Just brute force basically<p>But there seems to be smarter attacks (ref 21) <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Triple_DES#Security" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Triple_DES#Security</a>