# 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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### Is the security of output of Skein when using arbitrary output size similar to that of SHAKE?

Let's suppose I have a 1MB high-resolution photo and I want to hash and create a 1536-bits key. I know that I could just use SHAKE-256 as its a pre-enginered way for doing that. There is also Skein ...
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### What would be the expected performance of hashing a seed with counters and using its keystream compared to SHAKE-256?

Hashing a seed with SHAKE-256 and setting the output size to 1GiB it takes 6.5 seconds on my system: ...
644 views

### How can a preimage attack on SHA-256 always succeed within 2^256 evaluations when done though brute force?

I was reading the Wikipedia page for SHA-256 (SHA-2) and came across the following statement: For a hash function for which $L$ is the number of bits in the message digest, finding a message that ...
143 views

### Is SHAKE hash function seekable when using it as a stream cipher?

I searched a lot for this information in search engines as well as taking a look in the SHAKE reference implementation. If I decide to use SHAKE as a stream cipher, can I access a specific part of the ...
421 views

### Is the sum of hashes a suitable hash for sets?

Let $H: X \rightarrow \{0, 1\}^b$ denote a cryptographically secure, $b$-bits hash function on a set $X$. Let $H^*: \mathbb{P}(X) \rightarrow \{0, 1\}^b$ be a function on the power set of $X$ defined ...
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### How to prove that a line belongs to a final hash without knowing/re-hashing all other lines?

Let's suppose : I have a record/database (D) of 754 lines and each line correspond to a SHA256 hash.(Hn) I hash all this record to a final and unique SHA256 hash like this : ...
137 views

### How to prove that two hashes correspond to the same original message, without using the message to verify?

Let's suppose this: Message is "I love crypto.stackexchange.com" (M) Bob creates hash H1 with the message M and his private key (Priv) Alice receives a message X, and hash H2 with message X ...
1 vote
59 views

### Hashing a seed together with a block counter and using as a encipherment scheme: What scheme is more secure in practice?

This question is related to this (but it is not the same). Let's suppose I have a seed with an entropy of 1024-bits and hash it with a counter using a hash function with one-quarter of the seed size ...
202 views

### Conditions on a cryptographic hash function for Randomness Extraction

Assume we want to transform semi-random $n$-bit inputs into shorter $k$-bit outputs computationally indistinguishable from uniformly random bit strings, and there is (in some sense, to be specified) ...
1 vote
212 views

### Can I use a cryptographic hash function such as sha256 for Randomness Extraction [duplicate]

I want to transform a semi random input to a shorter, uniformly random bit string. Assuming there is enough entropy in the semi random input, can I use a collision resistant hash function to extract ...
1 vote
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### Hash function collision resistance

I have a course work for university, and am not sure on my answer so if anyone could please take the time out to read the question and my answer to let me know if I'm going in the right direction that ...
1 vote
104 views

### Mod operation while verifying an ECDSA signature with SECT233R1

I'm trying to perform ECDSA verification in hardware. I'm using the SECT233R1 curve (NIST B-233). I have a question about the hash function used while doing so. I want to use the SHA256 hash function ...
1 vote
159 views

### AES-CBC collision resistance of hash function [closed]

I'm very new to cryptography and am having some issues with the following question ...
131 views

### Using TEA to build a hash function

Background: TEA uses a 128 bit master key $K_{0\ldots3}$. All odd rounds use $K_0$, $K_1$ as the round subkey, and all even rounds use $K_2$, $K_3$. One cycle of TEA applied to the block $A_i$,$B_i$ ...
134 views

### Is WPA2 collision-proof?

I was experimenting with hashcat and aircrack to test WiFi security. The WiFi AP is a WPA2 encrypted network. The tool I used to ...
222 views

### Generic attack on Hmac sha256

Is there any generic attack on HMAC SHA 256 ? I am currently reading up on attacks on Hmac sha-256. However most of the papers I've found are about side channel attacks such as Differential power ...
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### Password hashing and salting with SHA-256 on $2^{64}$ password space

If a password is randomly chosen from a space of $2^{64}$ passwords and is stored as an SHA-256-bit hash and a 128-bit salt, how many hashes does an attacker need to perform to recover the password in ...
1 vote
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### How many hashes to recover a salted password? [closed]

