It&#x27;s &quot;fair enough&quot; because it gets the important parts right of having a large number of states.  Just like your coin flip would get the important parts right if it was used in specific ways.<p>A coin in the real world isn&#x27;t fair, because it could land on its side.  But it&#x27;s fair <i>enough</i>.<p>Statistical sampling doesn&#x27;t give you guaranteed-accurate results.  But the biases cancel out across the metrics you&#x27;re measuring, so it&#x27;s good enough.<p>I didn&#x27;t ignore your jab at the NSA, but it&#x27;s pretty weak.  The backdoored CSPRNG doesn&#x27;t give numbers that are worse than any non-backdoored CSPRNG.  Depending on your perspective, it can give you uniformly any number, or it can give you only a single number, and the same is true of good algorithms too.