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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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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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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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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Why does LastPass use exactly 100100 PBKDF2 rounds

LastPass encryption scheme is recently changed to use more PBKDF2 rounds, specifically 100100. This seems like a really weird number choose. From what I understand brute force time scales linearly ...
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KCV scheme that encrypts a hash over key and IV

Is there anything wrong with this key-check value scheme? This question is a follow-up to an earlier question of mine. In summary, I want to devise a key-check value scheme that will enable my ...
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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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Hashing high entropy key into AES format

If I have a high entropy key (ECDHE shared secret), what type of hash should I use to format this into an AES-256 key? Is Sha256 or Sha3_256 sufficient to maintain entropy or do I need to use a KDF (...
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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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How were the arbitrary values used inside SHA-256 algorithm determined?

I am studying the SHA-256 algorithm, and I am wondering something about it. How were the values used inside of the algorithm determined? Take a look for example at how the 16-64th Words are generated....
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CRC32 catches errors, but then what's the point of SHA?

If crc or CRC32 is specially designed to catch errors, then what's the point of SHA or md4-5 or any other hashing function? What I did was, I had a 190 mb png file (rendered in 16k resolution with ...
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Rationale of the SHA-256 sigma function definitions

When the sigma functions are defined in equations (4.4) and (4.5) in FIPS PUB 180-4, the defined functions show the traditional sigma summation symbol, with limits 0 to {256} and 1 to {256}. The ...
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Would SHA-256(SHA-256(x)) produce collisions?

Was reviewing some Bitcoin public-key hash literature and the use of RIPEMD-160 and the SHA-256 as below: RIPEMD160(SHA256(ECDSA_publicKey)) The Proof-of-work ...
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Is SHA256 resistant to second preimage attack?

I am looking into building a merkle tree algorithm and I need to know if SHA256 is resistant to second preimage attack.
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Has SHA256 been broken by Treadwell Stanton DuPont?

In a recent press release issued by Treadwell Stanton DuPont, the claim is made that their research laboratories have successfully broken all 64 rounds of the SHA256 hashing algorithm. They further ...
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Is the AES-GCM encryption using the SHA256 hash of the plaintext as IV secure?

I want to encrypt a list of unique values and I want the property of when I encrypt the same value I get the same ciphertext (determinism). The adversary only observes the ciphertexts of a unique set ...
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Hash key expansion

A hash H is given by H = SHA256(K + N), where K is an unknown 64 character hex key and N is a known nonce. The nonce N is then mapped to a final result R between 1 ...
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Using an AES-256-GCM key as a salt to SHA-256

Assume 256 bit keys are randomly generated and data is encrypted using AES-GCM-256 prior to being sent to a server. The goal is to enable the server to determine uniqueness of data it receives ...
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Statistical Analysis of Cryptographic Hashing Algorithms

I was wondering how can I use NIST Statistical Test Suite to check for the randomness of output generated by a cryptographic hashing algorithm, let say SHA-256? To be specific, how will I generate ...
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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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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 ...
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Is it possible to truncate AES output and keep uniqueness (no decryption needed)? [duplicate]

I would like to hash numbers less than 1000000000, so generally they could be stored on 30 bits. The aim is to obtain numbers that are not reversible, so my initial plan was to use SHA256 (with some ...
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Does every language's SHA256 implementation provide different result for the same value [duplicate]

Probably this is very naive question, based on lack of understanding but I was watching a video from Andreas M. Antonopoulos about blockchain, bitcoin and consensus algorithms and he asked for the SHA-...
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Bitcoin mining nonce and birthday attack

Having read the basics of mining and this about SHA256 (probabilistic?) partial preimage possible? and SAT solving - An alternative to brute force bitcoin mining, I have the following question: ...
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SHA256 creates a unique hash for two *.wim that have identical content - are there better methods for verifying *.wim contents? [closed]

I'm trying to verify that the contents of a Windows Image are identical for two WIM files; however, I think the timestamps for the file modifications are affecting the final checksums--even though the ...
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Collision resistance of partial SHA-256 hashes XOR'ed

My hashing algorithm computes the SHA-256 for each of 12 input strings and XORs them to get the final hash. Is there a risk of an attacker being able to forge 2 sets of inputs that yield the same ...
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Do I still need SHA256 if I already had a AES 256 key that is 44 characters long?

Several months ago, I was required to research on AES and SHA-256 to make a secured license system for my app. However, I was dumb enough that couldn't distinguish between the 256 bits from AES and ...
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SHA-256: One input, two different outputs?

