Existence of universal one-way function

killertoge

11/9/23, 5:13 PM

I have some troubles with this proof from Foundations of Cryptography by Oded Goldreich p.52. Why exactly does the parsing of x to x'x'' take quadratic time in length x'x''? If I have |x'x''|=p(|x'|), and a x of this length. I will try step by step all prefix lengths |x'| in {1, 2, ..., |x|}, till I have p(|x'|)=|x|. So I determine at most p(1), p(2), ... p(|x|). I am not quite sure what to say about the complexity. And if I get an input of the form g(Un), why I cannot instantly request a successful f-inverter to get me the inverse of this. Don't I assume that every attacker knows how g works, say how the description is? (Kerckhoffs principle). Why is the chance dropping? And I do not get why f(desc(M),x) is weakly oney-way in the abstract sense. I mean we just showed it for f(desc(Mg),x).

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Elon Musk

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