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.

35 questions with no upvoted or accepted answers
Filter by
Sorted by
Tagged with
4
votes
0answers
68 views

Challenging $O(2^{n/2})$ for hash collisions using quantum computers

In "Finding Hash Collisions with Quantum Computers by Using Differential Trails with Smaller Probability than Birthday Bound" the authors Akinori Hosoyamada and Yu Sasaki state that it may ...
2
votes
0answers
59 views

Depth of $\operatorname{SHA-256}$ implementation by fan-in $2$ and fan-out $1$ Boolean circuits?

A fan-in $2$ and fan-out $1$ Boolean circuit is a circuit consisting of $\operatorname{AND}$, $\operatorname{OR}$ and $\operatorname{NOT}$ gates where number of inputs to $\operatorname{AND}$ and $\...
2
votes
0answers
21 views

How to find k-way second preimages

For example: Assuming someone has found a second preimage for SHA-256. In other words, for SHA256(M1)=H, someone has found M2 which SHA256(M2)=H Now, is it possible to generate k-way second ...
2
votes
0answers
71 views

Is there a reason behind the number of bit rotations used in SHA-256?

SHA-256 uses the following bitwise functions during the hash algorithm: $$\begin{align*} \Sigma_0^{\{256\}}(x)&=\operatorname{ROTR}^{ 2}(x)\oplus\operatorname{ROTR}^{13}(x)\oplus\operatorname{...
2
votes
0answers
579 views

Is this a secure (and correct) sign-then-encrypt technique for transferring messages?

After reading some information on the way iMessage works I have been working on writing some code to try my hand at securely transferring messages in a similar manner and I wanted to confirm that the ...
2
votes
1answer
910 views

Is it safer to use timestamp in REST authentication?

I am working on a personal project to build a REST authentication system which authenticate clients via three parameters: ...
1
vote
0answers
27 views

vec_sel in SHA-1

I can't find what is vec_sel() in this optimization from Wikipedia: Instead of the formulation from the original FIPS PUB 180-1 shown, the following equivalent ...
1
vote
0answers
141 views

How quickly can we compute SHA256?

Disclaimer. I have asked a similar question on Electronics StackExchange: they advised me to try here. The question I am in the process of developing a simple protocol whose security relies on the ...
1
vote
0answers
19 views

TLS 1.3 clarification needed on hello_hash and subsequent hashes

I am exploring TLS, mainly from the server side at the moment. I am creating a server that will authenticate a client using TLS 1.3 and eventually I will be creating a client authenticating to a ...
1
vote
0answers
77 views

Does fixing partial bits of a SHA256 hash increase the probability of finding a preimage using the meet-in-the-middle attack?

Let’s say I want to find a partial rather than full preimage using the meet-in-the-middle attack. For example, my goal is to find a preimage so that the first 76-bit output of the hash are all ...
1
vote
0answers
123 views

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: ...
1
vote
1answer
81 views

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-...
1
vote
0answers
81 views

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 ...
1
vote
0answers
92 views

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 ...
1
vote
0answers
336 views

Handling key invalidation

I'm writing an Android app which will need to store some data for the user as a byte array of unknown length. The data must be encrypted. I have gone down the path of the hardware-backed keystore and ...
1
vote
0answers
68 views

Hash function notations and their corresponding existing cryptographic hash algorithm

I am implementing Role-based access control by referencing the paper Enforcing Role-Based Access Control for Secure Data Storage in the Cloud. In page 6, they have mentioned to choose hash functions $...
1
vote
0answers
61 views

Keys and key-stretching when authenticating requests?

I'm making a REST application and still a bit confused about this issue. basically, to authenticate incoming requests, I give out userId, issued timestamp, expiry timestamp (normally 3 months after ...
1
vote
0answers
129 views

Designing an AES-based protocol for controlling and acessing ioT boards via RF

I'm designing an open ioT protocol to be used on ioT boards based on Texas Instruments RF-based MCUs. These MCUs have an AES module to easily encrypt and decrypt AES content, so that's why I choose a ...
0
votes
0answers
21 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 ...
0
votes
0answers
22 views

TLS 1.3 Finished message

I am looking to RFC8448 and at page 7 it says: ...
0
votes
0answers
23 views

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 ...
0
votes
0answers
16 views

Public Key Fingerprint: Preimage Resistance

In my system, “resources” are granted operational certificates signed by a particular CA. Each resource has a unique public/private key pair that it generates once. The operational cert granted by the ...
0
votes
0answers
45 views

SHA3_512 as dynamic SBOX generator

I'm creating a substitution-permutation cipher (for learning purposes only of course) and I'd like to implement dynamic SBOXs. The cipher will have a block size of 128, and 32 rounds. These SBOXs will ...
0
votes
0answers
47 views

Is this a good implementation of digital signature with timestamp?

Is this a good practice ?. How good or bad is this compared to appending a timestamp to the actual data and hashing it as represented below. ...
0
votes
2answers
70 views

Hash coordinates (back-end) without the client (front-end) knowing the coordinates, but to be able to guess them

So I have a set of coordinates and I will hash these with a random salt with SHA256. Coordinate range is 0,100. ...
0
votes
0answers
63 views

Can I and How Decrypt this Online

Although I had a security course in school a long time ago, I am effectively new to cryptography. I have an encrypted text, the encryption key of 44 characters, the encryption method, (Fernet, which ...
0
votes
1answer
76 views

Explaining the reason of radically more accuracy while using different set of hash functions instead of same set of hash functions on some operations

So I am looking for an explanation of an experiment. In this experiment, I took a set of k hash functions. Say the total number of data points I am working on is d. Call an algorithm A which used that ...
0
votes
0answers
125 views

Probability of collision when we use a particular part of sha 256 hashed value

So I was supposed to use hash some co-ordinates and I was supposed to use k 3-wise independent hash functions in order for the mathematical explanations behind that algorithm to be hold. But after ...
0
votes
0answers
48 views

Is Joux's multicollision attack applicable for truncated SHA256?

Joux presents an elegant way to generate k-way multi-collisions with about as much effort as generating a single collision: https://www.iacr.org/archive/crypto2004/31520306/multicollisions.pdf ...
0
votes
0answers
55 views

Should I update my fedora encrypted system?

I have installed my Fedora Workstation version 23 using native disk encryption. Since it, I am upgrading it using dnf system-upgrade plugin. Today, I have fedora 32. Some time ago, I’ve discovered ...
0
votes
0answers
130 views

Combining Hashes - NTLM and SHA

i have been recently learning about different types of hashing and the encryption/decryption methods of such hashes. Im currently trying to find the preimage of this hash i have been given as a ...
0
votes
0answers
219 views

Is it possible to reverse the final rounds of SHA-256

I've seen a lot of preimage and collision attacks on SHA-256 that target the first few rounds. So far, the best attacks break preimage resistance for the first 52 rounds out of 64 rounds. However, I'...
0
votes
0answers
483 views

How to bruteforce password from HMAC-SHA256 hash (if you have the key)?

Short of creating one's own script / program, is there an existing, readily available way of iterating through a list of potential passwords to find which one corresponds to a hash (HMAC-SHA256), ...
0
votes
0answers
359 views

Why initialize values and array SHA256 with specific buffer?

Why initialize values and array SHA256 with specific buffer? ...
0
votes
0answers
26 views

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. ...