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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Is this simple Proof of Work algorithm based on SHA256 susceptible to length extension attack?
Each block's contents are hashed into 32 bytes using $\operatorname{SHA-256}$ (call this string $a$). In order for the block to be accepted, there must be a 256bit nonce (call this string $b$) ...
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SHA-256 Hash Crack
Suppose, If a SHA-2 hash does get broken completely with hardly any power, where would it get reported and is there currently a bounty on it?
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How to create recreatable hashes?
I recently stumbled upon a YouTube video explaining a casino game. In simple words, they randomly generate a multiplier for your initial investment. This multiplier is supposed to be backed by a hash ...
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70 views
Message Authentication Code (MAC) calculation using OpenSSL
I have (1) a cipher text (2) a key and (3) an IV. I need to find the authentication tag of the cipher text. It is known that the authentication tag is created with the HMAC-SHA256 message ...
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1answer
48 views
Concatenation in Merkle Trees
Consider a simple Merkle Tree with leaves alice +100 and bob +50. Using the SHA256 hash algorithm, the digest of the respective ...
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1answer
226 views
Risks of Using SHA1 Instead of SHA256 for RSA with OAEP Padding
I'm presently implementing a simple RSA-based encryption as follows in PHP (using openssl_public_encrypt):
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976 views
How insecure would a cipher based on iterative hashing be?
I was just wondering how the following construction could be insecure. I can tell that known-plain attacks are possible, but I'm not sure about anything else.
Let the user pick a password and hash it ...
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2answers
95 views
reversing hash function makes possibilities increase exponentially, yet there is a finite number of inputs. How?
When trying to reverse a hash function, there is loss, e.g.
a+b=c
given c=5, try to go back to a,b (previous step)
(a,b)=(5,0),(4,1),(3,2),(2,3),(1,4),(0,5)
but, ...
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63 views
Bug Bounty for a reversed Hash
this is just a general question, Is there is a bug bounty from the NSA or anyone else for reversing a SHA HASH, specifically SHA-256?
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1answer
60 views
Should I use HMAC to create a multiple part HASH token
I have a web API with a custom API authentication system that users each have a SecretKey and a public ApiKey. Using these two keys client(or user) can generate a token for the authentication on the ...
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2answers
70 views
Bringing a key to 256 bit by a hash algorithm
For example, if I use Rijndael for encryption, I have to specify a key of a certain length. For user convenience, I want the user to be able to use a key of any length. Then, to get the key to the ...
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1answer
67 views
Reverse SHA256 Hashed Value from Multiple Instances where Part of Hashed Value is known
I apologize in advance if this question has been answered already. However, I have not been able to find an existing answer - despite the case being pretty simple and common I imagine. Perhaps there ...
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150 views
SHA-256 doesn't follow a uniform distribution?
I have been playing with SHA-2-256 in Julia and I noticed that the hashes produced don't appear to follow a uniform distribution. My understanding of secure hashing algorithms is that they should ...
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1answer
105 views
How strong if I combine two hash functions, such as MD5(SHA256(input))?
If I try to do MD5(SHA256(input)), what is the strength of this so-called double hashing approach?
Is it as strong as SHA256, or as strong as MD5, or as strong as ...
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80 views
Can I use SHA256 from BIP39 passphrase for auth credentials?
I am working on an E2E encrypted app. I am using OpenPGP.js and storing public and private keys on the server. The private key is encrypted with a BIP39 passphrase which is stored in browser ...
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2answers
925 views
What is the difference between "Elliptic Curve Function" and "Hash Functions" like SHA256?
I am reading about bitcoin and I am a little confused about "elliptic curve function" and "SHA256".
Do they have the same properties? Can both be used to generate private and ...
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1answer
156 views
Does the signature length of RS256 depend on the size of the RSA key used for signing?
The following NodeJS code, when run (v16.8.0), logs 512 to stdout.
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3answers
160 views
$2^{64}$ versions of the same message
I am reading a textbook and in there they explain the property of hash functions. In particular, they give an example of how unlikely it would be to find a second input value that would match the hash ...
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2answers
100 views
Is it possible to get the SHA256 hash collision with partial known data
I have a text sentence that consists of 448 digits [0-9] [a-f] (in HEX format).
This text sentence is partially cut off, but I know the middle, and the beginning ...
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Protect PII in-transit via hash comparison
I'm being asked to provide a solution for my internal customer. All network communication is internal and no applications nor their servers are accessible via the internet.
REQUESTOR application will ...
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1answer
273 views
How to generate a circuit for SHA-256?
In "A Boolean Circuit for SHA-256" by Steven Goldfeder, the author gives a Boolean circuit for SHA-256. I find this method very complicated.
May I ask how to construct a Boolean circuit for ...
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2answers
65 views
When inputting a stream of raw binary values to a SHA256 hash and a value of 10000000 is encountered in the input stream, does the hash end?
I am acquiring binary data from a sensor and storing it in a file. As each byte of data is read from the sensor, it goes into a SHA256 hash. The length of the acquired data stream varies from one ...
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How to find the right data for generate a partial SHA-256
I have 12 bytes (5 fixed and 8 variable) of data that will be passed to SHA-256, at the end only the last 5 (most significant) bytes of the 20 generated are checked, is there a way to generate the 8 ...
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1answer
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API key generation technique
I am designing an web api which needs to grant access to various client apps via an api key sent as http header. I know, not really how it should be done but I have no control over this part.
My ...
