如何在java中读/写XORed txt文件UTF8？

Question

what i did so far :

I read a file1 with text, XORed the bytes with a key and wrote it back to another file2. My problem: I read for example 'H' from file1 , the byte value is 72;

72 XOR -32 = -88 Now i wrote -88 in to the file2. when i read file2 i should get -88 as first byte, but i get -3.

public byte[] readInput(String File) throws IOException {

    Path path = Paths.get(File);
    byte[] data = Files.readAllBytes(path);
    byte[]x=new byte[data.length ];

    FileInputStream fis = new FileInputStream(File);
    InputStreamReader isr = new InputStreamReader(fis);//utf8
    Reader in = new BufferedReader(isr);
    int ch;
    int s = 0;
    while ((ch = in.read()) > -1) {// read till EOF
        x[s] = (byte) (ch);
    }
    in.close();

    return x;


}




public void writeOutput(byte encrypted [],String file) {
    try {

        FileOutputStream fos = new FileOutputStream(file);
        Writer out = new OutputStreamWriter(fos,"UTF-8");//utf8

        String s = new String(encrypted, "UTF-8");

        out.write(s);
        out.close();
    }
    catch (IOException e) {
        e.printStackTrace();
    }
}



 public byte[]DNcryption(byte[]key,byte[] mssg){

    if(mssg.length==key.length)
    {
        byte[] encryptedBytes= new byte[key.length];

        for(int i=0;i<key.length;i++)
        {
            encryptedBytes[i]=Byte.valueOf((byte)(mssg[i]^key[i]));//XOR

        }
        return encryptedBytes;
    }
    else
    {
        return null;
    }

}   

Answer 1

You're not reading the file as bytes - you're reading it as characters . The encrypted data isn't valid UTF-8-encoded text, so you shouldn't try to read it as such.

Likewise, you shouldn't be writing arbitrary byte arrays as if they're UTF-8-encoded text.

Basically, your methods have signatures accepting or returning arbitrary binary data - don't use Writer or Reader classes at all . Just write the data straight to the stream. (And don't swallow the exception, either - do you really want to continue if you've failed to write important data?)

I would actually remove both your readInput and writeOutput methods entirely. Instead, use Files.readAllBytes and Files.write .

Answer 2

In writeOutput method you convert encrypted byte array into UTF-8 String which changes the actual bytes you are writing later to the file. Try this code snippet to see what is happening when you try to convert byte array with negative values to UTF-8 String:

final String s = new String(new byte[]{-1}, "UTF-8");
System.out.println(Arrays.toString(s.getBytes("UTF-8")));

It will print something like [-17, -65, -67] . Try using OutputStream to write bytes to the file.

new FileOutputStream(file).write(encrypted);