# Questions tagged [collision-resistance]

Difficulty of finding two different inputs that hash to the same value

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### Does every 256 bit number have a distinct sha256 result? [duplicate]

If I were some how able to create a table of all 256 bit inputs and outputs of sha256, would each of the inputs have a distinct output?
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### How to create two partly similar plaintexts with same MD5 hash value?

The problem I'd like to solve looks like this: There are two plaintexts which differ in length and letters, but contain a few common strings. The first few words and the last few words are the same, ...
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### How many hash collision will exist where the digest is a pre-image?

This question follows on from the question Circular hash collision where digest is pre-image: Could hash(a) = b, hash(b)=c, then hash(c)=a? The question was answered but the issue of the number of ...
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### How does concatenating diverse hash functions affect collision resistance?

Let's suppose I take 3 different types of hash functions and concatenate them for future safety so that: digest = Hash3( Hash2( Hash1( text ))) Does the birthday attack mean in this case that I must ...
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### Strongest collision resistance test?

An administrator is testing the collision resistance of different hashing algorithms. Which of the following is the strongest collision resistance test? A. Find two identical messages with different ...
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### Simple commitment scheme using secure hash function

Can I create a simple commitment scheme using a secure hash function? If so, is concatenation with a random secret enough to preserve hiding? (i.e. $C = H( random\_string || message)$) Thank you
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### Is it possible to truncate AES output and keep uniqueness (no decryption needed)? [duplicate]

I would like to hash numbers less than 1000000000, so generally they could be stored on 30 bits. The aim is to obtain numbers that are not reversible, so my initial plan was to use SHA256 (with some ...
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### Please explain me why we require $2^m$ & $2^{\frac{m}{2}}$ random messages

Assume that a one-way Hash function is secure and the best way to attack it is by using the brute force attack. It produces an $m$-bit output. Finding a message that hashes to a given hash value would ...
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### collision resistance of a composed hash function

Given a collision-resistant hash function $H(x)$, say SHA256, and I devise another hash function by $H'(x)=\sum^{m}_{1}H(x||i) \mod p$. The summation is defined on finite field of prime order $p$. ...
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### Security issues with computing parallel hashes?

One issue with most hash algorithms like SHA-256 is that it is inherently serial. You can't effectively use SIMD to parallelize a single SHA-256 calculation. However, you can calculate multiple SHA-...
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### Collision resistant hash function implies one-way function

I'm struggling to give a formal proof that $CRH \implies OWF$ using the definition below. Intuitively, I see why a $CRH$ would be "hard to predict" and might be used as a $PRF$, but I'm unable to ...
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### How secure is a hash based signature scheme after signing assuming quantum computers?

Consider a hash based signature scheme that requires taking the $k$-bit hash of an arbitrary length message to be signed (e.g. Lamport one-time signature scheme). My understanding is, assuming that ...
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### Collision resistance of partial SHA-256 hashes XOR'ed

My hashing algorithm computes the SHA-256 for each of 12 input strings and XORs them to get the final hash. Is there a risk of an attacker being able to forge 2 sets of inputs that yield the same ...
As I understood, the GPV signature scheme works as follows: KeyGen($1^n$) : Generate a Lattice with public $A \in Z_q^{n.m}$ and a secret trapdoor $t$. Sign $m$: compute $\vec y = H(m) \in Z_q^n$ ...