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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6
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3answers
472 views

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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2answers
431 views

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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1answer
481 views

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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0answers
256 views

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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2answers
548 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
1k 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 ...
2
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1answer
662 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 ...
2
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1answer
343 views

What should I use for consequent AES key derivation?

I am writing a small chat program to explore some methods and concepts in cryptography and currently I am using a shared AES key tunneled with RSA which upon further reading revealed many flaws both ...
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3answers
532 views

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)?
2
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1answer
389 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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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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1answer
2k 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, ...
2
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1answer
111 views

For two LUKS volumes made with the same password, can stealing the encryption key from one volume allow access to the other?

A running computer has two LUKS volumes that were made with the same password. One volume is open (key is in RAM), the other is closed. If the running computer is stolen, is the closed volume safe? ...
0
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1answer
224 views

How to name a signature algorithm that has no hashed component

I have an API-based service that digitally signs messages with RSA or ECDSA (system decides during runtime). The input is base64 encoded SHA-256 hash and the output is: signature of this hash ...
0
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1answer
160 views

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 ...
0
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1answer
678 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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1answer
4k views

Hash Collision Probabilities

Please give help! how can I calculate the probability of collision? I need a mathematical equation for my studying. Assume, I am using SHA256 to hash 100-bits. Thus: SHA256 {100} = 256-bits (hash ...
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1answer
4k views

Is it possible to convert the output of sha256 hash to binary or decimal value? [closed]

Can the output value of the sha256 hash function be converted to binary or decimal number? I know that the output is a set of 256bits. Is it possible to convert the output data to an unique ...
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2answers
604 views

If you wrote a reversible SHA-256 algorithm, how many “metadata” bits would be required for reversability?

I was reading about reversible computing while thinking about FPGA circuits. I realized that it would be possible to write a reversible SHA-256 algorithm if you stored some additional information as "...
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1answer
4k views

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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11answers
18k views

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 ...
5
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1answer
2k views

Is SHA-1 secure when used to implement a PRNG

I read SHA-1 is still a secured hashing function with no collision found as of now. However, it's just a matter of time for someone to come up with such a collision or attack. Therefore, in new ...
2
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1answer
472 views

Practical quantum attacks on SHA256 MAC and HMAC

Is SHA256 MAC (or HMAC) vulnerable to any quantum attacks? Game setup: The attacker's goal is to produce a valid MAC to be accepted by other devices in the ecosystem. The ecosystem consists of ...
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2answers
638 views

Can I find the IV of a single block of SHA256, given the plaintext and digest?

Each 512-bit block of SHA256 takes an initialization vector (IV) and message schedule and returns a digest. Knowing the message schedule and resulting digest, is it feasible to reverse the algorithm ...
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5answers
2k views

How many hex digits do I need to compare when manually checking hash functions?

I sometimes run sha256sum on large files after transferring them from one place to another, and will just skim the hash output to verify it's correct. But, I usually just look at the first/last 5 or 6 ...
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1answer
2k views

Signing with RSA-SHA256 algorithm using EC keys

Is it practical to sign a data using RSA-SHA256 algorithm with EC keys? I used a small NodeJS script and crypto module (uses openSSL internally) to test this and I could successfully sign the data and ...
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2answers
2k views

VeraCrypt a weak point [closed]

Biggest flaw in VeraCrypt(or other Encryption programs) is Hash Algorithm. VeraCrypt hashes (SHA,Whirlpool,Streebog) it is the only point where can break an encrypted disk. Because break algorithm (...
2
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1answer
126 views

Why is a 1 added after the message input and before adding padding zeros (if necessary) when using SHA256 or RIPEMD160? [duplicate]

In preparing an input for SHA256 or RIPEMD-160 a single bit (1) is appended to the message before adding any necessary zero padding and before adding the bitlength (64 bits) to form 1 or more 512 bit ...
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1answer
981 views

SHA's finite character set and collision

From what I've researched, SHA's hex encoded string contains the characters [a-fA-F0-9]. If we represent it in Base64, it can contain ...
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1answer
142 views

Does having an SHA256 hash compromise PBKDF2 secrecy?

If I have a password pwd, and I hash it with SHA256 and send it to a server for authentication (server will apply ...
9
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2answers
547 views

Which attacks are prevented by the different initial hash values for SHA-2 with truncated output?

