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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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11 views

AEGIS/MORUS as a general purpose hash function

Can AEGIS/MORUS, ignoring its output except the tag and with a fixed key and IV, be used as a general purpose cryptographic hash function?
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Diffie-Hellman key exchange in four parties

I understand the concept of 2 and 3 parties Here is the code of 3 parties ...
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2answers
133 views

If a new hash function were made that simply truncated sha-256 to the first N bits, how much insight would it provide into sha-256?

Clearly it would provide perfect insight if all 256 bits were used. What about if 255 were used? Would the general behavior and properties of "sha-255" be expected to be close to sha-256? What about "...
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Why not use chacha derivatives (BLAKE, rumba) to make an [H]MAC for use with chacha? Why use poly1305?

Why not use chacha derivatives (BLAKE, rumba) to make an [H]MAC for use with chacha? Why use poly1305? This question is especially interesting considering... "The security of Poly1305[...] is very ...
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Why is the core ChaCha primitive not good for use in a CRCF? Why create BLAKE?

Why is the core ChaCha primitive not good for use in a collision-resistant compression function (crypto hash)? Why go through the trouble to create BLAKE? What's wrong with using the core ChaCha ...
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Message Length Restriction in EIA3

EIA3 (EPS Integirty Algorithm) produces a 32 bit MAC value. The message length for this is restricted to 20000 bits. Quoting the document: The integrity algorithm (128-EIA3) computes a 32-bit ...
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Given a hash function; assuming domain % codomain = 0 and uniform collision distribution; how is entropy lost by collisions (not output truncation)?

Assuming our domain and codomain both have 4 elements, the uniform distribution of inputs to outputs means the function is injective. It is widely agreed that randomly selecting a domain element ...
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1answer
34 views

Merkle–Damgård transformation example

I m looking at this Example of Merkle–Damgård I have a similar question about this topic. I have hash function maps 256b blocks into 128b blocks, how many rounds are required for hashing a 140KB ...
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Entropy preservation through cryptographic hash function

Background First, while studying MinEntropy a bit, I came across an NIST paper, "DRAFT SP 800-90B (second draft)," which suggests "twice" the entropy of the underlying block of a cryptographic hash ...
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1answer
47 views

Zero Message Length HASH

What does it mean by a HASH of a message with zero length or rather why is it required? What could be a possible scenario where this is used? Also note that, for a given HASHing algorithm, the hash ...
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How do you find hashes? [closed]

How do you find hashes ?im having a hard time figuring out how to find hashes ?
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1answer
54 views

What's the proper way of fitting hash digest to encryption scheme?

I would like to know what is the proper way of fitting the hash digest to the prime in which the encryption scheme operates. regardless if the bits of the hash digest is larger or smaller than the ...
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Is there any vulnerbility on the following algorithm? [closed]

Let SHA3_512(message) -> digest is a function of SHA3 512 bits. And operator + is for string connections. I am going to use ...
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2answers
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Why might SHA-384 throughput be lower than SHA-512 throughput in hashcat and more secure?

I found a hashcat benchmark results in the internet: hashcat results: SHA-384 is 17065.4 MH/s SHA-512 is 17280.3 MH/s Why does SHA-512 take less time? SHA-512 is longer and I thought it therefore ...
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Can I prove that hash of modified preimage is valid

Assume that hash(X) == Y Alice knows both X and Y Bob only knows Y Alice generates a random nonce N and shares it with Bob. Alice calculates H = hash(X⊕N) and shares H with Bob. Can Alice prove to ...
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Is there a reason to use multiple hashing algorithms in a single system?

I came across an authentication system Here that uses multiple hashing algorithms to hash data in different stages of the authentication. My question is what's the rationale behind this? If a hashing ...
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How to encrypt small pieces of data (2 - 4 bytes) within Beacon advertising packet?

