&gt; Why not? What allows AES to escape such an attack?<p>What attack? A known plaintext attack is just a <i>type</i> of attack. There aren’t any such known attacks against AES currently. <a href="http:&#x2F;&#x2F;crypto.stackexchange.com&#x2F;a&#x2F;10837&#x2F;7264" rel="nofollow">http:&#x2F;&#x2F;crypto.stackexchange.com&#x2F;a&#x2F;10837&#x2F;7264</a> is related.