# 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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### Hash multiset to point on elliptic curve where $A = 0$

I want to hash a multiset to a point on the elliptic curve $y^2 = x^3 + 3$ over a finite field of some 254-bit prime order, where $P = 3 \pmod 4$. Moreover, I want this hash to be incremental, in that ...
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### Second preimage attack complexity when the digest is malleable

An attacker has a hash $h$ and a message $m$. He wants to find $m^\prime$ with the same length as $m$ which hashes to $h^\prime$. However, $m^\prime$ can only differ from $m$ in the 1 bits (i.e. ...
1answer
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### Is it feasible to find n hashes that sum up to a given hash?

Consider two sets $A=\{a_1,a_2,\cdots,a_n\}, B=\{b_1,b_2,\cdots,b_m\}$; We can calculate the hash sum of those sets: $$HASHSUM(𝐴)=(ℎ𝑎𝑠ℎ(a_1)+ ℎ𝑎𝑠ℎ(𝑎_2)+\cdots +ℎ𝑎𝑠ℎ(𝑎_𝑛))$$ and HASHSUM(𝐵...
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### How many hash collision will exist where the digest is a pre-image?

This question follows on from the question Circular hash collision where digest is pre-image: Could hash(a) = b, hash(b)=c, then hash(c)=a? The question was answered but the issue of the number of ...
1answer
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### Circular hash collision where digest is pre-image: Could hash(a) = b, hash(b)=c, then hash(c)=a?

For any SHA-family of algorithms (including Keccak) except for SHA1, would it be theoretically possible for there to exist a pre-image a whose hash digest ...
0answers
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### What type of Encryption Is This? [closed]

I am currently working on a homework assignment. I am trying to find the password to the next level. I have it, but it is either encrypted, hashed, or scrambled. I do not know what type of decryption ...
1answer
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### When to use Argon2i vs Argon2d vs Argon2id?

I've read the manual, and multiple articles / StackExchange posts about this topic, but still can't decide which implementation of Argon2 is best for my use case. I want to securely encrypt passwords ...
1answer
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### How does concatenating diverse hash functions affect collision resistance?

Let's suppose I take 3 different types of hash functions and concatenate them for future safety so that: digest = Hash3( Hash2( Hash1( text ))) Does the birthday attack mean in this case that I must ...
1answer
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### Strongest collision resistance test?

An administrator is testing the collision resistance of different hashing algorithms. Which of the following is the strongest collision resistance test? A. Find two identical messages with different ...
1answer
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### Simple commitment scheme using secure hash function

Can I create a simple commitment scheme using a secure hash function? If so, is concatenation with a random secret enough to preserve hiding? (i.e. $C = H( random\_string || message)$) Thank you
1answer
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### Please explain me why we require $2^m$ & $2^{\frac{m}{2}}$ random messages

Assume that a one-way Hash function is secure and the best way to attack it is by using the brute force attack. It produces an $m$-bit output. Finding a message that hashes to a given hash value would ...
0answers
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### Recover secret SHA-1 constants given Oracle

There's a black box that's basically SHA-1, except that the constants (h0, h1,...,h4) are secret. We can pass it arbitrary inputs and get the corresponding outputs. Given this, is it possible to ...
1answer
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### Transfer and hide ciphertext with hash functions?

Can hash functions be used to transfer and hide ciphertext? This somewhat similar locked question, "If cryptographic hashes are completely unique, could they theoretically be used to transfer data?", ...
1answer
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### What is wrong with encryption-based / hash-based commitment schemes?

In the slides to my information security class it is stated without explanation that a encryption-based commitment scheme defined as follows is broken: Commit: P outputs c = Enck(m) Reveal: P sends k ...
1answer
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### Is the any QR code with built-in hash of the information?

For example, the text is something like "Hello world!" And after that text should be new line with hash (sha256): ...
1answer
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### would parallel crypto mining work

Hi everyone I was wondering would it be possible to mine a cryptocurrency like bitcoin in parallel. I have read a little about mining pools https://en.wikipedia.org/wiki/Mining_pool , But that's not ...
0answers
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### collision resistance of a composed hash function

Given a collision-resistant hash function $H(x)$, say SHA256, and I devise another hash function by $H'(x)=\sum^{m}_{1}H(x||i) \mod p$. The summation is defined on finite field of prime order $p$. ...
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### How does windows 10 v.1803 save the password in the SAM file? [migrated]

I'm doing a search on how windows 10 saves hashed passwords in the SAM file. From this article I suppose that Windows does this: If the password is 123456 and the user has RID 000003E9: CALCULATION ...
2answers
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### If hash functions append the length, why does length extension attack work? [duplicate]

I have understood that it's trivial to reconstruct the internal state of a hasher for many hash functions, if one only knows the output hash. Then, one can append data after the original data and ...
0answers
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### How is the PRIVATE KEY actually created in the first place? [migrated]

How is the "Private Key" created in the first place? I understand that once you have your wallet, you will also gain access to your public key and private key... But in order to have a wallet ...
2answers
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### Does a hash function have a Upper bound on input length?

