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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Speeding up XMSS

To compute the XMSS Tree root, one needs to compute all the 2^h keys and hash them together. The higher the height of the tree, the more keys there are and the longer the KeyGen computation. The ...
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Using hash of data as proof of integrity and preventing collision

Rather than storing user data when interacting with an app, I am storing the SHA3-256 of the data. This is because data storage in this particular environment is very limited. The data can be several ...
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Cracking $f(x) = Cx \oplus Dx$

A program I reverse engineered is using $f(x) = Cx \oplus Dx$ where C = 0x20ef138e415 and D = 0xd3eafc3af14600 as a hash ...
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PRNG For RSA (ANSI_X9.31)

I have a query please , I want to know how to generate random numbers using ANSI_X9.31 algorithm for RSA Algorithm please . Thank u
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Help in understanding exactly how lattices are used as one-way functions for hashing

In my long-distance cryptography course, an assignment covers lattice-based cryptography. It is hard, and I am lost. There is no one to help me. Thus far, I have understood that: Lattices are a ...
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Remote Attestation: when to use Checksum and when to use a Cryptographic Hash function?

In computer security applications, to check the integrity of a specific data/program binary, a cryptographic hash function is normally deployed to generate a digest and compare it with a reference ...
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Finding $k$ strings $M_i$ such the XOR of the $k$ hashes $H(i,M_i)$ is zero

Let $k\ge2$ be a moderate given constant, and $H:[0,k)\times\{0,1\}^*\to\{0,1\}^b$ be a $b$-bit given hash function assimilated to a random oracle. For example $H(i,M)=\operatorname{SHAKE256}((\...
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Preimage attack on sum of two Hash functions modulo 2

If a hash function $H$ is defined as $H(x_1,x_2) = H_1(x_1) \oplus H_2(x_2)$ for two n bit good hash functions $H_1$ and $H_2$ then how can we construct a preimage attack on $H$ that is of $O(2^\frac{...
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MD5 Collision Attack Explained

In one of my assignments, I came across this: Due to MD5’s length-extension behavior, we can append any suffix to both messages and know that the longer messages will also collide. This lets us ...
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Collision attacks on digital signatures

After reading this document about MD5 collision attacks, I still don't understand how collisions can make digital signatures insecure. In the paper, the researchers created two files with the same ...
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How is a group element converted into a key?

I've only just started research on cryptography so I apologize if this is a basic question or I'm getting terms confused. I'm researching braid group cryptography and currently looking at the Anshel-...
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Is SHA-1 still practically secure under specific scenarios?

It is conjectured that SHA-1 has been broken from the "research" perspective, but not in the real world; that is, there exists an algebraic attack that explores weaknesses on its algebraic ...
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Is there an efficient algorithm that allows to construct a cryptographically secure $n$-bit hash function based on two unkeyed $n$-bit permutations?

Let $f(x)$ and $g(x)$ denote two independent, “ideal”, unkeyed, public $n$-bit permutations (two publicly known bijective functions that produce $n$-bit outputs from $n$-bit inputs), where $n$ is an ...
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Can someone please explain the “secret” and the “data” in the MD5 hashing algorithm?

I've been studying the MD5 hashing algorithm, and there is something that I just don't understand yet. They say that the server holds some sort or "secret" and that it appends some sort of &...
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What are the algorithms used in Facebook's Diem algorithm?

Facebook plan a new cryptocurrency release called Diem. What algorithms are used? What output size is used for the hash function?
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Hash function and operation commuting over composition

Is there a hash function $H$ and operation $\otimes$, which fulfill the following property? $$ H(A) \otimes H(B) = H(A \otimes B) $$ $A$ and $B$ are two byte blocks of identical length, if necessary ...
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Expandable hash function

I have been studying a cryptosystem using Mersenne primes. More specifically, this paper. I have implemented this cryptosystem in Python, but I am missing the key encapsulation system. On page 12, ...
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Examples of post-quantum hash functions

We already know many examples of post-quantum cryptography for asymmetric, symmetric and digital signature algorithms, but is there any risk for hash functions to be attacked with quantum computers ...
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Why do we use hex output for hash functions?

Why do we use hex representation as default for the output of a hash function's result? For example, the SHA-256 hash function: the output of SHA-256 in hex representation uses 64 characters, while ...
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Are my calculations about WOTS parameters correct?

I'm reading the WOTS+ paper, but I'm having some trouble with its notation and specially the involved units. For example, under my interpretation, the parameters ...
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194 views

CCA-Security Proof of a Particular Scheme

Suppose we have a scheme that works so: $\mathcal{P}_k =:\{P_k\colon \{0,1\}^{2n} \to \{0,1\}^{2n} \}$ is a strong PRP family. Encryption: $\operatorname{Enc}(k,m)=P_k(m\mathbin\Vert r)$, where $\Vert$...
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HKDF Bit Security

I've always understood the bit security of hash functions to be related to their output size (eg. collision resistance). However, I recently came across a table from a Wickr blog post that lists HKDF-...
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How to compose multiple values to MAC authenticate?

If the data I want to authenticate consists of multiple values and I compute a MAC simply concatenating the values, an adversary can "shift" characters within those values without ...
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Making WOTS+ public keys shorter

In WOTS+ — as described in section 3 of RFC 8391 — public keys, private keys and signatures all consist of $len$ strings with $n$ bytes each, where $len, n \in \mathbb{N}$. Is it safe to use the hash ...
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What are the properties of a hash function?

