Have you ever built a NN model? Have you ever broken a crypto system, even a small one?
You can build and train a model in about 15 lines of pytorch. And you can build and break your own 8 bit xor cipher in about 10 lines of python.
Hacker news is full of software engineers. You are unlikely to find one that hasn't built a model using pytorch these days, and an xor cipher is a common university lab exercise.
For any NN to learn, the function it is approximating must structured enough to admit small set of parameters (i.e., not exponential), otherwise it will take exponentially many nodes to do anything. AES is not differentiable, as are all secure hash and encryption functions. This is a basic test that is used to attack everything.
So you'd get a NN that must be big enough to simply memorize all plaintext, key, output triplets, which is simply a lookup table. With around 2^768 nodes. Good luck.