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Uniqueness and Schnorr signatures
I am trying to analyse a "uniqueness" game around Schnorr signatures. The game is described in $\textbf{B.}$ and I try to provide in $\textbf{1.}$ and $\textbf{2.}$ some incomplete answers ...
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Generating certificate using ECDSA_P256 algorithm but with sha256RSA signature
If you have a look at a certificate encrypting google.com it advertises a 256-bit ECC key with ECDSA_P256 parameter. The signature algorithm is sha256RSA. I've been ...
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1answer
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Number of Legitimate Bitcoin Wallets from unsequenced set of 24 Words
If someone found a scrambled BIP-39 24 word sequence how hard would it be to determine the correct sequence that yields someone's wallet.
Are there multiple different unique sequences of the same 24 ...
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How does one construct a SNARK circuit for proving the knowledge of a SHA256 pre-image?
Usually one explains how the R1CS/QAPs and SNARKs work using examples of circuits with multiplication and addition nodes, and constructing polynomials from that is relatively straightforward. SHA-2 ...
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Matching accounts across multiple data leaks via their hashed passwords
I've heard about several instances where OSINT researchers were able to match user accounts from multiple data leaks purely based on their hashed passwords, assuming accounts had the same password on ...
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2answers
354 views
Doubt regarding converting hex to byte in SHA-256 input
Hash functions such as SHA-256 takes a binary string as input. Now given a hex string when we convert it to a normal text string the computed SHA-256 value would be the same. Herein lies my problem
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How to pad in the SHA256 Algorithm (an example using Bitcoin Header)?
For any bitcoin block we combine various Header fields to create a string which is an input to a 2 pass SHA algorithm. The resultant hash must match with the Hash in the Block header for the Block to ...
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1answer
68 views
A query regarding SHA256 Algorithm
I am trying to code SHA256 from scratch to understand its implementation based on the wiki pseudo code as its clear enough. But I am running into problems with the calculation of W[i] for the first ...
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33 views
If the source code of SHA256 hashing algorithm is available in public, why can't it be hacked? [duplicate]
If the SHA256 algorithm is public, why can't attackers use it to create more collisions rendering the algorithm useless?
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Does SHA-256 have (128-time + 128-space = 256-overall)-bit collision resistance?
First, we consider those hash functions that can actually provide 256-bit pre-image security, and not something like SHAKE128<l=256bits> where the sponge ...
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2answers
620 views
How to unhash sha256? Alternatives to brute force?
I know it's almost impossible to do, SHA256 is a one-way function that can't be easily reversed, just like there are operations that have no reverse, take:
$f(x) = x+5$ , it's easy to see that if you ...
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1answer
206 views
Does this paper find cryptographic weakness of SHA-256?
I found only the abstract and tables of this paper
https://dl.acm.org/doi/abs/10.1145/3409501.3409513
From the abstract
In this paper, the researchers proved that the modified SHA256 is viable to ...
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1answer
55 views
In sha256, is it possible to use less information than the full preimage to prove that the prefix of the preimage is a certain string
Alice split a long string P into two segments A and B. A is relatively short and B is long.
H = sha256(A + B)
Bob does not know P, but knows H.
Is it possible for ...
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1answer
58 views
Does my SHA-256 TableSalt algo give away the seed salt?
The Setup
I have a table of values for which I need to compute a salted hash for each table-cell value. Furthermore, I need the salt for each table cell to be unique and unpredictable. (I can explain ...
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2answers
70 views
is it safe to combine scrypt with other hash algorithms?
I'm currently writing a file encryption program, and I designed this scheme to derive a key from user input password:
...
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1answer
72 views
What is the role of SHA-1 on Diffie-Hellman-group1-SHA1?
I undersntand that in Diffie Hellman each party generates a public / private key pair and distributes the public key.
I know that a combined key is created with the sender private key, and the ...
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1answer
78 views
How do we know if someone has successfully discovered the steps of a hashing algorithm? [closed]
I was reading an article about how SHA-256 encrypts stuff (Here it is by the way) but how do we know the steps mentioned are true? I'm not a cryptography expert but I've tried making my own encryption ...
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1answer
141 views
Why are different private and public key generated in online brainwallets?
Why is that different wallet generating sites give different public and private keys when you enter the same passphrase even though they both use the same Algorithm (Sha 256)?
Thank you
P.S.
Ok...one ...
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1answer
154 views
sha256 - how many characters can we put in a message block?
since we can put 448 bit of the actual message in every block(56 characters), if I have a string of 56 charcters ...
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42 views
Is 64-bit SHA-256 IV-based MAC for fixed-length messages reasonably secure?
I want to use truncate8(SHA256-nopad(IV=secret, message)) as a 64-bit MAC, where message is guaranteed to be exactly one hash ...
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TLS1.3 transcript hash
From RFC8446:
For concreteness, the transcript hash is always taken from the
following sequence of handshake messages, starting at the first
ClientHello and including only those messages that were ...
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15 views
Can a hash function be cyclic? [duplicate]
Is it possible for a hash function, SHA256 for example, to be a cyclic hash function, where the hash of the hash returns the original value?
Example:
...
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AES CBC Encryption Key & Special ASCII characters [duplicate]
Can we add characters like α π Σ µ ...
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Is it possible that a SHA256 hash has the same hex character over and over again?
In theory, there are infinite inputs, that you can hash with SHA-256. So theoretically it would be possible that one hash string would read 0xaaaaaaaa...
But would ...
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How to generate different hash values for same files/messages?
I was generating HashValue for contents in the file. I want a different hash value every time I wanna generate even if the file is the same.
I am using SHA256. For the same files, the hash value I am ...