I'm developing a medical device that operates under extreme low-power constraints and transmits data with BLE, where every unnecessary millisecond of air time matters. I am developing a Beacon ...
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Is finding a three way hash collision infeasible [duplicate]

Is there an equivalent to the birthday paradox for more than 2 messages. Solving Hash(x) = 0 takes $2^{bits}$ steps on average Solving ...
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1answer
40 views

Input Hash Size of ECDSA Signature over Curve secp521r1

For encryption authentication, I am using ECDSA signatures over the curve secp521r1. There is a hash function parameter, and as the curve is 521-bit, the hash output length should be > 512 bits, which ...
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1answer
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data migration: bcrypt to bcrypt different salts

I'm migrating passwords from one system (bcrypt) to another (also bcrypt) differing only in their salting. I noticed that encrypting the same plaintext password on one system generates a different ...
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2answers
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Storing email addresses in plain sight

What would be the best approach for storing a list of hardcoded email addresses in plain sight (in a public JS file or such)? The site is pretty low-key, for a small community of friends. Starting ...
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1answer
97 views

Is there a SHA-256 value which hashes to itself? [duplicate]

Getting curious about SHA-256 cycles (what happens if you hash a value repeatedly), I came across this question: Cycles in SHA256 The first answer suggests that using a 7-bit hash, it's possible to ...
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1answer
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Hashing using asymmetric cryptography

Every now and then, we read that some hashing function has been weakened or broken, but we almost never hear this for asymmetric cryptosystems like RSA or ECC. That's because while asymmetric ...
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Collision resistant hash functions with prime domain

In order to use RSA accumulator the elements must be primes. Is there examples of collision resistant hash functions with prime domain?
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1answer
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How to compute initial buffer of SHA-512?

I'm reading Cryptography And Network Security of William Stallings. In the SHA-512 section it is said that there is a 512-bit buffer is used to hold the intermediate and final result and every 64-bit ...
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1answer
93 views

“perfect” hash function [closed]

Does there exist any hashing function that has a different output for all of the messages? For example, let's say we have the function $H_{256}(x)$ Where $H$ is a 256 bit digest. Is it possible to ...
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Bad custom encryption

I hope you can help me understand the issue. I know creating my own encryption is not a thing which you should do, but I did this simple "encryption" a long time ago and discussed it with my teacher. ...
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1answer
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Security levels in NIST Post-quantum project: e.g. AES-128 vs SHA-256

In an article about NIST Post-quantum Standardization project I read about the security criteria of the proposed schemes and there was this table (Level I lowest security, level V highest): Level I: ...
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Solving encryption puzzle [closed]

I have this cryptography puzzle I'm stuck on, spoilers please with hints since I want to figure this out myself. I'm given that a code in the form of x:y:z is required to access a particular goal, ...
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1answer
38 views

Problem with Hash-DRBG's seedlen values (and others)

In NIST-SP-800-90Ar1, the Hash-DRBG is instantiated with hash functions using strange values for seed length (seedlen) such as 440, 888. How are these values derived? How to derive values for other ...
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2answers
106 views

Fiat-Shamir transform: reliance on hash input by interactive proof

Peggy would like to prove to Victor that she knows the discrete logarithm of $y$ based $g$; that is, she knows $x$ such that $y = g^x \bmod p$. One round of the interactive proof protocol consists of ...
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61 views

Split hash for 2 keys

These are the steps: Hash ECDH shared secret with SHA3-512 Concatenate odd bytes and rehash with SHA3-512 for AES-256 key Concatenate even bytes and rehash with SHA3-512 for KMAC key Is this key ...
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1answer
64 views

If multiple hashing algorithms are chained together, is the compound hash function more collision resistant? [duplicate]

The DASH cryptocurrency uses X11, which is a Proof of Work hashing algorithm composed of 11 separate hash functions which are run as a sequence. Example: $Digest = H_{11}...(H_3(H_2(H_1(Input))))$ ...
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1answer
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What if the hash code of the genesis block (first block in the block chain) is changed?

