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Questions tagged [hash]

Mathematical function that maps arbitrarily-sized data to fixed-size integers, often used as keys in hash tables or to help ensure data integrity

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0answers
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Collisions of a compression function

I tried posting this in the math forum but I didn't get any responses. I was hoping someone could give me some advice for how to approach the following problem. If $n$ is a positive integer, let $...
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1answer
533 views

Proving calculating Minhash

I'm reading about MinHash technique to estimate the similarity between 2 sets: Given set A and B, h is the hash function and $h_\min(S)$ is the minimum hash of set S, i.e. $h_\min(S) = \min(h(s))$ for ...
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4answers
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Why is it best to use a prime number as a mod in a hashing function?

If I have a list of key values from 1 to 100 and I want to organize them in an array of 11 buckets, I've been taught to form a mod function $$ H = k \bmod \ 11$$ Now all the values will be placed ...
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1answer
632 views

Hashing algorithm for millions of variable length strings (URLs)

The goal is to distribute approximately 100 million variable length strings, average length 100 characters, uniformly among 100 million buckets. Perfection not required, just no egregious clumping. ...
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1answer
2k views

How to get expected running time of hash table?

If I have a hash table of 1000 slots, and I have an array of n numbers. I want to check if there are any repeats in the array of n numbers. The best way to do this that I can think of is storing it in ...
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1answer
783 views

Hash function - uniformity / strong universality

I am currently learning how randomised Hashing works. So, you have a class (aka family) $H$ of hash functions, each of which maps the universe $U$ to the hash table $N$. That class is called "...
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2answers
401 views

What is Harrison hashing, its applications in web search engines?

What is Harrison hashing and what are its applications in web searching? Can some one give me some relevant information? Update: I found it here , and is a part of M.Tech syllabus of a friend ...
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2answers
663 views

Collision resistant hash function

A function is $(\varepsilon, t)$-collision resistant if there is no boolean circuit (using "not", "and", "or") of size at most $t$ which outputs a collision with probability at least $\varepsilon$. ...
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1answer
1k views

Why does the Count-Min Sketch require pairwise independent hash functions?

The Count-Min Sketch is an awesome data structure for estimating the frequencies of different elements in a data stream. Intuitively, it works by picking a variety of hash functions, hashing each ...
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5answers
334 views

Is the codomain/range of a hash function always $\mathbb{Z}$ or $\mathbb{N}$?

From Wikipedia A hash function is any algorithm or subroutine that maps large data sets of variable length, called keys, to smaller data sets of a fixed length. For example, a person's name, ...
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2answers
176 views

Function that spreads input

I'd like to know if there is a function $f$ from n-bit numbers to n-bit numbers that has the following characteristics: $f$ should be bijective Both $f$ and $f^{-1}$ should be calculable pretty fast $...
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1answer
302 views

How do the following Hash Functions compare?

Consider the two hash functions used to map IP addresses. $x_i$ represents a octave (or "bit field") of the address. Hash Function 1: $$h_a(x_1, x_2, x_3, x_4) = \sum^{4}_{i=1} a_ix_i \bmod n$$ ...
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1answer
319 views

Modulo hash function and multiples of three

This is a textbook based question. In The Art of Computer Programming Volume 3, Knuth says that for a hash function $h(k) = k \bmod M$, $M$ should not be a multiple of $3$. The explanation given is: ...
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2answers
606 views

Collisions of prefixes of MD5 hashes in some fixed interval

I was wondering, if there is an MD5 hash collision in the UNSIGNED MEDIUMINT Range (0 - 16777215). Sadly, I'm unable to run a script to check this myself, due to Memory (RAM) limitations. The answer ...
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0answers
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Algorithm that hashes a collection of sets following their disjointness relation

I wonder whether there is a simple algorithm to do this work: Say I have a collection of objects $C$, and a binary relation $R: C\times C$ that is auto-reflective ($\forall c\in C: c R c$) , and ...
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1answer
261 views

A hash function with predicted collisions

As far as I know, the more collision-resistant a hash function is, the better. But is there any way to define a hash function with predicted collisions? In other words, a hash function that collides ...
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2answers
709 views

Weak hashing function for memorable IPv6 addresses

IPv6 addresses in the form of 862A:7373:3386:BF1F:8D77:D3D2:220F:D7E0 are much harder to memorize or even transcribe than the 4 octets of IPv4. There have been ...
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1answer
160 views

Is open adressing with prime steps bijective?

Who can help me with this topic: Probing with a step width that is a prime number. I am struggling with this question about defining a hashing function $h(k, i)$ for open addressing on a table of ...
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1answer
343 views

Attack on hash functions that do not satisfy the one-way property

I am revising for a computer security course and I am stuck on one of the past questions. Here is it: Alice ($A$) wants to send a short message $M$ to Bob ($B$) using a shared secret $S_{ab}$ to ...
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2answers
5k views

Could quantum computing eventually be used to make modern day hashing trivial to break?

Simply put, if one were to build a quantum computing device with the power of, say, 20 qubits, could such a computer be used to make any kind of modern hashing algorithm useless? Would it even be ...