Question

Let’s say I have a plain text a nice cup of milk tea, which is going to be XOR cipher-ed with key 12345.

This Java code:

import sun.misc.BASE64Encoder;

import sun.misc.BASE64Decoder;

public class XORTest {

  public static void main(String args[]){

    String plaintext = "a nice cup of milk tea";
    String key = "12345";
    String encrypted = xor_encrypt(plaintext, key);
    String decrypted = xor_decrypt(encrypted, key);
    System.out.println("Encrypted: "+encrypted);
    System.out.println("Decrypted: "+decrypted);
  }

  public static String xor_encrypt(String message, String key){
    try {
      if (message==null || key==null ) return null;

      char[] keys=key.toCharArray();
      char[] mesg=message.toCharArray();
      BASE64Encoder encoder = new BASE64Encoder();

      int ml=mesg.length;
      int kl=keys.length;
      char[] newmsg=new char[ml];

      for (int i=0; i<ml; i++){
        newmsg[i]=(char)(mesg[i]^keys[i%kl]);
      }
      mesg=null; 
      keys=null;
      String temp = new String(newmsg);
      return new String(new BASE64Encoder().encodeBuffer(temp.getBytes()));
    }
    catch ( Exception e ) {
      return null;
    }  
  }
  

  public static String xor_decrypt(String message, String key){
    try {
      if (message==null || key==null ) return null;
      BASE64Decoder decoder = new BASE64Decoder();
      char[] keys=key.toCharArray();
      message = new String(decoder.decodeBuffer(message));
      char[] mesg=message.toCharArray();

      int ml=mesg.length;
      int kl=keys.length;
      char[] newmsg=new char[ml];

      for (int i=0; i<ml; i++){
        newmsg[i]=(char)(mesg[i]^keys[i%kl]);
      }
      mesg=null; keys=null;
      return new String(newmsg);
    }
    catch ( Exception e ) {
      return null;
    }  
  }}

gives me:

Encrypted: UBJdXVZUElBBRRFdVRRYWF5YFEFUUw==

Decrypted: a nice cup of milk tea

And this PHP code:

<?php

$input = "a nice cup of milk tea";
$key = "12345";
$encrypted = XOR_encrypt($input, $key);
$decrypted = XOR_decrypt($encrypted, $key);

echo "Encrypted: " . $encrypted . "<br>";
echo "Decrypted: " . $decrypted . "<br>";

function XOR_encrypt($message, $key){
  $ml = strlen($message);
  $kl = strlen($key);
  $newmsg = "";
  
  for ($i = 0; $i < $ml; $i++){
    $newmsg = $newmsg . ($msg[$i] ^ $key[$i % $kl]);
  }
  
  return base64_encode($newmsg);
}

function XOR_decrypt($encrypted_message, $key){
  $msg = base64_decode($encrypted_message);
  $ml = strlen($msg);
  $kl = strlen($key);
  $newmsg = "";
  
  for ($i = 0; $i < $ml; $i++){
    $newmsg = $newmsg . ($msg[$i] ^ $key[$i % $kl]);
  }
  
  return $newmsg;
}

?>

gives me:

Encrypted: MTIzNDUxMjM0NTEyMzQ1MTIzNDUxMg==

Decrypted:

Wonder why both results are different.
I must admit before that PHP is not my cup of tea.

BTW, I use this for a toy project, so high security is not needed.

Answer 1

In your PHP encryption method, you have the following code:

for ($i = 0; $i < $ml; $i++){
  $newmsg = $newmsg . ($msg[$i] ^ $key[$i % $kl]);
}

However, $msg is not defined anywhere. That should be $message.