Questions tagged [hash-function]
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How many bits are required to sample an almost pairwise independent hash function?
A family of functions $\mathcal{H} = \{ h\colon \{0,1\}^n \to \{0,1\}^m \}$ is said to be $\varepsilon$-almost pairwise independent if, for every distinct $x_1,x_2 \in \{0,1\}^n$ and (not necessarily ...
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Are perceptual hashes connected to audio/video compression?
Without loss of generality, I'll only talk about video, but this should apply to any sort of signal.
A perceptual hash function (WP) maps videos to fingerprints such that each fingerprint's preimage ...
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Reference Request : Accessible reference for Randomised algorithms and Hashing for non-Computer Scientists?
My goal is to understand well a paper like ApproxMC. It discusses the use of Hash functions for Propositional Model Counting. In my understanding what they call hash functions are just random XOR's ...
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Optimal random bits complexity for universal hashing
Let $Q_N:=\{0,1\}^N$ denote the $N$-dimensional Hamming cube. Let $a\in Q^N$ and $X\sim\mathrm{Unif}(Q^M)$ be input and random bits respectively, and function $f$ maps the the joint space to the $P$-...
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"Fair" hash functions
Motivation. When I use a hash function, I would like my pre-images (original values) to a given output (hash) to be evenly distributed as it could be that an uneven distribution could make guessing / ...
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Fibers of hash functions
Let $\{0,1\}^{<\omega}$ denote the collection of finite binary sequences. By a hash function we mean a computable map $$h: \{0,1\}^{<\omega} \to \{0,1\}^n$$ for some fixed $n\in\omega$. Define $\...
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Can hash functions speed up quantum simulation? (Generalizing May and Schlieper's idea) [closed]
To conform with the CS Theory SE crossposting rules, I've created a separate post for dequantizing Shor's algorithm (discussion on the Quantum Computing Stack Exchange was mostly about Shor's ...
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Can a result of (any) hash algorithm contain the hash result itself? [closed]
Suppose you have a file of 240 lines. Any lines, any content.
You then calculate the hash of that file, let's say MD5, and the result is something in the following structure:
...
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Sampling from a family of hash functions, not uniformly at random?
Many algorithms and data structures assume access to a family of hash functions satisfying some nice property (say, $k$-independence or $k$-universality). In these cases, we usually assume that we ...
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Zero Knowledge proofs of knowledge
Is there Zero Knowledge Proof of Knowledge protocol for Hash function? (If h(v)=w) without revealing v to the anyone can we prove that we know 'v')
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Complexity of solving systems of linear equations with hash preimages
Introduction: I'm researching a decision problem that I thought was in NP because there are certificates for its instances that have a polynomial number of elements. However, I realized that there are ...
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Family of functions with properties similar to k-wise independent hash functions
I am looking for a family of functions that has similar properties to a family of $\ell$-wise independent hash functions. The goal is to hash $\ell$ pairwise different bit strings of length $k$ to a ...
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Can a hash preimage be used to amplify BPP probabilities?
Suppose we are given a (univariate) polynomial $P$ of degree $d$, and we wish to determine if $P$ is identically $0$. A standard way to do this is to use a classical PRG to randomly sample a number $...
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What degree of hash function independence is needed for Bloom filters?
In the traditional analysis of Bloom filters, it's assumed that the hash functions are truly random functions, meaning that each hash function distributes each key uniformly and independently of each ...
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LSH Probabilistic guarantees
A family $H$ is $(r,cr,p_1,p_2)$-sensitive if for all $x,y \in \mathbb{R}^d$ we have:
$\lVert x-y\rVert <r\quad \Rightarrow\quad \Pr[h(x)=h(y)] \geq p_1$, and
$\lVert x-y\rVert > cr \quad \...
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Why do k min-hashes, instead of one hash where we find the k minimum elements?
Traditionally if one wants to sketch streams for Jaccard similarity hashing, one finds the minimum element in each of $k$ permutation for comparison purposes, and then takes number_of_collisions / $k$ ...
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What is the maximal load of a "latency-bounded" Cuckoo Hash?