I am new to SHA-256. I have discovered that the same input could produce different SHA-256 hash ouputs depending on the (online) device I chose for generating the hash. Is this normal, or is there a ...
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How does sha-2 with fewer rounds work?

The wikipedia page about sha-2 states: Currently, the best public attacks break preimage resistance for 52 out of 64 rounds of SHA-256 or 57 out of 80 rounds of SHA-512 How exactly is the sha-256 ...
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Hashing a hash for authentication

I currently use Argon2 to derive a key (I will use a salt which I will save in a file as plaintext for when I later need to derive a key again) from a given password which I will use to encrypt a file ...
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Suitable 16-bit checksum?

I am writing a toy1 transport protocol and I am trying to implement a feature whereby: A 16-bit checksum is included in every packet. This checksum can be extended to be 48-bit if the data is large, ...
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Is it possible for a hash in SHA-256 to have more than 8 digits? [closed]

Is it ever possible for a hash to have more than 8 digits in SHA-256?
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Why initialize values and array SHA256 with specific buffer?

Why initialize values and array SHA256 with specific buffer? ...
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How is the hash for a file calculated?

Is the file just read bit by bit to calculate the hash with those values or is there more to it? Are there any resources to read a bit more about file hashing?
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SHA256 message schedule examples

I need some example values for the message schedule stage of SHA256 to test this part of my implementation. If possible in binary, for the string 'abc'.
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For the hash computation of SHA-256, is it computed in parallel or series?

I'm trying to write my own SHA-256 implementation in VHDL, which runs in parallel execution style I have been using this as a reference to the SHA-256 algorithm: https://www.researchgate.net/file....
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ECDSA signature of a random 32 byte number vs. the hash of the number

I'm working on an application that involves signing a 32 byte random number generated by the OS. Assuming the RNG works as intended, is it safe to sign the random number itself rather than a hash of ...
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Bitcoin mining: how is a block header of 80 bytes processed in SHA-256? Isn't it too big?

The whole process of bitcoin mining was making sense to me until a moment of madness an hour ago, if there are 80 bytes of data to be processed in SHA-256, that's 640 bits of data to be processed in ...
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Use a hash-function twice

I'm creating a small messenger and I wanted to know if it makes sense to store user passwords double-hashed in our backend-database. I wanted the user the register in an app, which should save a hash ...
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Is there any Corelation between the SHA256 and SHA512 hash of the same data?

Is there any Corelation between the SHA256 and SHA512 hash of the same data ?
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What is the difference between SHA-3 and SHA-256?

I am new about cryptography, I learned that SHA-3 (Secure Hash Algorithm 3) is the latest member of the Secure Hash Algorithm family of standards, released by NIST....
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Is it possible to unhash sha256 if you are given the sha256 and unhash of a variable? [closed]

Lets say that $a, b, c$ are variables and you know that $$\operatorname{sha256}(a) = b \\ \operatorname{decrypt}(b) = a \\ \operatorname{sha256}(b) = c \\ \operatorname{decrypt}(c) = b$$ Is it ...
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What does the symbol $W_t$ mean in the SHA-256 specification?

I'm really confused about the computation about SHA 256. $$W_t = \begin{cases} M_t^{(i)} & 0 \leq t \leq 15 \\ &\\ \sigma_1^{256}(W_{t-2}) + W_{t-7} + \sigma_0^{256}(W_{t-15}) + W_{t-16} &...
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How to prove that finding a cycle in a cryptographic hash function is hard?

I want to show that finding cycles in a cryptographic hash function is hard. My thought: assume there a black box, that given a cryptographic hash function $h$, finds some $x$ and $r$ in polynomial ...
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Can i generate a SHA512 hash if i know the SHA256 hash of some unknown data?

if the SHA256 Hash of some unknown data is known ! Can i find the SHA512 of that unknown data ?
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Is SHA-256 OK to use for key derivation for a key that is never persisted?

The scenario: On the one side a user enters a pass phrase to encrypt a stream of data (AES-GCM) and a symmetric encryption key is derived from the pass phrase using plain SHA-256 (so not a slow ...
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Is reverse engineering SHA256-HMAC function possible? [duplicate]

Assume HMAC function is used to generate a 6-digt integers time-based onetime password. As follows: $$K_h =\operatorname{HMAC}(k,t) = H((k\oplus\text{opad})\mathbin\| H((k\oplus\text{ipad})\mathbin\|...
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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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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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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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