.
    FileOutputStream fos = new FileOutputStream("data/encrypted");

    // Length is 16 byte
    SecretKeySpec sks = new SecretKeySpec("MyDifficultPassw".getBytes(), "AES");
    // Create cipher
    Cipher cipher = Cipher.getInstance("AES");
    cipher.init(Cipher.ENCRYPT_MODE, sks);
    // Wrap the output stream
    CipherOutputStream cos = new CipherOutputStream(fos, cipher);
    // Write bytes
    int b;
    byte[] d = new byte[8];
    while((b = fis.read(d)) != -1) {
        cos.write(d, 0, b);
    }
    // Flush and close streams.
    cos.flush();
    cos.close();
    fis.close();
}

---

static void decrypt() throws IOException, NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException {
    FileInputStream fis = new FileInputStream("data/encrypted");

    FileOutputStream fos = new FileOutputStream("data/decrypted");
    SecretKeySpec sks = new SecretKeySpec("MyDifficultPassw".getBytes(), "AES");
    Cipher cipher = Cipher.getInstance("AES");
    cipher.init(Cipher.DECRYPT_MODE, sks);
    CipherInputStream cis = new CipherInputStream(fis, cipher);
    int b;
    byte[] d = new byte[8];
    while((b = cis.read(d)) != -1) {
        fos.write(d, 0, b);
    }
    fos.flush();
    fos.close();
    cis.close();
}   

I am using these functions for encrypt/ decrypt file, but on some devices I get incorrect data.

for example, my correct data is :

one

two

three

four

five

after decrypt :

one

two

three

൰Ẓ㫩

൰Ẓ㫩

I have used postDelayed() function But it did not matter !

 decrypt();
new Handler().postDelayed(new Runnable() {

    @Override
    public void run() {
    // TODO Auto-generated method stub

            getContentsFile();
            }
        }, 7000);

the file size is 80 Kilobytes!

it had problem on emulator!! it had problem on samsung gt-s7562, but on galaxy s4 everything is ok !!

Answer 1

I see at least two potential platform compatibility issues with your code:

1. Never call getBytes() without declaring a charset:

   SecretKeySpec sks = new SecretKeySpec("MyDifficultPassw".getBytes(), "AES");
   

   should be: (e.g.)

   SecretKeySpec sks = new SecretKeySpec(
       "MyDifficultPassw".getBytes("UTF-8"), "AES");
   

2. Always specify a complete transformation, e.g. "AES/CBC/PKCS5Padding":

   Cipher cipher = Cipher.getInstance("AES");
   

   should be (e.g.)

   Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
   

This alone could be the cause of your problem. Different platforms have different default character sets, which means you would get a different string of bytes for your key.

Less commonly, different crypto providers have different defaults when you selet "AES". Some will do ECB-mode encryption, some will do CBC-mode encryption. It's always safest to declare exactly what you want.

---

Side note: you really shouldn't be creating a key from the raw bytes of a string. Use a password derivation method instead, such as PBKDF2.

Answer 2

I'm using these two methods for encrypt/decrypt and they work perfectly to me on any device. It's done a slightly different way than you so try comparing both approaches to see what could be working wrong.

For encryption:

Gets: iv vector and the message to encrypt:

public String getEncrypt(final byte[] iv, final String message) throws GeneralSecurityException, NullPointerException {
  if (key.isEmpty())
    throw new NullPointerException();

  final byte[] rawData = key.getBytes(Charset.forName("US-ASCII"));
  if (rawData.length != 16) {
    // If this is not 16 in length, there's a problem with the key size, nothing to do here
    throw new IllegalArgumentException("You've provided an invalid key size");
  }

  final SecretKeySpec seckeySpec = new SecretKeySpec(rawData, "AES");
  final Cipher ciph = Cipher.getInstance("AES/CBC/PKCS5Padding");

  ciph.init(Cipher.ENCRYPT_MODE, seckeySpec, new IvParameterSpec(iv));

  byte[] encryptedBA = ciph.doFinal(message.getBytes(Charset.forName("US-ASCII")));
  try {
    final String encryptedText = new String(Base64.encode(encryptedBA, Base64.DEFAULT), "UTF-8");
    return encryptedText.toString();
  } 
  catch (final UnsupportedEncodingException e1) { }
  return "";
}

For decryption:

public String getDecrypt(final byte[] encrypted) throws GeneralSecurityException, NullPointerException {
  if (key.isEmpty())
    throw new NullPointerException();

  final byte[] rawData = key.getBytes(Charset.forName("US-ASCII"));
  if (rawData.length != 16) {
    // If this is not 16 in length, there's a problem with the key size, nothing to do here
    throw new IllegalArgumentException("Invalid key size.");
  }

  final SecretKeySpec seckeySpec = new SecretKeySpec(rawData, "AES");

  final Cipher ciph = Cipher.getInstance("AES/CBC/PKCS5Padding");
  ciph.init(Cipher.DECRYPT_MODE, seckeySpec, new IvParameterSpec(new byte[16]));
  final byte[] decryptedmess = ciph.doFinal(encrypted);

  return new String(decryptedmess, Charset.forName("US-ASCII"));
}