Fair enough. Maybe there is some disagreement between the participants of this thread in what &quot;known-known&quot; means. I would say that without a proof that a known-plaintext attack cannot exist, one cannot say &quot;There is not (a known-plaintext attack).&quot; One could say, however, &quot;I do not know of a known-plaintext attack against AES, however I do not know of a proof that rules one out.&quot;<p>Also, HTTP&#x2F;2 traffic may be encrypted using another scheme (which may be vulnerable to large constant blocks in known locations). I don&#x27;t think HTTP refers or deals at all with encryption. I&#x27;m not sure about HTTP2. My understanding is that they are application protocols only and that message integrity protocols occur at a different layer.