It's an interesting thought experiment, but it feels a little like trying to come up with the best defense against alien invaders. We're already talking about attackers able to craft cryptographic weaknesses decades of peer review can't discover or explain. Trying to figure out how to usefully constrain their algorithm design choices does not seem like a winning strategy.

The bitcoin block hash thing is interesting, but if you're talking about an attacker with that kind of unknown but sophisticated capability, how do you know it actually thwarts their plans? Maybe all they need is any large number with high entropy or maybe the leading zeros characteristic of bitcoin block hashes is actually key to their attack? Once you imbue your adversary with unknown powers, it's by definition difficult to know what helps or hurts them.

heh. well, could drop the leading zeros :)

But, yeah, magic powers, sure, anything goes. I was just thinking there must be something more reliable than NYT headlines.

It's way harder to fake physical measurements (like weather, solar activity, etc) published by international bodies, You could maybeeee influence the least significant digit but even this would be hard without cooking up experimental data.

Maybe get physical measurements, stock exchange data, newspaper headlines, and bitcoin blocks, all in 6 months in the future, and XOR all of them.