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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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Steganography question about pixels [on hold]

You ae given the following phrase "Stop Now" and you have a 100x100 pixel image where each pixel is represented as an 8 bit gray-scale quantity. With these pixels below, show as much as you can hide ...
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1answer
100 views

Is there any bias whatsoever in modern hash function outputs?

We know that the output bias of a randomness extractor is $ \epsilon = 2^{-(sn-k)/2} $ from What is the relationship between entropy conditioning and final output bias in a TRNG?. The following is a ...
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How to compute hash value on cipher text using hash function? [on hold]

Please kindly help me, I would like to compute hash value on cipher text.
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39 views

How to ensure integrity of encrypted data having hashes only?

Having: plaintext $P$ a hash function $H$, encryption $E$ with key $k$ $h_p = H(P)$ and $h_{E_P} = H(E_k(P))$ Is there an encryption scheme $E$ or hash algorithm $H$ that allows proving that $h_{...
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186 views

How difficult is it to guess a salt based on a hash and known plain text?

I have the following use case: Alice owns the domain alice.com and Bob owns bob.com. I want to users to create a hash for ...
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1answer
49 views

Encrypted Database

I'm trying to build a encrypted database where we cant trust on the database manager. And since encrypt data in a deterministic way is bad, attackers can recover information doing frequency attacks, I ...
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1answer
53 views

Partial Known Message Pre-Image Attack on SHA-1

If the last 448 bits of a sha1 block input are known (only the first 64 bits are unknown). Is it possible to do a preimage attack using SAT solvers or something else? Or do I have to brute force all $...
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Length extension attack for file download

I am trying to understand the length extension attack. I found this tutorial where the author performs length extension on a file download URL. Original URL: http://example.com/download?file=...
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How does Argon2id store salts in PHP? [migrated]

The PHP implementation of Argon2id generates a salt for the developer. How does the application keep track of this salt? As a developer, how do I account for backups and otherwise ensuring that I don'...
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1answer
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Is a hashing algorithm considered broken if a collision happens under $2^{n/2}$?

If for example we would find a hash collision for SHA256 with $h(x) = h(x')$ for $x \ne x'$ and $x, \space x' < 128$ bit (meaning both $x$ and $x'$ are smaller than 128 bit), would SHA256 be ...
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1answer
181 views

Can we estimate the loss of entropy when applying a N-bit hash function to and N-bit random input? [duplicate]

Someone pointed out recently to me that a cryptographic hash function " is not designed as a bijective mapping from N bit input to N bit output". So if I feed an N-bit cryptographic hash function ...
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2answers
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Integrity check of a binary firmware file with hash function

I need to provide a mechanism that it is possible to verify the integrity of a firmware image flashed on an embedded system. The procedure should be, that if someone has doubt on the firmware’s ...
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1answer
51 views

Is a hash more or just equally representative of the first [hashlength] bytes of the hashed one-time pad?

[Clarification edit further down.] To distinguish already existing one-time pad files by their content instead of just their name ... ... is hashing meaningful? Or would the first X bytes (Length ...
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1answer
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If I hash ABC123, where ABC123 appears five times inside the file, will each of the five instances of ABC123 appear as identical hash values? [closed]

If I hash the word SOUND, where the word SOUND appears five times inside the file, will each of the five instances of SOUND appear as identical hash values?
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Participant workflow in the Cryptography competitions [closed]

I learned about the NIST hash function competition which generated SHA3. It says it inspired a Password hashing competition too, which resulted in Argon2. What I'm wondering is what people generally ...
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Original papers for hashing functions

I would like to learn how hashing functions are discovered / created. In part of this process I think it would be helpful to see the original works or papers of any authors of cryptographic or non-...
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2answers
490 views

How can I hash an input into an arbitrary domain point?

