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.
Questions tagged [hash-function]
254 questions
16
votes
6 answers
How to classify polyominoes by shape
I am trying to find a robust way to classify and distinguish polyominoes . I would like to write a simple algorithm that could identify similar free polyominoes (under translation, rotation, reflection or glide reflection), given a set. Since I am…
Tropilio
- 287
13
votes
3 answers
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've read Bernstein himself has no reasonable…
D. Patrick
- 622
11
votes
0 answers
How to attack universal hash function based on finite-field arithmetic?
As per the Recursive n-gram hashing is pairwise independent, at best paper, I want to use the algorithm described in chapter 6 and 7 (page 7 - 10). The hash works as follows: Define a random function $h_1$ that maps elements in a set $B$ to elements…
Paya
- 111
- 6
8
votes
6 answers
Hide my invoice number
I'm not a mathematician, so please forgive any ignorance. I have a small business - I'm generating invoices incrementally. I'm currently on about invoice number 4000. I guess I don't want my customers knowing how much business I'm doing (i.e. if…
Eamorr
- 225
8
votes
3 answers
Where do hash functions come from?
I have some basic understanding of how hash functions work, however, I have no idea of how mathematicians created them. Were them a byproduct of a non cryptografics related research or were them a result of a desire to find them? Is there some sort…
gjvnq
- 201
7
votes
1 answer
Analysis of a calculation of expected number of collisions in hashing
For a formal problem statement, I quote from the text Introduction to Algorithms by Cormen et. al Suppose we use a hash function $h$ to hash $n$ distinct keys into an array $T$ of length $m$ . Assuming simple uniform hashing, what is the expected…
Abhishek Ghosh
- 835
7
votes
2 answers
What's the difference between a fingerprint and a hash?
My understanding is that both a fingerprint and a hash are functions that take as input some arbitrarily long bitstring, and output a bitstring of a fixed size. The Wikipedia page for Hash Functions says: Hash functions are related to (and often…
6
votes
3 answers
Calculate unique Integer representing a pair of integers
I have a pair of positive integers $(x, y)$, with $(x, y)$ being different from $(y, x)$, and I'd like to calculate an integer "key" representing them in order that for a unique $(x, y)$ there is an unique key and no other pair $(w, z)$ could…
IggY
- 207
6
votes
1 answer
Hash function and one near hard example?
Example: Suppose $H:$ { $1,...,n$ } $\rightarrow $ { $1,..,n$ } be a uniform hash function. for input $x$ , $z$ is equal to number of trailing zero in the right side of $H(x)$ . for $0 \leq c \leq 1$ what is the order of probability $ z \geq c…
Mio Unio
- 79
6
votes
0 answers
Bloom Filter with an interval input
I have been trying to design a variant of a bloom filter that can insert an interval of values at once, as well as query if a certain interval is in the bloom filter. I haven't been able to think of a faster case than the naive method of inserting…
bloom
- 131
6
votes
0 answers
Bloom filter optimization on an interval of inputs
I'v been tackling a problem with bloom filters. I have a basic version working on paper, but I need to be able to put a large interval of numbers into the filter at a given time. Let I be an interval within [0,U] . The problem is to put I into set S…
bloom
- 131
6
votes
2 answers
Finding a minimal perfect hash function for small sets quickly
I'm trying to solve the computer science problem " Minimal perfect hash function " ( MPHF ). I have an algorithm that can generate a MPHF for very large sets in $O(n)$ that only needs 1.54 bits/key, very close to the theoretical limit of 1.44…
Thomas Mueller
- 241
5
votes
2 answers
Toy cryptographic hash function for education purposes?
I'm teaching some high school students about number theory and cryptography, and I'd like a hash function (or ideally, a family of hash functions) that I can use as simple demonstration for cryptographic hash functions. The students have learned…
RichN
- 71
5
votes
2 answers
"Additive" hash function
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 , another function g must exist, having the property g(f(X),f(Y))=f(X||Y) , where ||…
Nya
- 151
5
votes
1 answer
Mathematical notation for Hash Tables
A matrix is nice for modelling arrays, eg const A = [1, 2, 3, 4] const a1 = A[0] const a2 = A[1] const a3 = A[2] const a4 = A[3] can be modelled with $$ A = \begin{bmatrix} 1\\ 2\\ 3\\ 4 \end{bmatrix} $$ $$ a1 = A_1\\ a2 = A_2\\ a3 = A_3\\ a4 = A_4…
Dmytro
- 1,165