Is this proof that the universe cannot understand itself? It seems weird that there can be a set of information in the universe that can be hidden from the rest of the universe.
Not entirely. Cryptographic primitives are based on hardness assumptions. For example, we assume discrete log cannot be computed in probabilistic polynomial time when we leverage things like Diffie Hellman. No one has yet proven whether this assumption (and many others like it) is true or false, but so many people way smarter than you or I have tried and not made much headway and so it's safe enough to rely on it.
If someone were to prove one of these assumptions is true, then I suppose the answer to your question is yes, but I wouldn't hold my breath waiting for such a proof :)
> Is this proof that the universe cannot understand itself?
What does “understanding” means when talking about an inanimate thing?
> It seems weird that there can be a set of information in the universe that can be hidden from the rest of the universe.
Why should the rest of the universe “know” anything about other parts of the universe?
Ascribing “understanding” and “knowledge” to the universe sounds questionable from the start, it doesn't seem weird to me that the universe doesn't have these properties.
If someone were to prove one of these assumptions is true, then I suppose the answer to your question is yes, but I wouldn't hold my breath waiting for such a proof :)