Cuckoo Hashing is a method for storing key-value stores (or just a set of keys) with a constant worst-case lookup time.
They use two hash functions $h_1,h_2:\mathbb K\to [n]$, where $\mathbb K$ is ...
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Hash-containing Binary Tree?
I saw the question somewhere "Binary tree vs hash table, which one is better?"
And then I thought - "Why not both? Why not combine the two and create a binary tree where each node contains a 'number' ...
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Improving Bloom filter - can we distinguish elements of a database using less than 2.33275 bits/element?
While we usually use large e.g. 64 bit hashes, there are many techniques to reduce this size, e.g. for savings in storage and transmission.
Popular Bloom filter instead of marking just 1 hash ...
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Does this pairwise independent random process have expected max load $\sqrt{n}$?
This is an extension to the question about balls into bins: Example of pairwise independent random process with expected max load $\sqrt{n}$ . There the following question is asked and answered in ...
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is Zero knowledge Proof same as commitment schemes? [closed]
I am studying about the zero knowledge proofs and I am looking for a practical (example based) approach to undrestand its process. I have studied the theory a little bit and I find it interesting yet ...
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"Linear" hashing function
Say we have two chunks of data $X$ and $Y$, which may be of different sizes, is there a non-trivial function $hash$, and operation $*$, such that:
$$hash(X+Y) = hash(X) * hash(Y)$$
...where $+$ is ...
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Notion similar to k-wise independence
I want to construct a family of functions $H:\{0,1\}^n \rightarrow \{0,1\}$ with a property that is similar to k-wise independence. Specifically, I want $H$ to satisfy the following property. Let $k$ ...
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Two papers give contradictory bounds on linear probing. How do I resolve the disparity?
I've been reading over two papers recently. The first, "Why Simple Hash Functions Work: Exploiting the Entropy in a Data Stream" proves that, assuming there is sufficient entropy in a data source, ...
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Shoup-style hashing without one-wayness
Let $H$ be an almost universal hash family of functions from $D^2$ to $D$. For any functions $f,g \in H$ define the function $\langle f,g \rangle : D^4 \to D$ by $\langle f,g \rangle(a,b,c,d) \...
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Extended version of the paper "Consistent Hashing and Random Trees" with proofs
I've been reading the following paper:
David Karger, Eric Lehman, Tom Leighton, Rina Panigrahy, Mathew Levine, Daniel Lewin, "Consistent Hashing and Random Trees: Distributed Caching Protocols for ...
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Load factor of a hashtable: Why not resize based on number of actual buckets used? [closed]
From what I read, the load factor of a hashtable is defined as n/N where n=number of items N=Number of buckets in the hash table
Its recommended you increase the size of your hashtable when load ...
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Far point queries in high dimensions
Given a set of points $X\subset R^d$ and a number $r\in R$, create a data structure for queries of the form: "given a point $q\in R^d$ return a point $x\in X$ with $\text{dist}(q,x)\ge r$".
This is ...
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Example of pairwise independent random process with expected max load $\sqrt{n}$
This question was previously posted at https://math.stackexchange.com/questions/1220292/example-of-pairwise-independent-random-process-with-expected-max-load-sqrtn where it has no answers. I now ...
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Sketches, using ideal hash functions
I've been reading about sketches for processing streaming data (the CountMin sketch, the Count sketch, the tug-of-war sketch, FM sketches, etc.). They use hash functions that are required to be 2-...
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What is the intuition behind simhash? [closed]
Why does simhash work? I understand how to implement the hash algorithm, mechanically, from the many articles such as http://matpalm.com/resemblance/simhash/. But is there a simple intuitive ...
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Tuning Parameters of Locality Sensitive Hashing
We have given a set of $n$ binary vectors each of dimension $d$, i.e. a binary matrix of $d*n$. Our goal is to group vectors which are almost similar, $\forall v_i, v_j\in\{0,1\}^d$, we say $v_i$ ...
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Entropy criterion of efficiency for (comparison using hashing)
I understand that hash is effective iff the "domain" size is smaller than the size of the "general set" - set of all possible objects.
E.g., "domain" is the set of valid english phrases with length ...
