According to Ken Thompson&#x27;s lecture at his Turing Award, you can&#x27;t:<p><a href="https:&#x2F;&#x2F;www.ece.cmu.edu&#x2F;~ganger&#x2F;712.fall02&#x2F;papers&#x2F;p761-thompson.pdf" rel="nofollow">https:&#x2F;&#x2F;www.ece.cmu.edu&#x2F;~ganger&#x2F;712.fall02&#x2F;papers&#x2F;p761-thomp...</a><p>Practically speaking, you can verify that it&#x27;s unlikely that there is no backdoor, but it&#x27;d take a fair bit of effort.