I am trying to implement a signature scheme involving RSA signing of a message digest generated by SHA-$256$. I want to hash the input into an RSA domain point instead of the fixed $256$ bit digest ...
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1answer
472 views

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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1answer
100 views

How to change hash checksum of a text file without changing the contents in the file

I have created a text file called test.txt and the content of the file is Hello World I would like to change the SHA checksum hash without modifying the contents and filename. Is there any way to do ...
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2answers
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Using a hash function as a random number generator

Using MD5 or SHA1 for instance, and applying integers (as seed so to speak) to the hash function, in sequence, and only keeping, say, the first 64 bits of the resulting hash, do we always have a ...
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2answers
235 views

What do the security definitions of SHA-3 mean, quantitatively?

In the SHA-3 standard (page 31) the security of SHA-3 is defined quantitatively, for example, they are saying SHA3-256 provides 256 bits of preimage resistance. How is this number of bits to be ...
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1answer
113 views

How to safely derive a value from a secret?

I have a use case of symmetric encryption with a single-use random key K known only by the sender and the receiver: In my scheme, Bob is able to send beforehand a tiny amount of information to Alice. ...
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2answers
102 views

Why is this MAC flawed?

Consider a function to create a tamperproof cookie as follows: $$\text{cookie}(m, k) = m \| \text{hash}(m \oplus k)$$ where $m$ is a message provided by Alice, and k is a secret key known only to ...
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2answers
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Does the knowledge of SHA256(secret) and SHA256(secret + known constant) give any information about the secret just SHA256(secret)?

Does knowledge of SHA256(secret) and SHA256(secret + known constant) give any information about the secret than just SHA256(secret)?
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1answer
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Moni Noar One Way Function: What does input is partioned mean?

I am trying to understand An Implementation of Efficient Pseudo-Random Functions. There, the following hash function is defined: We define $\hat{h}=\hat{h}_{r}: {\{0,1\}}^* \rightarrow {\bf Z}_R$ ...
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1answer
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Difficulty of forging MACs based on linear functions over $GF\left(2^n\right)$

This is a homework question, therefore I'm not expecting full solutions, just general guidance. I want to build a one-time MAC using universal hashing. I defined my hash functions as: $h_{a,b}:\...
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1answer
57 views

Is it possible to guarantee a SHA-256 hash will begin with a certain 3 bytes?

I've found this online currency someone has built as a project and it's "miner" / Proof of Work algorithm is as follows: Generate 32 bytes of random data and hash it, store the original value and the ...
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39 views

Is text description of MD2 algorithm wrong?

I'm trying to implement MD2 from scratch of RFC 1319. It feels like there is a gap between steps 3.2 & 3.3. After step 2, the checksum C is appended to the message and never mentioned again. We ...
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How do chat applications encrypt group messages?

This question is about techniques and architecture. Apps as Telegram/WhatsApp offers encryption p2p on messages, but how does it work with groups? Example: One room(chat group) have n users(...
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2answers
100 views

SHA-1 collision for strings of two symbols

Is it possible to have strings of two (Unicode) symbols with equal SHA-1 hash? For example, smth like "ab", "ba".
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1answer
43 views

Is there an advantage to using a hash in combination with a key-derivation function?

Note: This question was originally asked at Information Security Stack Exchange, but was moved here due to a topic overlap. It is currently recommended by OWASP to use an adaptive key-derivation ...
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Which Auxiliary Hash Function to use for Pointcheval's mDP protocol

I study GKE+P group key agreement protocol presented on paper Flexible Group Key Exchange with On-Demand Computation of Subgroup Keys by Michel Abdalla, Céline Chevalier, Mark Manulis and David ...
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Prove I know a value v in a set s.t. K = H(v) [duplicate]

Is it possible to prove that I know a value v in a finite set, such that the hash of the value v is K. Where v is private and K is public
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1answer
63 views

What is the minimum message length to obtain the full potential of a hash?

Suppose I want to commit to a uniformly picked nonce of fixed length $n$ bits without revealing the nonce, so I use a secure hash function $H$ mapping messages to digests of length $d$ bits. Suppose $...
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2answers
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What makes SHA256 secure?

For example, RSA relies on a mathematically hard problem, factoring, while ECDSA or similar rely on discrete logarithm problem. What makes SHA256 and similar hash functions, of the same family, ...
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102 views

Is there any hash function that relies on integer exponentiation instead of XOR?