If so, what would happen? And if not, what are some limitations to it? The reason I am asking is because I just started getting into the cryptocurrency and am very interested in the cybersecurity ...
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1answer
58 views

Swapping a single bit inside a 40 bytes inputs fed to keccak256. Is it safe to assume no change in the first 20 bytes can result in the same hash?

I have the following data (represented as hex from binary below) where the lower bytes is controlled by attacker in the second case : ...
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Colliding input to compression function

So I recently started to look into cryptography and found the following question to cryptography scheme using $T = E_{S}(S \oplus M)$ It is said that this is not secure because you can have a ...
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1answer
101 views

SHA-256 : Finding two strings that the first n bits of hash value are same [duplicate]

How can I find two strings that have the same hash value for first $n$ bits in SHA-256? I'm implementing it by Python and I have the following ideas and problems: Keep generating two random string ...
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1answer
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Group Signatures with VLR Revocation Check

I was reading the paper by Boneh et al. Link. The scheme describes what is called a Verifier Local Revocation Technique. The Scheme assumes that a Revocation List [RL] allows each verifier to check ...
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Is a number generator based on hashing an incremental string and a seed considered random? Part 2

Sorry I didn't put enough details on my last question, I didn't expect that there is really lots of factors, so most answers were left for speculations. In this question, I will give the scenario I am ...
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Is a number generator based on hashing an incremental string considered random?

Consider the following system 1 - fixed string as a seed, example "something" 2 - concat an increment number "something-1" 3 - hash it, assume it is "9f2054ea4d2c" 4 - take the first 3 digits to ...
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Is attack against secret prefix possible for messages of any size?

I am aware of message extension attack on MACs constructed with a hash function that uses Merkle-Damgård scheme. $$MAC=h(k,x)$$ I am interested if this attack only works if $0 ≡ x$ mod (hash input ...
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Secret key suffix vs HMAC [duplicate]

What is the benefit of using HMAC over hash with key suffix? I realize that using key prefix is a bad idea because it allows message extension attacks. When adding key as a suffix such attack ...
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1answer
66 views

What are the random variables in Universal Hash Function?

Universal hash function is defined as follow: $f_{(k_0,k_1)}(x) = (k_0\cdot x + k_1) \mod p$, where $p$ is prime In Wikipedia, it is mentioned that the above function is pairwise independent. ...
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How to show that a result of hash function and a random is computationally indistinguishable?

I want to ask: How to show that a result of hash function and a random is computationally indistinguishable If we denote $H(): \mathcal{X} \rightarrow \mathcal{Y}$ is a secure hash function, $m$ is a ...
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1answer
53 views

Password to password mapping

DISCLAIMER: I understand the question might be a bit amateurish due to my limited knowledge of cryptography but, please, bear with me for a minute. QUESTION: Suppose a user Alice generates a pass ...
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Hash function over numbers that preserve addition and multiplication

I wonder if there is a known hash function that for any $x$, $y$ which are numbers in a certain range with certain accuracy (I guess one can think of them as integers?), you can define two functions ...
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Difference between strongly universal and $\delta$ univeral hash functions

Define a family of strongly universal hash functions as: $$\forall x_1, x_2 \in \{0,1\}^n, \forall y_1, y_2 \in \{0,1\}^m, ~ x_1\ne x_2: ~~ \Pr_{h\in H} [h(x_1) = y_1 ~\text{and}~ h(x_2) = y_2] \le \...
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Can hash functions be used for asymmetric encryption? [duplicate]

Snuffle uses hash functions but it is symmetric key encryption. Can a hash function be used to let a client encrypt without knowing the private key, and the server decrypt using a private key? https:/...
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Is there a name for encryption which relies on repetitive calculation (=time) instead of a key-value? (e.g. block chain, hash value, block cipher)

Many encryption problems are fast to solve if a key, factor, exponent or something similar is known. Other encryption methods don't have such keys. E.g. a hash value of another value. It's used ...
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1answer
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Add a pepper to a hash: as a string or a buffer, and should I calculate a hash of a peppered plain text?

I'm using a bcryptjs to generate a computationally slow hash function for storing passwords: ...