I have created a hash function. If I am asked whether it conforms to the definition of a hash function, I only know that it should have a fixed-size output. I use multiplication and adding of every ...
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Is there a feasible preimage attack for any hash function (no matter how deprecated) today?

Has there ever been a hash function that was actually used in the field, no matter how long ago, for which there is now a feasible preimage attack? All hashes that are nowadays considered 'broken' (...
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Finding second-preimage to this use of weak hash

$h'(x) := h(a_1 \parallel x \parallel b_1) \parallel h(a_2 \parallel x \parallel b_2) \parallel h(a_3 \parallel x \parallel b_3) \parallel \dots \parallel h(a_k \parallel x \parallel b_k)$ $a_i$ and $...
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1answer
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W-OTS+ one-wayness property

I am reading the "W-OTS⁺ – Shorter Signatures for Hash-Based Signature Schemes," by Andreas Hülsing, and I am stuck in understanding the success probability of an adversary, $\mathcal A$, against the ...
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Why did the NSA create SHA?

New to cryptography, I'm trying to learn the program Veracrypt, and I'm now trying to understand the history of hash functions and how it applies to Veracrypt. So this is what I understand so far, the ...
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1answer
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Creating a stronger cryptographic hash given a cryptographic hash

I need a cryptographic hash function that will hopefully be strong even in 50 years. Performance is not an issue. Calculating and verifying can take a huge amount of time if needed. The size of the ...
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If the source code of SHA256 hashing algorithm is available in public, why can't it be hacked? [duplicate]

If the SHA256 algorithm is public, why can't attackers use it to create more collisions rendering the algorithm useless?
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Finding the cleartext password given its MD5

Given powerful GPU and PC hardware, is it realistic to recover a password in a few hours given a cleartext's MD5? Max chars are 95, and the maximum length of the password is 15 characters.
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Fast crytographically secure Pseudo-Random number generator in software

What are the methods for generating pseudo-random numbers in software? I have seen methods where people use SHA implementations from openssl to hash a random message as source of entropy, or using AES ...
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Does matrix multiplication of hash digests admit manipulation of the result?

Take a sequence of byte buffers, hash each of them, interpret the hash digests as square matrices with 8-bit unsigned int elements, and (matrix) multiply them in order. Define the final matrix to be ...
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1answer
125 views

Is NOTS a valid one time signature scheme?

I've just learn about NOTS, a quantum-resistant signature scheme based on hash functions that claims to have much shorter signature and key sizes. Is this signature scheme known to be secure? From ...
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2answers
781 views

Cons for stream ciphers that are based on hash functions

In an answer of here someone mentions: if you have a hash-function-with-oracle-powers, then it is rather easy to generate a pseudo random stream from a secret key, by hashing K||n where K is the ...
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What hash structure is Facebook Diem using?

Crypto currencies use fixed values in some positions in the resulting hash, like a fixed amount of initial zeros. What fixed positions and fixed values are Facebook Diem using?
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1answer
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Understanding the HAIFA (hash iterative framework) structure

Unfortunately, this structure doesn't even have a full Wikipedia on it. I'm struggling to understand it. There are no Youtube videos, Lectures, or any educational video on it. I want to understand how ...
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Looking at hash output – is Base64 encoding in any way better than HEX encoding?

I was wondering why most "normal/unsafe" crypto hashes like SHA-256, SHA-512, Whirlpool, RipeMD-160, MD5, etc. are HEX encoded. But most "secure" crypto hashes (KDF' ) like ...
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What vulnerabilities does the LFSR filter generator have?

As the title suggests, I wonder what kinds of attacks there are in the LFSR filter generator. The most representative attack is the fast correlation attack and inversion attack. I wonder what other ...
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Algorithm to validate 1 of N inputs is part of output hash

Is there an algorithm that allows proofing that an input x1 was used as 1 out of N inputs to create an output hash y, without ...
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425 views

Hash Function Properties

What I am trying to understand is shown in all three properties of a secure hash function, I will focus on Preimage attack resistance. Preimage resistance: given a hash h, it's difficult to find m s.t....
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Keyed Hash Functions [duplicate]

What are keyed hash functions? Why are they needed? I have never used a hash function which specifies the key so not getting the significance. The key need not be secret. Why is it so?
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Is there a crytographic scheme for “ciphertext consistency verification”?

I a problem that essentially boils down to the following: There is raw data, D, encrypted with key K (call its encrypted form <...
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1answer
69 views

Two Different Ciphers with Same MD5

I was wondering if someone could help explain md5 collision abit better. I found this resource: https://www.mscs.dal.ca/~selinger/md5collision/ where they provided an example of where two cipher texts ...
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56 views

Security of Hash Functions

Given a Hash Function H, how are the properties such as collision resistance, target collision resistance, one wayness, and non-malleability proved? I have read about hash function and stating that it ...
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Complexity of Hash mining/signing

While reading about mining in crypto currency, I found that it requires some leading bits of a hash function output to be 0. This boils down to preimage resistance of the hash function, hence done ...
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Validating a partial message from a hash

Let's say I have 3 items (A, B, C). Is there some sort of hash algorithm such that if I send (A, B, C) to another person, they ...
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14k views

What are the odds of collisions for a hash function with 256-bit output?

There are some related questions on the net but I did not understand their solutions. I am reading in a textbook about methods of finding a collision. It states to consider a collision for a hash ...
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Can there be an injective function that maps a large set of integers to a smaller set while being “collision-aware”

Consider two sets: The "big set" contains all integers between $0$ and $2^{160}$ exactly once. The "small set" contains all integers between $0$ and $2^{32}$ exactly once. Given ...

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