Questions tagged [sha-256]

SHA-256 is part of the SHA-2 family of hash functions with a 256-bit output and a 128-bit security level.

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Finding the IV values of SHA-256 given all message blocks

Given all message blocks $w[i],i \in 0:63$ and assume that $n<128$ (arbitrary) bits $x_1,x_2,...,x_n$ of the IV values are unknown (e.g., $h_7$ bits are unknown) while other IV values coincide with ...
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How is SHA almost Unique [duplicate]

I am trying to understand SHA in simple terms. For example let us assume there are only messages with maximum length of 4 bits (binery) in whole world. Number of possible messages with different ...
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1answer
88 views

Scrypt KDF cipher (scrypt CLI) - known vulnerabilities and cryptanalysis?

There is a scrypt cipher that is used for example by some cryptos like LItecoin for their mining algorithm. I never heard of scrypt. I know eg SHA-256 which is well analyzed and considered as secure ...
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5answers
388 views

Use a SHA256 as a key for AES256

Is it safe to use the SHA256 of a hard-to-bruteforce string as the key to encrypt data with AES256?
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1answer
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Does double hashing increase resistant against first preimage attacks?

Let's take Bitcoin as an example. Bitcoin uses SHA256, which can be vulnerable to collision and preimage attacks - although this is extremely unlikely to happen in the near-future. However, let's ...
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1answer
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“official” guidelines about the minimum length of a truncated hash

I am looking for some reference documentation suggesting a minimum reasonable length for a truncated hash (specifically, a truncated SHA-256 hash) to ensure preimage resistance. Obviously, truncating ...
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1answer
219 views

Hash function and Digital Encryption Algorithm

I am familiar with the fundamentals of cryptography as well as Digital Signatures. I understand how DSA like RSA works and the fundamentals of mathematics behind digital signing and verification. I ...
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3answers
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Does knowledge of SHA256(secret ∥ known constant) in addition to SHA256(secret) give any information about the secret?

Does knowledge of SHA256(secret) and SHA256(secret ∥ known constant) give any more information about the secret than just knowledge of SHA256(secret)?
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Chopping off SHA-256 entropy?

I have a NoSQL key-value database. I want to insert couple million of records to it. For the key generation, I'm, using a prefix (something like data-one-) and ...
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0answers
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SHA-256 digest space [duplicate]

SHA-256 is a well know hash function that creates digests of 256 bits. This means that the size of the digest space is 2^256 (or at least it should be), ie, the range of the digest space is: from <...
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1answer
518 views

SHA-256 Round Equivalence

I have calculated the average number of operations in 1 round of SHA-256 as follows: Additions: 9.25 Bitwise Rotations: 9 Bitwise Shifts: 1.5 Bitwise AND: 5 Bitwise XOR: 10 I have certain ...
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3answers
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Any weakness when performing SHA-256 repeatedly? [duplicate]

Is it significantly easier to reverse a SHA-256 hash if you know that the input was a 32 byte output of SHA-256? I assume for most outputs of SHA-256 there will be zero, one or two possible 32 byte ...
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1answer
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BigInteger imlementation requirement for SHA-256

Which BigInteger is needed for implementing SHA-256? SHA-256 has 64 hex symbols as output. I could use the data structure "string" to calculate the SHA-256 or a BigInteger. Do I need ...
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Minimizing exchanges for ZK proof of a message with given SHA-256

Consider the problem of proving knowledge of a message $m$ which has a certain public SHA-256 hash $h$, without disclosing $m$ or usable information about it, while minimizing the information exchange ...
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1answer
65 views

Does hashing a hash of a password over and over again increase its security?

I've heard of password cracking attacks using a list of commonly used passwords. Suppose in my situation, I can never be sure about the strength of the password, that a user inputs to my interface. So ...
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1answer
960 views

Base64 for a hash algorithm [closed]

It may be a silly question, but I am really curious. If a hash algorithm uses Base64 in the process of hashing a string, for example, it is still considered a hash algorithm, even though it uses an ...
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1answer
80 views

Partial key reveal for SHA-256 hash

Let's say I have a message 0123456789abcdefghijklmnopqrstuvwxyz which gives me the SHA-256 hash ...
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1answer
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What is the use of encoding a hash output?

In many applications, the MD5 algorithm is used which produces a 128-bit output which is represented as a sequence of 32 hexadecimal digits. This output is further encoded using a base62 or base64 ...
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1answer
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Does concatinating mutliple digests of hashes from CSRN result in a CSRN?

Kind of a noob question. Suppose; We generate 1,000 cryptographic-ally secure random numbers & store each of them in an array1. For each number in this array1, we take the hash sha256(CSRN) then ...
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2answers
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Single string producing two different hash results with SHA-256

Is it possible that a single string produces two different hash results after going through the same SHA-256 hash function? The code I'm working on right now is doing this, and I assumed this should ...
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1answer
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What are the consequences of removing a single byte from a sha256 hash?

I'm working on a system (Ethereum) where it is significantly cheaper to store 32 bytes than 33 bytes. I'd like to create a table where data is stored based on its hash. Sha256 would meet this ...
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2answers
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What makes SHA-256 secure?

For example, RSA relies on a mathematically hard problem, factoring, while ECDSA or similar rely on discrete logarithm problem. What makes SHA-256 and similar hash functions, of the same family, ...
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Idea behind internal SHA-2 functions

In the SHA-2 family, specifically SHA-256, there are functions called Sigma0 and Sigma1, which look like this: ...
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11answers
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How do hashes really ensure uniqueness?