I'm trying to implement a hash function in an esoteric language that has no 32-bit or 64-bit operations. Keccak, for example, is too slow in that language. I'd need a design that minimizes the number ...
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1answer
51 views

Given a SHA-256 message block, is it possible to undo the transformation of the internal state?

Consider the transformation described in section 6.2 of RFC4634 ("US Secure Hash Algorithms (SHA and HMAC-SHA)"). Given the message block M(i), and hence the ...
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1answer
65 views

Message authentication vs entity authentication

Does message authentication authenticate the entity? If the answer is "No", because message authentications like MAC work with the shared symmetric key, then my second question is: Does a message ...
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1answer
151 views

What is the use of SCRAM-SHA-256 (over SCRAM-SHA-1)?

The Salted Challenge Response Authentication Mechanism (SCRAM) specified in RFC 5802 can use arbitrary hash functions to operate. The base version from RFC 5802 uses SHA-1. From my understanding, ...
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49 views

How to make my hash more robust to the brute force?

I'm using PBKDF2 SHA 256 with 100 000 iterations to generate a secret. I want to increase the cost of brute forcing the passphrase I use to generate the secret. I'm thinking of using scrypt after ...
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2answers
123 views

Early propagation of carries in the BLAKE hash function

The BLAKE paper uses round constants derived from $\pi$ to improve diffusion, even if the additions modulo $2^{32}$ are replaced with bitwise XOR when processing a null message and null initial state: ...
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1answer
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Number of preimages of hash function from bounded domain

Suppose we have an "ideal" cryptographic hash function $H: \{0,1\}^{n+k}\to \{0,1\}^{n}$ and a given bitstring $b\in \{0,1\}^{n}$, Can we estimate how many preimages $H^{-1}(b)$ there are? With ...
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107 views

SNARK-friendly one-way compression functions

I'm looking for a one-way compression function that is secure and efficient within a zk-SNARK circuit. The motivation behind this comes from these considerations: SHA256-compression is highly ...
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1answer
55 views

Are there any known security issues when doing the following chaining of BCrypt Hashes: 'bcryt(bcrypt(user-pw, work-factor1), work-factor2)'

I am currently developing a protocol which would be able to "upgrade" the strength of a bcrypt password hashes without the knowledge of the user-password so a system may upgrade it without user ...
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1answer
102 views

Partial collisions of hashes, why is this important?

There's a lot of work finding "partial collisions" in hashes, and "Parallel Collision Search with Cryptanalytic Applications" seems to be the go-to paper for this work. I'm trying to understand why ...
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1answer
95 views

GMAC vs HMAC in message forgery and bandwidth

Saarinen in his work GCM, GHASH and Weak Keys says that; The GHASH algorithm belongs to a widely studied class of Wegman-Carter polynomial universal hashes. The security bounds known (this and ...
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1answer
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What pieces of information do you need to unhash a key to find out the original message?

I am very new to the hashing world and despite hours of research (AKA Googling) I still don't understand this piece of information. What are the different pieces of information that are needed in ...
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1answer
103 views

Does Composition of compressing Collision Resistant Hash Functions $H^{*}=H_2(H_1(x))$ is Collision Resistant?

I'm trying to solve the following problem: Given two CRHF $H_1:2^{4n}\to2^{2n}$, $H_2:2^{2n}\to 2^n$, construct the following hash function $H^{*}=H_2(H_1(x))$ compressing from $2^{4n}\to 2^n$. We ...
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Difference between hash function

In some paper, the terms "cryptographic hash function" and "deterministic hash function" would appear? I'm wondering what's their difference, and are there some other types of hash functions? Like the ...
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1answer
94 views

Computational Complexity of SHA-3 (SHAKE128)

Please, I got the question "what is the computational complexity of SHA-3 (SHAKE128)"? What does that mean and how can I calculate that?? *I am using SHA-3 (SHAKE128) in my mechanism to hash fix ...