# Questions tagged [hash-function]

For questions about hash functions: functions from a big set to a smaller one such that the same output $f(x_1)=f(x_2)$ for different input $x_1\ne x_2$ is unlikely, especially if $x_2$ differs from $x_1$ by a random error or is crafted by an adversary.

175 questions
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### Can someone offer an intuitive understanding of linear/quadratic probing and double hashing?

I'm reading through Introduction to Algorithms, and I'm having trouble grasping intuitively how linear probing, quadratic probing, and double hashing exactly work. I suspect my confusion lies within ...
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### Birthday Problem applied to collisions

I'm trying to extend the birthday problem to detect collision probability in a hashing scheme. Here is my problem. I use the letters and numbers [A-Z][a-z][0-9] to make a set of keys by randomly ...
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I need a hash function that is easily computable in parallel(think of MapReduce framework), so such hash function must be "additive". I.e. given such function f, ...
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### How to create 2048 random bits from 256 bits?

Would merely repeating the same value 8 times be sufficient ? Or is there a more clever approach for doing this ? The 256 bit values would be generated from SHA256 of files.
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### Difference between universal and k-universal

After reading definitions of universal and k-universal (or k-independent) hash function families, I can't get the difference between them. Also, I couldn't find any examples of hash function families ...
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### probability of repeating values in a hashmap

Suppose you have a hashmap where you store values. The hashmap is of size m and supports chaining. The hash function is simple uniform hashing assumption. I understand that the average length of a ...
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### Universal hashing (bijection) with multiplication

I came across this question while thinking about a CS problem: Given a set $S = [a,b]$ , and a string $x \in S^{n}, x = r_1r_2 \cdots r_n$, under what conditions is $H(x) = r_1 * r_2 * \cdots * r_n$ ...
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### Function for unique hash code

I am interested in finding $F(x,y)$, such that $x$ and $y$ $\in \mathbb Z^+$ and $F(x,y)$ is one to one function i.e., $F(x,y)$ is unique for any unique unordered pairs of $x$ and $y$. Regards, ...
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### Discreet bounding/mapping function with convergence/uniformity

Firstly, I was sent here from cstheory.stackexchange.com's FAQ, please tell me if this too is the wrong board (this board's FAQ indicates that I have to goto stackoverflow ??) This is my first ...
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### Can I reverse any hash algorithms to find a set of the possible orginals?

If I map 1024 bits onto a 16 bit hash (just random numbers for conversation sake), I will have an average of 64 collisions per hash (assuming a good algorithm). I wonder if anyone knows any hash ...
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### Curious Properties of 33

Because my explanation has so many words, I'll start with my question and then you can read the explanation if you need to: The Bernstein Hash method uses the number 33 as a multiplier. From what I'...