# Questions tagged [hash]

A cryptographic hash algorithm is a function which takes a variable size input and produces a fixed size output. The algorithm makes it difficult to find two inputs with the same output or reconstruct the input from the output.

2,955 questions
Filter by
Sorted by
Tagged with
629 views

### How much entropy is lost due to collision?

If entropy is hashed with SHA-256 for example, and the input has exactly 256 entropy bits, how much entropy is reduced after hashing due to collision? Is there any reference that explains how to ...
76 views

### Hash Collision: Weak and Strong Resistance [closed]

On average, against a 128-bit-long key, how many more hash computations would an attacker need to perform to break weak collision resistance compared to breaking strong collision resistance? In other ...
1 vote
29 views

### Privacy-Preserving User Tracking Across Systems with Homomorphic Encryption or hashing

I'm working on a project where we have three different software systems—let's call them A, B, and C. Systems A and B handle user data identified by phone numbers and want to send user actions to ...
50 views

### How to prove that signature hash is wrong without reveal message

Let's say we have Bob, Alice and third party. Bob make message signature hash and upload to third party, then encrypt message with Alice pub key and send it to Alice Alice receive message and decrypt ...
27 views

### How to anonymously poll for information in a small group of people?

A company wants to poll employees about their view of the company (by using a web system, say). They would like to do it anonymously, but they don't want people filling out forms more than once. An ...
• 133
1 vote
50 views

### Is KangarooTwelve hash function suitable for generating very large key material as Shake-256 is?

If I take a large truly random portion of data, I know that I can generate a 2048-bits key with it (assuming the random data has more entropy than the key). I read in this forum that Shake-256 has ...
• 391
40 views

### Secure mapping functions

I have two secret numbers $A$ and $B$. Both are uniformly-distributed 32-bit numbers. I need a deterministic function $f(x)$ such that $f(A) = B$. $f(x)$ must not leak any information about $A$ or $B$....
• 117
92 views

### Is it possible to deduce the input of a hash by running in reverse? [duplicate]

If i understand correctly, hashes run a defined set of operations iteratively until the original data is all hashed. Can you take a hash value, run it backward through the last step (or once, for an ...
118 views

### Do "superfast" keyed hash functions exist?

A common family of requirements for (cryptographic) keyed hash functions is that the function $h(k,-)$ should have good collision resistance for all keys $k$, even if the key $k$ is known to the ...
167 views

### What's the name of the property of ideal cryptographic hash functions that effectively make it a random number generator?

Wikipedia says that, for an ideal cryptographic hash function, "the probability of a particular n-bit output result [...] for a random input string [...] is $2^{-n}$ (as for any good hash), so ...
• 133
70 views

### BLAKE2s finding a hash collision [duplicate]

I want to find a hash collision for Blake2 with 32 bit digest length such that i have 2 messages that produce an identical hash digest. How would you do that? is there another option than just ...
373 views

### SHA3-256 vs SHAKE256_256 in XMSS and SPHINCS

By SHAKE256_256, I mean taking first 256 bits of the output of SHAKE256 i.e. SHAKE256_256(M) = SHAKE256(M,256) What is the motivation of choosing SHAKE256_256 ...
• 153
1 vote
96 views

### Construction of Blake2 and Cha Cha

Recently, I was reading about Blake2B and its properties regarding randomness and security, and its connection to Daniel Bernstein's CHA CHA digest. As a budding cryptographer, I find it doable to ...
35 views

• 143
87 views

### How much of SHA3's internal state can be reached?

After reading that about "37% of the 256-bit outputs" of SHA-256 are unreachable when fed only 256-bit inputs [1] I'm curious & confused. The formula from the proof here considers a ...
• 785
1 vote
63 views

### Is it possible to get the negative point with −x in that version of the Pedersen hash over the BaybyJubJub curve?

The Pedersen hash is a low constraints friendly hash for Zk-Snarks. Unlike many algorithms, the Pedersen hash returns a point P = (x,y) on a curve as a hash. ...
• 153
89 views

### Is keccak256 (and similar hash functions) a suitable KBKDF for 256-bit keys?

Let's temporarily work upon the assumption that proper KBKDF functions do not exist, for the sake of argument. Would keccak256 be a secure choice for a KBKDF that derives 256-bit keys from a 256-bit ...