BadPaddingException during decryption in java

Question

I am new java to encryption. Trying to implement something light weight to encrypt a string and store it somewhere and de-crypt it back before using.

With some web search I came up with this for encryption and decryption.

   public static String base64Encode(byte[] bytes)
    {
        return new BASE64Encoder().encode(bytes);
    }

   public static byte[] base64Decode(String property) throws IOException
    {
        return new BASE64Decoder().decodeBuffer(property);
    }


    public static String encrypt(String mystring) throws GeneralSecurityException, UnsupportedEncodingException
       {
        SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("PBEWithMD5AndDES");
        SecretKey key = keyFactory.generateSecret(new PBEKeySpec(mystring.toCharArray()));
        Cipher pbeCipher = Cipher.getInstance("PBEWithMD5AndDES");
        pbeCipher.init(Cipher.ENCRYPT_MODE, key, new PBEParameterSpec(SALT, 20));
        return base64Encode(pbeCipher.doFinal(mystring.getBytes("UTF-8")));
        }

    public static String decrypt(String estring) throws GeneralSecurityException, IOException
        {
        SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("PBEWithMD5AndDES");
        SecretKey key = keyFactory.generateSecret(new PBEKeySpec(estring.toCharArray()));
        Cipher pbeCipher = Cipher.getInstance("PBEWithMD5AndDES");
        pbeCipher.init(Cipher.DECRYPT_MODE, key, new PBEParameterSpec(SALT, 20));
        return new String(pbeCipher.doFinal(base64Decode(estring)), "UTF-8");
        }

I see that encryption worked but I saw a padding related exception in the decryption part, from the doFinal block. Here it is...

 encrypted string:zdrtgOKfkZMgpCOflr1ILQ==  -> Encrypted String
 exceptionjavax.crypto.BadPaddingException: Given
 final block not properly padded -> Exception from the doFinal block.

Seems like when I encrypted it, I need to do some kind of padding.

Can any one tell me what went wrong and how can it be fixed?

Thanks

Tas

Answer 1

You are using password based encryption here. This means that the encryption key itself is based upon a password. You must use the same password for both encryption and decryption.

private static char[] ENCRYPTION_PASSWORD
     = "some password populated by configuration".toCharArray();

public static String encrypt(String mystring)
  throws GeneralSecurityException, UnsupportedEncodingException {
    SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("PBEWithMD5AndDES");
    SecretKey key = keyFactory.generateSecret(new PBEKeySpec(ENCRYPTION_PASSWORD));
    Cipher pbeCipher = Cipher.getInstance("PBEWithMD5AndDES");
    pbeCipher.init(Cipher.ENCRYPT_MODE, key, new PBEParameterSpec(SALT, 20));
    return DatatypeConverter
        .printBase64Binary(pbeCipher.doFinal(mystring.getBytes("UTF-8")));
}

public static String decrypt(String string)
  throws GeneralSecurityException, IOException {
    SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("PBEWithMD5AndDES");
    SecretKey key = keyFactory.generateSecret(new PBEKeySpec(ENCRYPTION_PASSWORD));
    Cipher pbeCipher = Cipher.getInstance("PBEWithMD5AndDES");
    pbeCipher.init(Cipher.DECRYPT_MODE, key, new PBEParameterSpec(SALT, 20));
    return new String(pbeCipher.doFinal(DatatypeConverter
                                           .parseBase64Binary(estring)), "UTF-8");
}

Note also the use of javax.xml.bind.DatatypeConverter for base64 operations. No need to write your own or use third parties these days.

Answer 2

You will need to first decode your input to the decrypt method.

Call the base64Decode method and the estring parameter in your decrypt method.

That should do it.

Answer 3

Change your code ,

SecretKey key = keyFactory.generateSecret(new PBEKeySpec(mystring.toCharArray()));

to

SecretKey key = keyFactory.generateSecret(new PBEKeySpec("PASSWORD".toCharArray(), SALT, 20));