NIST specified SHA-2 hash functions with truncated output. Those hashes use different initialization values than SHA-256 or SHA-512. SHA-224 is based on SHA-256. SHA-384, SHA-512/224 and SHA-512/256 ...
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2answers
165 views

Possible SHA-256 implementation weakness

I came across a SHA-256 implementation that seems not to conform to the standard and because I can't change the implementation I would like to know if it's safe for use or can be a potential weakness. ...
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2answers
1k views

Can I update sha-256 digest chunk-wise instead of the whole array at once?

I'm not sure whether this questions is about SHA-256 algorithm itself or the particular implementation I'm using. Usually, a hash algorithm implementation has functions, let us call them update and ...
0
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1answer
379 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, ...
2
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2answers
267 views

Does Diffie Hellman guarantee secrecy?

I am studying my Cryptology exam and one question I got stuck below; Recall the Diffie-Hellman key establishment protocol. Alice runs this protocol over the Internet to communicate with Bob. ...
2
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1answer
164 views

SHA-256 Hash identical on two similar but not exact items

There are two discs that we have that have all the same files. However, using a new method for burning the discs, the second disc had modified file dates of 5/30/2018 while the original disc has dates ...
2
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1answer
595 views

HMAC SHA256 for deriving session keys using random nonce

I need to derive session key in order to create an application layer secure channel between mobile app and a bluetooth device. My scheme is similar to this scheme that uses a HMAC and counter. ...
5
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1answer
664 views

Is it problematic to use PBKDF2-HMAC-SHA256 to derive a 512-bit XTS key?

PBKDF2 should only be used to generate a larger output than the hash function it uses if the output is used in such a way that it has a flat keyspace. As far as I am aware, XTS does not have a flat ...
11
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1answer
7k views

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 ...
3
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1answer
3k views

AES-CBC then SHA vs AES-GCM for encrypting and authenticating a web token

I am trying to have something like JWT but kinda ad hoc and encrypted. The token itself is simply a stringified JSON that contains the user ID and Unix timestamp. Now, I tried to use AES-128-GCM, ...
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1answer
96 views

How to reversely compute from hash [closed]

What are practical methodologies to derive the following ciphertext: 1bd0d370b262d748b21c40cc7e5746642b4c06079a224c65e443e429289753c2
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2answers
757 views

What would the implications be of a single randomly discovered SHA-256 collision? [closed]

Imagine if someone messing around with hashes accidentally came across two inputs to SHA-256 that produced the same output. Not a concerted effort, not Google/NSA or crypanalysis. No tin foil hats. ...
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1answer
459 views

How are multiple iterations of SHA-256 handled for longer inputs?

I wrote a python program to perform the SHA-256 function. It works just fine until I try to hash longer strings. If I hash (in HEX) ...
2
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1answer
389 views

Why is modulo being used for congruence in SHA-2 padding when the outcome is always the same?

I am reading up on SHA-2 algorithms and I came across this paper: https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf In section 5.2.1 it talks about the formula for padding a message. There ...
31
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4answers
31k views

How can hashes be unique if they are limited in number? [duplicate]

I'm curious, how can for example SHA-256 be unique if there are only a limited number of them?! For clarification: how many MD5 hashes are there? $16^{32}$ MD5 hashes can be produced. $16^{64}$ SHA-...
0
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1answer
3k views

Generating AES-256 Private Key from user string

So I wish to encrypt a string using AES-256 and want to provide the user to specify the password for unlocking the string. I plan to use sha-256 to hash to users entered password and use this as the ...
0
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2answers
681 views

In a very simplistic and step by step example, how do I get the 'w' values for SHA256?

I've been to https://docs.google.com/spreadsheets/d/1mOTrqckdetCoRxY5QkVcyQ7Z0gcYIH-Dc0tu7t9f7tw/edit#gid=1194752368, http://www.righto.com/2014/09/mining-bitcoin-with-pencil-and-paper.html, and https:...
0
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1answer
961 views

MAC size 128 bits or more?

Just a quick question: I've seen implemented BouncyCastle's class AeadParameters with MAC length of 128 bits, which was allegedly recommended. Though when I looked up HMac to implement my own MAC in ...
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2answers
2k views

Why SHA-256 (or any other) is too fast for passwords but “slow” for collisions to be found?

Normally, the standard answers of why passwords shouldn't be stored using a groups of hash algorithms, including SHA-256 or higher, even if salted, are "because they are 'fast' hashes", "the attacker ...

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