I came across this Answer stating (just a line from the answer):- The input space is "infinite" and thus it has an infinite amount of values that will collide into a single hash And in the ...
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### Public Key VS Wallet Address - What is the difference? [migrated]

I am seeing a lot of contradictory information on why we now use Wallet Addresses rather than Public Keys. Some say that due to additional level of hashing (double hashing), Wallet addresses are ...
1answer
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### Difference between hash functions and algorithms?

Wikipedia lists "Hash function algorithms" within the "Hash function" page. I'm wondering what are the differences and if I can use the terms "hash(ing?) algorithm" and "hash function" interchangeably....
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### Security issues with computing parallel hashes?

One issue with most hash algorithms like SHA-256 is that it is inherently serial. You can't effectively use SIMD to parallelize a single SHA-256 calculation. However, you can calculate multiple SHA-...
3answers
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### How many bits in the resultant hash will change, if the x bits are changed in its the original input?

I came across a question stating: We have a message consisting of 10,000 characters. After computing its message digest using SHA-1, we decide to change the last 19 characters in the original ...
2answers
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### Cryptographic hash that supports efficient update after random-access plaintext modification

Is there a cryptographic hash algorithm that, given the hash of a plaintext, supports supports efficient recomputation of the hash after modifying a single byte of the plaintext? Specifically, is ...
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### hash tree merkle tree

If I have 32 blocks and I have a fault in two blocks, how many pieces should I touch to detect the error? I tried 20 blocks but this does not work? Anyone who knows what is the difference between ...
0answers
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### Zero knowledge proof - Hash [duplicate]

How can I prove that I know the input value of a given hash output without revealing the input? Say for example: sha256("abc123") = "6ca13d52ca70c883e0f0bb101e425a89e8624de51db2d2392593af6a84118090"....
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### Why there isn't a consistent key transform function of HMAC?

I am currently learning, the internal working of HMAC. There exists a key transformation process in the beginning, which works as follows:- Make the length of $K$ (Key) equal to $B$ (number of bits ...
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### A hash-based pseudorandom function

Let $H()$ be a cryptographic hash function. Question: Can we consider $c= H(r||i)$ as a pseudorandom value, where $i$ is a public value, $1\leq i\leq n$, and $r$ is a large uniformly random value/...
1answer
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### What is a good, easy-to-implement hash algorithm for avoiding hash collisions? [on hold]

I am working on a proxy dll for DirectX 9, and eventually DirectX 11, which dumps textures uploaded via the cpu to files on the disk. Crucial to some of the features I wish to implement is the ability ...
1answer
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### Toy one-way hash function for six digit number

I need to copy some data from a secure server to my laptop to work on it with a program (this description is very vague, I know). The data have six digit employee numbers and we are strictly ...
3answers
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### Are LRC (Longitudinal Redundancy Check) or CRC (Cyclic Redundancy Check) of any use in modern day computing?

I am currently learning about the history of Data integrity / Error detection. In the old days of tape drives, LRC was used for error detection. They were also used (at certain point in time) for ...
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### For a hashing function like MD5, how similar can two plaintext strings be and still generate the same hash?

When I say similar, I'm referring to the Hamming distance, the Levenshtein distance, or a similar string distance metric that measures how similar or dissimilar two strings are. For instance, are ...
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### “Work factor” and “iteration count” nomenclature in adaptive functions

In adaptive functions like PBKDF2 / bcrypt I often read people refer to "iteration count" and others refer to "work factor", and they seem to be used interchangeably (even though they're not - the ...
3answers
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### Can we assume that a hash function with high collision resistance also means a highly uniform distribution?

I want to use a hash function to generate a random sequence from number 0-n. And so I would like to find a good function that results in values that are seemingly random (does not need to be secure), ...
2answers
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### Does it make any difference when salting database passwords with Random vs SecureRandom?

I want to salt database passwords and then compute the hash but I wonder if I should use Random or SecureRandom? From an attacker perspective would it be easy to break if Random is used or ...
1answer
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### Hashing functions - How to define them?

Let $\mathcal{G}$ be a cyclic additive group for an elliptic curve $E\, / \ \,\mathbb{F}_p$, and let $p, n$ be two large prime numbers (e.g., we can consider $\texttt{secp160r1}$ with $p = 160$ bit ...
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### Cryptographic hash function based on logistic map?

Is there any secure cryptographic hash function based on the logistic map?