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.
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Proof of UOWHF construction from a strongly universal hash family
I am currently trying to rigorously prove Lemma 2.2 of [NY].
More specifically, a UOWHF family can be constructed from a composition of a strongly universal family $G_k = \{g : \{0, 1\}^k \rightarrow \...
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What is the purpose of making salted passwords public?
So I was reading through an article about how passwords are salted and hashed through a cryptographic function here, and found out that hashed passwords, along with the plaintext salt values are ...
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What does the leftover hash lemma guarantee for a specific hash function?
Suppose I sample a matrix $h$ from $\mathbb{Z}_2^{l \times n}$ where each entry in $h$ is $1$ with probability 1/2. Suppose I also have a set $S\subset \{0,1\}^n$, and I define a random variable $X$ ...
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Should hash salt and public key be a part of cryptographic signature?
I'm updating some piece of software I wrote quite some time ago. It is supposed to sign some content. So at the moment I have the following process:
I have a (private, public) keys pair. These can ...
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Signing a file vs. a manifest of cryptographic hashes
I’m interested in the tradeoffs of signing individual files vs. signing a manifest of cryptographic hashes and file names.
Let’s say I do some work that results in a handful of files (10s to hundreds),...
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Recommendations for tools and libraries to aid implementation for a Private Key Generator
I'm currently tasked to implement this cryptographic scheme. But currently struggle to understand these hash functions of the scheme. Can anyone explain and suggest a way or some kind of tool to build ...
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How does linearity work with SWIFFT?
I read that SWIFFT is a linear hash function, but I don't understand what this means. The obvious interpretation is that if you have inputs $X1, X2$ each of which is an array of 16 64-dimensional ...
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Random based on video input, why isn't there some predictability
I just saw this article and many like them before where they use a video of some random movement and a hashing function to make a cryptographic random number generator
but I'm always curious why this ...
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Finding security constraints for different input domains of Ajtai functions
I know that the normal construction for Ajtai hash functions is as follows:
Pick $n, m, q \in \mathbb{Z}^+$ such that $n \log q < m < \frac{q}{2n^4}$ and $q = O(n^c)$ for some $c>0$, and some ...
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Is it hard to find m, R to make RG^H(m||R)=C?
Assuming the generator of one group $\mathbb G$ is $G$. Given an element $C\in \mathbb G$ and a cryptographic hash function $H(\cdot)$, is it hard for one adversary to find a pair of message $m$ and ...
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BLAKE3 for Block and Stream ciphers?
When assuming the following idea for ciphers:
For a block cipher, a 4-round balanced Feistel network where the PRF is BLAKE3 and the key schedule is: input key, input key with every odd bit flipped, ...
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What’s the smallest known sha256 hash that was ever produced?
Basically the same question as this one, except in my case the value to be hashed doesn’t have to be a valid Bitcoin block, but is a bytearray of arbitrary length and content (and that my use case is ...
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Is it possible for a given plaintext and ciphertext to have two different keys? [duplicate]
This has probably been asked before but for a given ciphertext and plaintext pair, is it possible to have two different keys producing said pair? Or there are no collisions in AES, unlike hashing ...
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How would I go about reverse engineering a hash function given input string and generated hash
I have a wireless capture of data and it's 12 bit hash. I am trying to identify the actual function that would have generated the hash data.
I tried all the generic 12 bit CRC polynomials but none of ...
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Adding hashes together
Say I have three 64 byte values that I hash into three sha256 hashes (H1, H2, H3). The data does not contain any secrets and it all public data. I am instead hashing the data for integrity purposes.
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Is this an example of a sponge construction?
I am having difficulties understanding a sponge construction, as I don't really understand whether the long internal state of a sponge construction is compressed in the squeeze phase, or whether bits ...
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What is the fastest stable 128-bit non-cryptographic hash function?
I need a stable 128-bit hash function which is extremely fast since it will be used for generating unique IDs for billions of objects.
It doesn't need to be a cryptographic hash function, nor does it ...
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hashing two inputs with a single encryption
I'm looking at hash function constructions that use ciphers. There are many which are analyzed in this paper: https://www.cs.ucdavis.edu/~rogaway/papers/hash.pdf but all of them assume that only a ...
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Hash Output Distribution for Partly Randomised Input
For a good (unkeyed) hash function, if a part of the input is random, is it fair to assume that the output will also be randomised? More specifically, suppose $H$ has an $n$-bit output, and we write ...
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Public one-way bijection [duplicate]
What methods do we know to construct a function $f:D\to D$
with domain $D=[0,n)\cap\mathbb N$ (thus $n\in\mathbb N$ elements);
demonstrably surjective (thus bijective since $D$ is finite);
with ...
