# Questions tagged [computational-complexity-theory]

A subfield of theoretical computer science one of whose primary goals is to classify and compare the practical difficulty of solving problems about finite combinatorial objects

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### How expensive would running a practical application on full homomorphic encryption be?

This is a multidisciplinary question, hopefully I can stay on topic. It has been published that we can now use (try?) fully homomorphic encryption computation on cipher text inputs. But I'd like to ...
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### show that key recovery is not possible in a computationally secure system

(G, E, D) is a computationally secure encryption scheme over the message space $\{0,1\}^n$. Show that the probability that a PPT adversary can recover the key after seeing the encryption of a random (...
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### Has anyone implemented a public-key encryption scheme using a universal one-way function?

There exists a function $f$ such that if one-way functions exist then $f$ is a one-way function. Such a function is called a universal one-way function. Now the public-key encryption schemes that I’...
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### Complexity of Gaussian Elimination over a Finite Field

I read somewhere that the complexity of solving a Linear $n\times n$ system over a Finite Field $\Bbb F_q$ using Gaussian Elimination is $\mathcal{O}(n^3)$ operations in $\Bbb F_q$. What's the role of ...
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### (updated) Utilizing a non-computable function to create a one-way function

Why can't uncomputable functions be adapted to serve as theoretically perfect one-way functions? This has been bugging me for years, and I've never been able to track down an explanation of why it ...
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### Meaning of “Security can be reduced to a problem”

I'm studying reductions in cryptography and confused about the way people use the word "reduction". My question is almost the same as a past question, but what I want to ask is slightly different. A ...