If a password p is selected from a space of 2^64 passwords, and the server stores this as a hash, h = SHA-256(p||s) where s is a random 128-bit salt. How many maximum hashes would an attacker need to ...
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I was reading this post https://senderek.com/SDLH/ about Shamir's hash function, which is defined as follows: Let $p,q$ be positive prime integers and let $n=p\times q$. Let $\ell = \mathrm{lcm}(p-1, ... 0 votes 1 answer 40 views ### Why would be the use of such hash function definition? What would be the input of these functions?$ G \space is \space an \space elliptic \space curve \space group \space G \space with \space order \space q\$ and three hash functions are defined as this: $$H_1: \{0,1\}^*\times G \rightarrow Z^*_q ... 2 votes 2 answers 232 views ### What drivers are causing an increase in authenticated encryption modes? So I'm currently working through this cryptography question and so far I have the answer of an increase of hackers due to increase in computational power. But apart from that I don't know what else. ... 2 votes 1 answer 276 views ### How do Pre-image, Second pre-image and collision resistance actually work? How does this affect data integrity? I'm working on this past exam paper and found this question about pre-image resistance and its relation to data integrity: Displaying the hash of a file on a website in order to provide data integrity ... 3 votes 1 answer 268 views ### Is SAT the mathematical problem behind SHA-2 and SHA-3? When I'm convincing non-believers that crypto is secure, I have a hard time with hash functions and the associated block ciphers. It is easy to show why RSA is hard to crack: I multiply two small ... 2 votes 1 answer 126 views ### How does the SWIFFT algorithm relate finding hash collisions to a lattice problem? I've been messing around with lattice based cryptography and came across the SWIFFT algorithm, a provably secure cryptographic hash function which has a security proof stating that finding collisions ... 0 votes 0 answers 389 views ### What hashing algorithm is fast and good enough for checking if source data is changed? Not sure if this falls into crypto from contextual point of view but it is about hashing algorithms. I have two directories -- assets/ and cache/. Anytime there is a file added, deleted, or changed in ... 0 votes 1 answer 69 views ### Modular hashing confusion I am trying to learn about basic hashing using the modulo operator and am a bit confused. In the text that I am reading, it says that the modulo operator can be used to accept an input of any length ... 1 vote 1 answer 836 views ### Why is \operatorname{Hash}(x \oplus y) not a secure proof-of-work algorithm? x is challenging string, y is proof string. \operatorname{H} is the proof-of-work (pow) function, to find a y such that H(x,y)<2^{256}/D x ,y = \{ 0, 1 \}^{512} \operatorname{H}(x,y) =... 1 vote 1 answer 361 views ### KEY using AES-128, If P is less than 128 bits, padded with 0 and create 128 bits, any problem if average pw length is 6 For communication between the client and the website, use password (P) as the key using AES-128. If P is less than 128 bits, it is padded with 0 to create a 128 bits key. is there any problem with ... 0 votes 2 answers 92 views ### Is there any way to claculate the hash of (a + b +c)) if you only know hash(a) and Hash(b) and Hash(c)? For example, if you have say, 3 distinct paragraphs of clear text a, b, c and you only know hash(a), hash(b) and hash(c), and then you have a clear text d, which claims to be the concatenation of a, b,... 3 votes 2 answers 407 views ### Is a simple KMAC-128 or KMAC-256 hash secure as a KDF? Context I am trying to build a simple protocol for key derivation. I want to use SHA-3 family hash functions, which (as far as I understand) should not be combined with HMAC because their security ... 2 votes 1 answer 488 views ### (How) can Argon2 be used to create both a hash for authentication and a secret key? The Argon2 specs claim that Argon2 can be used both for password hashing and key derivation. I want to generate from a single password both a hash for authentication and a secret key to use for ... 1 vote 1 answer 391 views ### Which hash functions provide 128 bit resistance? I was wondering out of the functions (MD5, SHA-1, SHA-256, and SHA-512), do all provide 128-bit pre-image resistance and 128-bit second-image resistance? Also, out of these hash functions, do only SHA-... 3 votes 1 answer 315 views ### Where is hash to curve used? I'm curious to hear of algorithms that use this new standard (there is a new IRTF CFRG Draft for it, for instance). It's useful for verifiably deterministic signatures on elliptic curves, but what ... 