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# Questions tagged [collision-resistance]

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

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2answers
757 views

### Can SHA512 and SHA3-512 Make Same Collisions?

Does combining those two different cryptographic hash functions in HMAC, when each hashes the same data separately, then saved together, guarantee zero possibily of a collision simultaneously or is ...
1answer
80 views

### How to prove truncated MD (or chop MD) hash function is collision resistant?

We have a collision resistant hash function (based MD construction) H with 2n bits hash value size. Call chop(H) is a chopping n-bits from H's hash output. How can I prove a chop(H) is collision ...
1answer
33 views

### Breaking merkle damgård construction that uses bitwise and?

I'm preparing for a exam in crypto course, and i'm doing some practice problems. I'm now playing with this problem: ...
2answers
39 views

### Shake256 Infinity Collision

Two diferents inputs can have the same output in $Shake256$ for every output size (for example, $Shake256(input_1, \ell) = Shake256(input_2,\ell)$ for every $\ell$)?
1answer
107 views

### Example of a Hash function which is second pre-image resistant but not collision resistant [duplicate]

We know that a collision resistant hash function is also second pre-image resistant. But the converse is not necessarily true. I am looking for the example of a hash function which is second pre-image ...
3answers
491 views

### What is this AES SBOX triplet property?

While playing around with the AES SBOX, I found out that there are 85 unordered triplets (a, b, c) that have the following characteristics: ...
1answer
106 views

### Are SHA-256 and SHA-512 collision resistant?

This is my first post on this forum, apologies if this post is naive. I want to learn cryptography and I want to start with this question. Context: Designing a TinyUrl system. The user inputs a ...
2answers
220 views

### Use slow hashing to reduce digest size?

I have seen this question on MD5 replacement for 128 bit digests. It is said numerous times that having a 128 bit digest is impossible today because finding a collision would only require $2^{64}$ ...
3answers
108 views

### Using date stamp down to milliseconds / ticks as a salt?

As I understand it, the salt is used to ensure that a hash of two of the same strings results in a different hash. The salt is often stored with the hash, either prepended or as a separate field. As ...
2answers
19k views

### How secure is SHA1? What are the chances of a real exploit?

I read that, in February 2017, a SHA1 collision was calculated for the first time. This, and earlier theoretical proof, means that SHA1 is officially cryptographicaly insecure. But, when using SHA1 in ...
1answer
77 views

### Depth of the SHA-256 collision search knowing partial input and final hashes

So I have a partial input data (string) PART1+UNKNOWN+PART2, length of UNKNOWN is self-describing. I have a bunch of valid ...
1answer
37 views

### Finding multiple smaller collisions equal work as finding a bigger collision?

Problem A: I receive two hash digests $H(x), H(y)$ and the corresponding preimages $(x, y)$. $H$ is a 128-bit cryptographic hash function: $H: \{0,1\}^{*} \longrightarrow \{0, 1\}^{128}$ I need to ...
3answers
316 views

3answers
581 views

### How to prove that finding a cycle in a cryptographic hash function is hard?

I want to show that finding cycles in a cryptographic hash function is hard. My thought: assume there a black box, that given a cryptographic hash function $h$, finds some $x$ and $r$ in polynomial ...
1answer
277 views

1answer
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### Dan Boneh's explanation of why Davies-Meyer requires the final step of XOR with the previous Hash

This is from this video https://www.coursera.org/learn/crypto/lecture/XZt5V/constructing-compression-functions At 2:44, Dan Boneh explains why the XOR is required. This is his explanation m - message ...
0answers
28 views

### Extractability of random oracle in simulation-based proof

I am working on the simulation-based proof, where Random Oracle (RO) is used to extract malicious parties' input. In particular, the RO considered in the proof has a small range (whose size is ...