# All Questions

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### Building an Adversary for a PRF game

Here is the game: How can I make an O(k^2)-time adversary making only one query to its Fn oracle and achieving advantage = 1 - 1/(p-1) Here is my idea so far: query 2^{-1}, which when it goes thorugh ...
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### Bug Bounty for a reversed Hash

this is just a general question, Is there is a bug bounty from the NSA or anyone else for reversing a SHA HASH, specifically SHA-256?
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### Prove: If there exist strong OWFs then there exist weak OWFs that aren't strong

Please help me to understand the proof of the following claim: Assume there exist strong OWFs, then there exist functions that are weak $\frac{2}{3}$-one-way functions, but not strong one-way ones ...
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### hiding bits inside random bits, is this some sort of encryption?

Let's say that I uniformly sample a 1000 bits randomly. Then, I hide a secret of 10 bits on those 1000 bits, randomly. That is, I pick each of the 10 bits and randomly replace them inside the 1000 ...
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### Where can I find good practice questions for proofs by reduction?

I already have the Katz-Lindell textbook, but I also want some additional practice problems for security reductions for stuff like PRFs, MACs, digital signatures, private and public key schemes, and ...
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### Is SHA1 break significant for an algorithm intended to be Proof-Of-Work?

Let's say I'm modifying the Scrypt hash function (https://github.com/Tarsnap/scrypt/blob/master/lib/crypto/crypto_scrypt-ref.c) and that all I want to do is replace SHA256 with SHA1 in the code to ...
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### Is it possible to have a shared secret without any party knowing all the parts?

I believe with Shamir’s Secret Sharing Scheme, I can create an n-part secret and distribute each of those parts to n parties. ...
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### Can you identify these cryptographic algorithmic symbols?

I am mostly self taught and have limited knowledge of the symbology in the image below. It is a diagram of a sub block the RIPEMD-160 algorithm: Are such symbols standardized? Is there a good ...
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### Is this kind of mutual Authentication safe?

The following is a real-world problem. In a standardized protocol clients can connect to a server using mutual 4-pass authentication on an otherwise unsecured TCP channel: pass-1: Client send random ...
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### How to have a hash function that maps any binary string of size n to binary string of size n?

I am implementing certificateless cryptography from this research paper in python language. Essentially, I want to have the following hash function mapping. This hash function is mentioned in the ...