XOR operation with two strings in java

Question

How to do bitwise XOR operation to two strings in java.

Answer 1

You want something like this:

import sun.misc.BASE64Decoder; import sun.misc.BASE64Encoder; import java.io.IOException;  public class StringXORer {      public String encode(String s, String key) {         return base64Encode(xorWithKey(s.getBytes(), key.getBytes()));     }      public String decode(String s, String key) {         return new String(xorWithKey(base64Decode(s), key.getBytes()));     }      private byte[] xorWithKey(byte[] a, byte[] key) {         byte[] out = new byte[a.length];         for (int i = 0; i < a.length; i++) {             out[i] = (byte) (a[i] ^ key[i%key.length]);         }         return out;     }      private byte[] base64Decode(String s) {         try {             BASE64Decoder d = new BASE64Decoder();             return d.decodeBuffer(s);         } catch (IOException e) {throw new RuntimeException(e);}     }      private String base64Encode(byte[] bytes) {         BASE64Encoder enc = new BASE64Encoder();         return enc.encode(bytes).replaceAll("\\s", "");      } } 

The base64 encoding is done because xor'ing the bytes of a string may not give valid bytes back for a string.

Answer 2

Note: this only works for low characters i.e. below 0x8000, This works for all ASCII characters.

I would do an XOR each charAt() to create a new String. Like

String s, key;  StringBuilder sb = new StringBuilder(); for(int i = 0; i < s.length(); i++)     sb.append((char)(s.charAt(i) ^ key.charAt(i % key.length()))); String result = sb.toString(); 

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In response to @user467257's comment

If your input/output is utf-8 and you xor "a" and "æ", you are left with an invalid utf-8 string consisting of one character (decimal 135, a continuation character).

It is the char values which are being xor'ed, but the byte values and this produces a character whichc an be UTF-8 encoded.

public static void main(String... args) throws UnsupportedEncodingException {     char ch1 = 'a';     char ch2 = 'æ';     char ch3 = (char) (ch1 ^ ch2);     System.out.println((int) ch3 + " UTF-8 encoded is " + Arrays.toString(String.valueOf(ch3).getBytes("UTF-8"))); } 

prints

135 UTF-8 encoded is [-62, -121]