And even then, we'd need to invent a cryptosystem whose hardness depends on an NP-complete problem, and be able to reliably find hard instance of that problem.

And even then, we'd need to invent a cryptosystem whose hardness depends on an NP-complete problem, and be able to reliably find hard instance of that problem. There are interesting attempts at that which have failed e.g. the Knapsack cryptosystem: https://en.wikipedia.org/wiki/Merkle%E2%80%93Hellman_knapsack_cryptosystem https://en.wikipedia.org/wiki/Merkle%E2%80%93Hellman_knapsac...