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Isn't weakly universal hashing even a stronger than truly random? [closed]
So as far as I know the weakly universal hashing is defined as:
for any $x, y \subset U, Pr(h(x) = h(y)) \le \frac{1}{m}$ where m is a smaller number than the cardinality of $U$, and h are chosen ...
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one-way functions vs. secret-coin CRHFs
Is there any paper which can be used to show that there can be no relativizing construction of a secret-coin Collision-Resistant Hash Family from a one-way function and unlike this paper, does not ...
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Ergodic Theory and Hash Functions
I was thinking about the old question regarding the existence of fixed points in hash functions (for instance, if we restrict the domain of MD5 to $S = \{0, 1\}^{128}$, making it a mapping $S \to S$, ...
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Locality Sensitive Hashing - meaning of a block
I'm reading one of the early LSH papers and I'm a little confused by the meaning of a "block". In particular, in the proof of theorem 1 in section 3.2 (p 522), what are the blocks being pointed to? ...
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Almost universal string hashing in $Z_{2^n}$ and sublinear space
Here are two families of hash functions on strings $\vec{x} = \langle x_0 x_1 x_2 \dots x_m \rangle$:
For $p$ prime and $x_i \in \mathbb{Z_p}$, $h^1_{a}(\vec{x}) = \sum a^i x_i \bmod p$ for $a \in \...
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How much independence is required for separate chaining?
If $n$ balls are placed into $n$ bins uniformly at random, the heaviest loaded bin has $O(\lg n/\lg \lg n)$ balls in it with high probability. In "The Power of Simple Tabulation Hashing", Pătraşcu and ...
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What are alternatives to the random oracle model for modelling hash functions?
I was looking for more realistic alternatives to the ROM for describing hash functions in theoretical proofs. I came across the common reference string model (where hash functions can be modeled as ...
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Length Extension Attack with a fixed length message [closed]
It's well known that using a hash function as message authentication is vulnerable to length extension attacks.
ie. H(key+message) is a bad idea. H(message+key), H(key+message+key) have their issues ...
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count number of i such that ( (a*i+b) mod p) mod k == l
How to determine the number of $i$'s as fast as possible such that
$$1\le i \le L$ and $((ai+b)\mod p) \mod k = l$$
where $p$ is a prime number, $1\lt a, b\lt p-1$, and $l \lt k \lt L \lt p$.
This ...
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fast range summable hash functions
I'm finding is there any range summable hash function.
ADD: The hash function I refer to is the one that is typically used in tug-of-war sketch(AMS sketch). Please refer to The space complexity of ...
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Continuity vs Uniformity when designing Hash functions
Reading available literature (yep, including wikipedia), I see that hash functions should have (continuity) and map values that differ very little to similar/same hash codes, in particular for (hash ...
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Bloom filter hashes: more or bigger?
In implementing a Bloom filter, the traditional approach calls for multiple independent hash functions. Kirsch and Mitzenmacher showed that you actually only need two, and can generate the rest as ...
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How did Knuth derive A?
When interpreting keys as natural numbers we can use the following formula.
\begin{equation}
h(k) = \lfloor m (kA\bmod{1}) \rfloor
\end{equation}
What I am having trouble understanding is how we ...
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Why SHA-224 and SHA-256 use different initial values?
Wikipedia - SHA-2 says
SHA-224 is identical to SHA-256, except that:
the initial variable values h0 through h7 are different, and
the output is constructed by omitting h7.
RFC3874 - A ...
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Zero knowledge proof for value of a hash function
Is there a zero knowledge proof which demonstrates that Peggy knows a value v whose hash-function is w?
In my understanding of the general theorems on zero-k there EXISTS such a function if the has-...
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Reusing 5-independent hash functions for linear probing
In hash tables that resolve collisions by linear probing, in order to ensure $O(1)$ expected performance, it is both necessary and sufficient that the hash function be from a 5-independent family. (...
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Separation between existence of crypto primitives
I understand how one can build a crypto primitive from another crypto primitive to some extent. The constructions I know build the later primitive using the former primitive as a black box. My ...
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