This might seem an impractical and unnecessary conversation, but I feel it's something I need to clarify. Especially, as I just got my first developer job in a blockchain startup. So hashes are said ...
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2answers
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Read the result of the hash by SHA-256 as a number

I want to read the full output hash of SHA-256 as a number. How I can do it? Is it in the range of 0 to 2^256?
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1answer
64 views

Is iterative sha256 adequate for local password manager?

I'm fairly entry-level crypto; not a cryptographer by any stretch... I am at the level of ability to implement most of the traditional packages in python; the hashlib hashes and EAS, ECDSA ...
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4answers
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SHA512 faster than SHA256?

I'm getting this strange result that SHA512 is around 50% faster than SHA256. I'm using .net's SHA512Managed and SHA256Managed ...
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“One-Wayness” of SHA 1

I recently started learning about Hash Functions for my first time, and I've gone through and have tried to understand the SHA1 process. Brilliant does an excellent job of explaining it step by step. ...
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1answer
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Uniform distribution/randomness of characters in the SHA-256 hash?

I'm using the SHA-256 algorithm to generate a number in one of my programming projects. A SHA-256 hash is calculated from three strings: one the user can edit, one the user can view but not edit and ...
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1answer
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Do a 160-bit SHA-1 hash and a 160-bit slice of a SHA-256 hash have the same strength in terms of collision-free?

Take OpenPGP fingerprint for example. If the 40-digit hex standard remains unchanged, would it be helpful to upgrade SHA-1 to SHA-256 (but only taking the last 160 bits), in terms of reducing the risk ...
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1answer
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SHA256 output to 1-6 number range?

I want to calculate a random number (1 to 6) from the output of sha256. Can I assurance the probability of 6 abilities is the same?
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1answer
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Pre-Image Resistance of repeated, patterned SHA2-256 digests

Suppose $H = \operatorname{SHA2-256}$. Let $H_1 = H(\text{“Alpha1”})$. Let $H_2 = H(\text{“Alpha2”})$. … Let $H_N = H(\text{“AlphaN”})$. So all these digests are based off a common pre-image post-...
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The effect of truncated hash on entropy

Suppose I have a 128-bit random binary string (128 bits of entropy), then I hash it using SHA-256, then I take the first 128 bits of the output hash. Does the taken bit string still have (almost) 128 ...
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are there more efficient methods than HMAC to achieve convergent encryption?

I’m thinking about the convergent encryption system described in the top answer to this question. However, it seems like preferred modern HMAC algorithms like HMAC-SHA256 (as used in step 2 to create ...
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2answers
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If all encrypt algorithms in TLS1.3 ciphersuites are AEAD , why do they keep including a Hash algorithm?

In TLS1.3 all allowed algorithms included in cipher suites are AEAD, which means they don't just encrypt but they authenticate too (thus if I don't misunderstand, they give not only confidentiality ...
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1answer
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Are hash functions strong against quantum cryptanalysis and/or independent enough of mathematics?

I work on ethereum and other blockchain technologies. And seeing that quantum pc's are someday going to see the light I have some questions / doubts. I was wondering if hash functions are strong ...
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2answers
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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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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
899 views

Can someone give me an example of a Merkle–Damgård transformation?

I started reading "Bitcoin and Cryptocurrency Technologies - Princeton University" (coursera) and in the first chapter it talks about Merkle–Damgård transformations for SHA-256. I was trying to ...
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1answer
459 views

Is padding of the digest needed in SHA256 with RSA-2048 scheme?

For a signing scheme involving generating a $256$ bit digest using SHA256 followed by RSA with $2048$ bit modulus, the signature would always be 256 bit without padding even though signatures of up to ...
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1answer
254 views

Is it necessary to use single hash function for signature generation and HMAC?

I am trying to figure out if we need to use single hash function across all the places in a ssh session. i.e – signature generation/verification and HMAC calculation/validation. Is it possible to use ...
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2answers
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PGP digital signature vs SHA256 HMAC Comparison

First let me admit that I am not a mathematician or a cryptographer. I am responsible for assisting in making a recommendation on a project that is consolidating payment processes within a company's ...
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0answers
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Rotate values in predefined manner

I want to create a Server S1, that publish a different value every 10 minutes on the internet. The value looks something like f7826da6-4fa2-4e98-8024-bc5b71e0893e. ...
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1answer
304 views

Is it safe to hash a packet with a shared secret to prove authenticity?

I am developing an online game, where the server is written in Node.js and the client uses Godot. The issue is that Godot has no cryptographic functionalities (it can only encrypt and decrypt files, ...
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1answer
524 views

Use partial hash to verify entire hash

I've had an idea about storing parts of SHA256 hashes and I'd like to find out how secure it is, or how much less secure it is than storing the entire hash. For example, users can share this list of ...
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2answers
146 views

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
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Would a non-envelop, prefix only, SHA2 built MAC be susceptible to key recovery attacks?

When aiming to build a MAC, classic literature discusses the use of Envelopes or key "Sandwich" to build MACs. These were proved to be as secure as HMAC in “Sandwich” Is Indeed Secure: How to ...
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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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Cycles in SHA-256

Let's say I start with a particular 256 bit value. Call this $v$. I then hash that value, and get another 256 bit value. Call this $\text{SHA256}(v)$. I take this value and get another 256 bit value. ...
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1answer
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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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