# Questions tagged [preimage-resistance]

Difficulty of finding an input string that hashes to a given value

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### Determine if a Hash function is pre-image resistant and collision free

I'm so confused by this kind of exercise. We have that $n = p * q$, where $p$ and $q$ are prime numbers. Let's examine this hash function: $h(x) = x^2 \mod n$. Determine if the hash function is pre-...
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### Why we need DSPR or Eq. 14 for the proof of SPHNICS+?

The paper says that We show that preimage resistance (PRE) follows tightly from the conjunction of second-preimage resistance (SPR) and decisional second-preimage resistance (DSPR). As I understand ...
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### Approximate size of image of SHA512

Let $s: \{0,1\}^* \to \{0,1\}^{512}$ be the SHA512 hash (where $\{0,1\}^*$ is the countable set of all finite $\{0,1\}$ strings. Is it known whether $|\text{im}(s)|/2^{512} \geq 0.5$? If yes, what is ...
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### Potential weaknesses when combining hash functions?

For consistency's sake, M is the message, H1 and H2 are separate hash functions. I've heard that concatenation or XORing hash outputs together do not provide improved security against preimage and ...
1 vote
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### Could multicollisions be used to mine large amounts of cryptocurrency?

I'm reading about hash functions at the moment, and in the book I'm reading there's a section on multicollisions. Specifically, using a 2-collision to find $2^N$ collisions in $N2^N$ time. If, ...
1 vote
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### "Reversing" SHA256 [duplicate]

Let's say I give you the sha256 hash of my password, which I'll call X. Now, the sha256 algorithm is a one-way function, meaning you can give it some input and get an output, but you can't get the ...
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### Is it possible to reverse the final rounds of SHA-256

I've seen a lot of preimage and collision attacks on SHA-256 that target the first few rounds. So far, the best attacks break preimage resistance for the first 52 rounds out of 64 rounds. However, I'...
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### Why would this algorithm be vulnerable to a preimage attack?

If I created this algorithm: Break the message $M$ up into $n$ blocks $m_1,\ldots,m_n$ of 512 bits each. Compute the hash by alternating AND and OR operations on the blocks. More specifically: The ...
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### For SHA3-512, SHA512, and Whirlpool, which algorithm has least probability for collision and preimage collision?

For comparing these 3 hash functions SHA3-512, SHA512, and Whirlpool. Which one is strongest against collision and preimage attacks. Are they fundamentally the same because of the same size output? ...
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### Does double hashing increase resistant against first preimage attacks?

Let's take Bitcoin as an example. Bitcoin uses SHA256, which can be vulnerable to collision and preimage attacks - although this is extremely unlikely to happen in the near-future. However, let's ...
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### "official" guidelines about the minimum length of a truncated hash

I am looking for some reference documentation suggesting a minimum reasonable length for a truncated hash (specifically, a truncated SHA-256 hash) to ensure preimage resistance. Obviously, truncating ...
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### How safe is my method

I'm building a website. I have an API which takes 2 parameters: delete_user(user_id, hash). And there is method to evaluate hash using SHA512: ...
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### Good pre-image resistance value for hash visualization

I want to do "hash visualization", i.e. derive a human-meaningful information from a hash, like a phrase or an avatar. But the current techniques usually don't use many bits, for example tripphrases ...
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### Pre-Image Resistance of repeated, patterned SHA2-256 digests

Suppose $H = \operatorname{SHA2-256}$. Let $H_1 = H(\text{“Alpha1”})$. Let $H_2 = H(\text{“Alpha2”})$. … Let $H_N = H(\text{“AlphaN”})$. So all these digests are based off a common pre-image post-...
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### Why might SHA-384 throughput be lower than SHA-512 throughput in hashcat and more secure?

I found a hashcat benchmark results in the internet: hashcat results: SHA-384 is 17065.4 MH/s SHA-512 is 17280.3 MH/s Why does SHA-512 take less time? SHA-512 is longer and I thought it therefore ...
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