String XOR Method

Hi,

I'm looking for a method that makes a XOR operation between 2 String with the following signature : String xor(String str, String key); and used like this :

String myStr = "treteterterterterter";
String myKey = "terwb897856304984erzvgtze";

String myCodedStr = xor(myStr,myKey);
String myDecodedStr = xor(myCodedStr, myKey);

Note that myDecodedStr is equals to myStr.

It's quitely URGENT for me, so that's why I give 300 points for the source code.

Thanks