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by im3w1l
2175 days ago
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> we have a pretty good idea how the collective atoms that make up the gasoline will function. Yes, and that idea is based on theories assuming things are probabilistic. Thus bringing us back to my second paragraph. That falsely assuming things are probabilistic works very well in practice. But it may break down under certain conditions, and there may be loopholes. Edit to add: I think this whole thing is very related to pseudo random number generators and keystretching. Maybe computability theory too. If you have a 1gig file generated from a 128bit seed, then the apparent uncertainty (1gig) is much higher than the actual uncertainty (128bit). But since it's so very hard to undo the prng, it will behave very closely to something with 1gig of actual uncertainty. Edit to add again: A fun thought experiment is someone "encrypting" chemical energy into heat, putting the key in a box, only to later go back and decrypt it back into chemical energy. |
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More than that, since you also need to specify the algorithm used for the prng. Your true entropy is the 128-bit key plus the Kolmogorov complexity (https://en.wikipedia.org/wiki/Kolmogorov_complexity) of the generating algorithm.
This is also a good example of how information-theoretic entropy can change based on our prior knowledge. If we already know the generating algorithm, then the entropy is just the 128-bit key.
> But since it's so very hard to undo the prng, it will behave very closely to something with 1gig of actual uncertainty.
No, not really. A one-time pad with 1Gb of actual uncertainty is not made weaker by disclosing 128 bits of entropy. However, 1Gb of PRNG data is made weaker (broken) by disclosing the 128-bit key if the algorithm is known.
We can practically equate the two because inverting the 128-bit system is just as impossible (absent a quantum computer large/fast enough to take 2^64 operations) within the age of the universe as inverting the 1Gb system.