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Name for number of output values a hash function can produce?
Any hash function has fixed output size but it does not mean that all values of output values are ever used. What's the term for the size of output set?
As an aside: Can it be calculated? How do most ...
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Is the composition of a hash function with a block cipher collision resistant?
Assume $H$ is a collision resistant and preimage resistant (unkeyed) hash function and $E(k,y)$ is a block cipher where $k$ is the key.
I am interested into the collision resistance of the composed ...
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Find two hard to reverse functions f and h such that f ∘ h ∘ g = h (f and h injective, no constraints on g)
I am looking from 3 functions $f,g,h$ from $\mathbb N \to \mathbb N$ (they can be bijections, they need to be injective at least), such that:
$$f \circ h \circ g = h $$
and $f$ is hard to reverse ...
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Boss insists on storing SHA2(p) || SHA3(p), claiming it "doubles security"
My friend in the software industry came to me with one of his "dumb boss" war stories. This particular time, his (non-technical but eager to learn) manager came to him and told him to, in ...
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Analyzing Insertion Behavior in a Randomized Hash Table
The following problem of my is from final exam for my online course last year; I couldn't have the time to do it, so I want to check whether my answer is correct;
Q5) Given an (entirely) random hash ...
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Secure time based one time password over SMS
I am designing a one time password system, in which I will send the password to the user over some transport (concretely SMS). Once they receive it they will type it into the mobile app. In this way ...
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Algorithm attack on an hash attack (Python)
Here is an attempt at a Python implementation of what is described in the paper I attached as an image.
The algorithm is too slow or there is something wrong with the code. Any ideas!
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Does the length extension attack apply to KDFs?
Older hash functions like SHA-256 and SHA-512 are vulnerable to the length extension attack, which is problematic in the context of a MAC. There are several ways to prevent this:
Use a newer hash ...
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Differences between two RSA signatures using OpenSSL
I want to sign a file called data.txt and store its signature in data.txt.sig. To create the signature, I want to use an ...
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Grow-only set homomorphic hash function from semigroup?
I have been exploring Bellare and Micciancio's "randomize-then-combine" paradigm for deriving set homomorphic hashing functions. I am particularly interested in grow-only sets, such that ...
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Cryptographic accumulator via function composition
I am looking for an alternative to RSA accumulators, and I am wondering if the following option based on function composition might fit the bill. It seems like an obvious tweak on RSA accumulators, ...
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Split a private key into shares and sign successively or separately
Assume I have a private key, priv_k, a public key pub_key and a message, msg, along with its ...
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Security of this MAC scheme
I'm studying for a cryptography exam, I have this question from a past exam:
Consider the MAC with key $k$, based on a block cipher $E_{(k)}$ with block size $n$, and a collision-resistant hash ...
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Random oracle vs implementations like hash function
In this answer, it is stated
It has actually been shown (by Canetti, Goldreich and Halevi) that
random oracles cannot exist "in all generality" in the following
sense: it is possible to ...
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Is the XOR-combiner of independent keyed hash-functions collision resistant?
Assume there are two keyed hash-functions $H_1(k_1, m)$ and $H_2(k_2, m)$, with $k_1$ and $k_2$ being independently randomly sampled public keys.
The XOR-combiner is defined as $C_\oplus^{H_1, H_2}:=...
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What is the advantage of using hash function families instead of a single hash function?
My guess would be that families are more secure. In which way though?
I have seen claims that hash function families can be collision resistant while single hash functions can not be. Is this true? ...
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Citation to original paper by Davies-Meyer on one way compression functions
I see a lot of references to the Davies-Meyer construction for one-way compression functions.
But I can't find any citation to the original paper.
Does anyone have it?
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How good is blake3 compared to a random oracle?
How good is blake3 for generating pseudo-random bitstrings in comparison to a random oracle?
Let's say we generated an arbitrarily long pseudo-random bitstring by concatenating blake3 hashes together ...
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Hashing to the target group of bilinear pairing
Assuming we have fixed pairing friendly elliptic curve groups $G_1$, $G_2$ and $G_T$ where for $a \in G_1$ and $b \in G_T$ it holds $e(a,b) \in G_T$.
Let's put some more context and we are working in ...
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Long term Stream Cipher cipher text with MAC storage
Let's say I have x bytes of data that needs to be encrypted with Stream Ciphers such as AES256-CTR, ChaCha20, Salsa20, XChaCha20, XSalsa20.
I would like to ask, since these ciphers typically requires ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 $B$....
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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 ...
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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 ...
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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 ...
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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 ...
