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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Find the Algorithm to a Series of Hashes [closed]

I need to find the algorithm that generates this sequence of hashes: ...
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A SHA verifier in the CNF format

Can someone help tell how to generate a 3-CNF verifier for SHA-256 that: outputs 1 if message/input's calculated SHA-256 value matches the pre-provided hash Otherwise outputs 0. Given that the ...
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45 views

Does SHA384 make sense with HMAC-SHA256?

In the sense of security level (as defined, for example, by Ferguson and Schneier in the book Practical Cryptography), does it make sense to use SHA384 with HMAC-SHA256 in the general settings. By ...
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How to change any symmetric algorithm to obtain hash of key and hash of data from encrypted output? [closed]

I want to know how I can change any symmetric algorithm like AES to obtain the hash of the key and the hash of the input from the encrypted output? How can I change any asymmetric algorithm to get the ...
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HMAC vs hashing (data + pepper) [duplicate]

Is there a difference between HMAC and hashing (data + pepper) or both of them are equally secure ?
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Hidden message in photo [closed]

png with hidden message inside, but i cannot decrypt (understand) the message, do you have any suggestions? The code: h5BA68F35I_%3E%3B%3BG3gdc%3E%3EFF9g5deA82hhh%3F%3Ea%3B22gdh%3Ee%3B%3B%6025%...
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1answer
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Should I protect the salt before storing it in a database or use a pepper (secret salt) instead?

If I protected the salt or used a pepper (secret salt) and an attacker got access to the database he can't do a rainbow table attack on a targeted user (a famous or important person). Should I use a ...
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40 views

Is it possible to have a hash in UUID form that ends with 16 characters instead of 12?

You may know how sometimes a hash in a URL may be in UUID format, which consists of groups of hex values separated by hyphens. In UUID format, I have come to learn that this hash takes the form: 8-4-4-...
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Many near collisions but no full collision

I read this question: Cracking $f(x) = Cx \oplus Dx$ Asking about finding collisions in a simple 64 bit hash, and I thought I will give it a go myself just for fun. I quickly wrote code to find ...
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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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1answer
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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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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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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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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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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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459 views

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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40 views

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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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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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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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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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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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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126 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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791 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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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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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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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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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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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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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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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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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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What are the security flaws of SHA? [closed]

I have been researching SHA algorithms extensively, specifically SHA1, SHA2-256, SHA2-512, SHA3-256, and SHA3-512, and have found many instances of successful collision attacks as well as methods. In ...
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How to unhash sha256? Alternatives to brute force?

I know it's almost impossible to do, SHA256 is a one-way function that can't be easily reversed, just like there are operations that have no reverse, take: $f(x) = x+5$ , it's easy to see that if you ...
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76 views

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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How does password_verify() function gets the salt from the password stored in DB?

I am creating a simple Sign up and Sign in form using PHP. At the sign up, I create hash using password_hash() function and then store it in the DB. At the time of Sign in, initially what I did was ...
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1answer
151 views

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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In sha256, is it possible to use less information than the full preimage to prove that the prefix of the preimage is a certain string

Alice split a long string P into two segments A and B. A is relatively short and B is long. H = sha256(A + B) Bob does not know P, but knows H. Is it possible for ...
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Does my SHA-256 TableSalt algo give away the seed salt?

The Setup I have a table of values for which I need to compute a salted hash for each table-cell value. Furthermore, I need the salt for each table cell to be unique and unpredictable. (I can explain ...
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Can SHA512 and SHA3-512 Make Same Collisions?

Does combining those two different cryptographic hash functions in HMAC, when each hashes the same data separately, then saved together, guarantee zero possibily of a collision simultaneously or is ...
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1answer
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is it efficient if blockchain uses double Hash algorithms $H_1$ and $H_2$?

I wonder is it efficient to use less Target condition and double hash algorithms with different target (or the same target with different Hash algorithms) and one nonce in a Block. Example Target 1 ...
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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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Confused about encapsulation using different types of hash functions

I'm reading Improved Efficiency for CCA-Secure Cryptosystems Built Using Identity-Based Encryption. In Section 4 there is a description of encapsulation schemes that says We suggest an encapsulation ...
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Expected Hamming distance of $a+b$ and $(a \oplus b) \oplus ((a \land b) \ll 1)$

Motivation. In their paper about the cryptographic scheme NORX, the authors use a fast approximation of + by bitwise operations (taking fewer CPU cycles than proper addition) using the formula $$a+b \;...
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I'm having trouble understanding this [duplicate]

Let $x=(x_1,x_2,...x_n)∈\{0,1\}^n$ for $n∈\mathbb N$. Prove that if one-way functions (OWFs) exist, then there exists a one-way function f such that for every bit $i∈[1, n]$ there exists an algorithm $...
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Breaking merkle damgård construction that uses bitwise and?

I'm preparing for a exam in crypto course, and i'm doing some practice problems. I'm now playing with this problem: ...

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