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# Questions tagged [collision-resistance]

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

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1answer
405 views

### SNARK-friendly one-way compression functions

I'm looking for a one-way compression function that is secure and efficient within a zk-SNARK circuit. The motivation behind this comes from these considerations: SHA256-compression is highly ...
2answers
556 views

### Partial collisions of hashes, why is this important?

There's a lot of work finding "partial collisions" in hashes, and "Parallel Collision Search with Cryptanalytic Applications" seems to be the go-to paper for this work. I'm trying to understand why ...
1answer
642 views

### Does Composition of compressing Collision Resistant Hash Functions $H^{*}=H_2(H_1(x))$ is Collision Resistant?

I'm trying to solve the following problem: Given two CRHF $H_1:2^{4n}\to2^{2n}$, $H_2:2^{2n}\to 2^n$, construct the following hash function $H^{*}=H_2(H_1(x))$ compressing from $2^{4n}\to 2^n$. We ...
2answers
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### AES_256_ENCRYPT_CTR(key, sha-1(plainText)+plainText) VS AES-GCM, which is more secure? [duplicate]

What if we encrypt sha-1 hash of the plain text, along with the plain text using AES-256 in CTR mode? How much future proof the above method would be in comparison to AES-GCM or any other method ...
1answer
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### Hash Collision Probabilities

Please give help! how can I calculate the probability of collision? I need a mathematical equation for my studying. Assume, I am using SHA256 to hash 100-bits. Thus: SHA256 {100} = 256-bits (hash ...
2answers
291 views

### On a lower bound for the birthday problem

I'm now familiar with a lower bound for the birthday problem as exposed in the theorem A.16 of Katz and Lindell book (alternatively see this webpage). If one denotes by $C(q,N)$ the probability of ...
1answer
145 views

### Is there an information theoretic equivalent of a trap door collision free function?

Warning: Possibly ill-posed question. I'm using the following definition from a recent paper available here. I believe their terminology is slightly different but reproduce my understanding of it ...
1answer
108 views

### What is the smallest last value of sequence of integers from 1, where there is a collision in md5? [duplicate]

Question is just out of interest. If we take md5 hash from all integers from 1 to n, what is the first n, where its md5 collides with some previous md5? Has anyone ever calculated and proved the ...
1answer
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1answer
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### Why do m and m' both hash to H2?

I'm trying to understand the following text: I'm having trouble understanding why $m$ and $m'$ both hash to $H_2$. I tried doing truth tables for $m_1'$ and $m_2'$ given the equations but I don't ...
1answer
331 views

### What does Keccak being “efficiently invertible” mean?

Reading through Wikipedia, I saw this: It has been shown that the Merkle–Damgård construction, as used by SHA-2, is collapsing and, by consequence, quantum collision-resistant, but for the sponge ...
1answer
2k views

### MD5 - Chosen Prefix Collision Attack

Given 2 messages $m_1$ and $m_2$, in a chosen prefix attack, we want to find $s_1$ and $s_2$ such that: $\text{MD5}(m_1 || s_1) = \text{MD5}(m_2 || s_2)$ Are $s_1$ and $s_2$ found by brute force ...
1answer
295 views

### Is there an $n$-bit hash function such that $n$ is equal to the length of input and the collision resistance is close/equal to $2^{n/2}$?

Let $B$ denote a non-empty bitstring of arbitrary length. Then let $n$ denote the length of $B$. The question: does there exist a cryptographic hash function $H$ that outputs a hash $h$ of $B$ such ...
2answers
779 views

2answers
1k views

### Rolling your own crypto

I know this is usually frowned upon, but supposing you were to roll your own encryption cipher (completely on your own or with a small group of friends, with no peer review possible), what could you ...
0answers
49 views

### Hash Function SHA-3 [duplicate]

I would like to discuss the minimum input of hash function to consider strong (e.g Shack128 (SHA-3)). I have a mechanism based on SHA-3, but the input is just 40-bit, some friends told me 40-bit input ...
1answer
172 views

1answer
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### Is there are a metric based on collisions to compare bad hash functions?

Bad hash functions are not so perfect as in the "general collision probability" hypothesis... And a general concept of "collision resistence" not need the constraint of independence between the ...