2 votes 1 answer 91 views ### Lattice-based Signatures and Hashes Although many different lattice-based signature schemes exist, Hash and Sign signatures schemes, like [GPV08], are prevalent. On the other hand, it is well known that collision-resistant hash ... 1 vote 1 answer 77 views ### Could I Use a Hash Function to Help Generate Cryptographic Key If I had a true random number generator that had a fault where 10-20% of the bits never change (these bits always produced the same value every time the TRNG was called), could I feed the result of ... 0 votes 1 answer 84 views ### Is it safe to initialize a random number generator with MD5 for pixel selection in image steganography? This question is related to "Is it safe to initialize a random number generator with MD5?". But in the context of steganography we don't know which pixels have been selected to hide ... 0 votes 1 answer 840 views ### Finding the private key with the transaction signature [duplicate] I have two ETH transactions (both belonging to the same address) that both have the same r value in the transaction signature, is it possible to extract the private key from it? Details of both ... 0 votes 1 answer 203 views ### How to prove that a hash function is collision resistant if it's equal to that of a collision resistant hash function? [closed] Given that H is a collision-resistant hash function from 2n-bit strings to n-bit strings. How do I prove that Hash is collision-resistant if:$$\text{Hash}(X_1∥X_2∥X_3) := \text{H}(X_1∥H(X_2∥X_3))$$ 0 votes 1 answer 84 views ### What is the difference between an ideal and a practical hash function? A user of this forum told about ideal and practical hash functions. What is the difference between them? Can someone provide examples of ideal and practical hash functions? 1 vote 1 answer 109 views ### Hashing a seed together with a block counter and using as a encipherment scheme: Will this have the same security in bits as the seed used? A user of this forum said that the whole entropy of a seed goes to the hashed result if using a counter and also that is suitable for key generation even if the internal state or digest size of the ... 0 votes 0 answers 32 views ### Proof of inclusion for odd-valued tree How would a proof of inclusion be done here as the number of nodes is odd and some hashes don't have a sibling hash? Normally you would send the sibling for each level to the client. Here there are ... 1 vote 2 answers 343 views ### Is it possible to generate a key from a hash function, being the key larger than the hash function digest output without spliting the seed? Let's suppose I have a 2MB photo and I want to generate a key from it, and the key should have 2048-bits of size. A hash function such as SHA3-512 would not deliver a key with with the desired ... 0 votes 1 answer 370 views ### Keccak Capacity bits Parameter I am learning Keccak Hash Algorithm and I am a little bit confused about the Capacity bits parameter. I am trying to understand how we can set the capacity parameters while implementing Keccak in ... 1 vote 1 answer 145 views ### What is the problem with having a hash to group function where you can find a discrete log relation between 2 different hashes? I was reading some notes on a naive hash to a group function. Consider a cryptographic Hash function$$H: \{0,1\}^{*}\to \{0,1\}^{k}$$Consider a Discrete Log Hard Group G with a generator g. We ... 1 vote 1 answer 120 views ### Are pedersen hashes of small inputs safe? I understand that the end result of a Pedersen Hash (like this one) is a point in an Elliptic Curve. In the example implementation mentioned above, the input M is split into chunks of 200 bits (the ... 2 votes 1 answer 93 views ### How to check whether function provides full diffusion or not? In "The Skein Hash Function Family" paper authors wrote: The MIX/permute structure has been designed to provide full diffusion in 9 rounds for Threefish-256, 10 rounds for Threefish-512, ... 1 vote 1 answer 600 views ### Is sha-256 better then sha-1 in aspects othen then the hash size? Assume I create a hash using SHA-256 and then take only the first 160 bits of the hash, as the result. is the result more cryptographically secured than SHA-1? Or are the two algorithms equally secure ... 4 votes 1 answer 190 views ### Alternatives of how the Fiat-Shamir transform random oracle is applied to a protocol The Fiat-Shamir transform typically works by substituting (public) coin tosses from the verifier by hashes of the prover's messages until this point, i.e.:$$H(x,\alpha_1) = \beta_1, \\ H(x,\alpha_1, \...
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Something like: $$h = Hash(\texttt{"Some String"} \mathbin\| h)$$