Look at line 16

main.rs

extern crate rustc_serialize;

use rustc_serialize::hex::{FromHex,ToHex};

/*
   This is the application main
*/
fn main() {
    
    let a = "1c0111001f010100061a024b53535009181c";
    let b = "686974207468652062756c6c277320657965";
    let control = "746865206b696420646f6e277420706c6179";

    println!("a:	{}\nb:	{}\ncontrol:	{}\nperformed: 	{}", a,b,control, xor(a,b).to_hex());
    println!("What about?");
    println!("b:	{}\ncontrol:	{}\na:	{}\nperformed: 	{}", b,control,a, xor(b,control).to_hex());


}


/* 
   This function does an exclusive or operation on two hexadecimal strings
*/
fn xor(a: &str, b: &str) -> Vec<u8> {
   return a.from_hex().unwrap().iter().zip(b.from_hex().unwrap().iter()).map(|(&x,&y)|x^y).collect();

}