Podcast #128: We chat with Kent C Dodds about why he loves React and discuss what life was like in the dark days before Git. Listen now.

Questions tagged [hash]

A cryptographic hash algorithm is a function which takes a variable size input and produces a fixed size output. The algorithm makes it difficult to find two inputs with the same output or reconstruct the input from the output.

Filter by
Sorted by
Tagged with
1
vote
3answers
788 views

Which hash function is used for signatures ssh-rsa and ssh-dss?

I'm building a fuse client for ssh/sftp. I write the required ssh and sftp functions myself. Now I read in RFC4253 that before signing the data to sign is default hashed. In RFC4253 8. "Diffie-Hellman ...
1
vote
0answers
56 views

one hash for two (or more) different input values

(edit 21.11.2019): Verbosity of problem statement was to add context. I take the suggestion in comment and edit this question to have only mathematical problem. fgrieu succintly summarized the ...
1
vote
1answer
61 views

Supercomputer to crash hash

For NVIDIA TESLA V100 I know a hashcat performance for SHA1: it is about 17000 MH/s. Performance index for V100 is FP32 5120, FP64 2560. But what about supercomputers? For example Summit ...
0
votes
0answers
24 views

How to perform ByteSub transformation? [duplicate]

Can anybody please tell me how do we perform ByteSub transformation of AES to 01001001.
3
votes
1answer
242 views

Is length extension attack considered as collision?

I came across a few articles about length extension attacks on cryptographic hash functions. I was very surprised to read that SHA-256 and SHA-512 are prone to length extension attacks. This seems ...
1
vote
0answers
25 views

What does the server do on receipt of a one-time-password?

I'm trying to understand this question and I do not understand part of it. I have part of figured out, part of it not. Considering the hash function h(i) = (i + 5) mod 7, used in an implementation ...
10
votes
1answer
5k 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 ...
0
votes
0answers
20 views

AEGIS/MORUS as a general purpose hash function

Can AEGIS/MORUS, ignoring its output except the tag and with a fixed key and IV, be used as a general purpose cryptographic hash function?
-1
votes
0answers
27 views

Diffie-Hellman key exchange in four parties [on hold]

I understand the concept of 2 and 3 parties Here is the code of 3 parties ...
5
votes
2answers
160 views

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 "...
11
votes
3answers
1k views

Why is the core ChaCha primitive not good for use in a CRCF? Why create BLAKE?

Why is the core ChaCha primitive not good for use in a collision-resistant compression function (crypto hash)? Why go through the trouble to create BLAKE? What's wrong with using the core ChaCha ...
2
votes
2answers
151 views

Why not use chacha derivatives (BLAKE, rumba) to make an [H]MAC for use with chacha? Why use poly1305?

Why not use chacha derivatives (BLAKE, rumba) to make an [H]MAC for use with chacha? Why use poly1305? This question is especially interesting considering... "The security of Poly1305[...] is very ...
2
votes
2answers
55 views

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 ...
0
votes
0answers
13 views

Message Length Restriction in EIA3

EIA3 (EPS Integirty Algorithm) produces a 32 bit MAC value. The message length for this is restricted to 20000 bits. Quoting the document: The integrity algorithm (128-EIA3) computes a 32-bit ...
3
votes
1answer
136 views

Strength of key derived from a hash function considering the birthday attack

When a hash function is used to derive a key from a shared secret (either by simply hashing the shared secret or using a more robust construct like HKDF) what's the strength of the derived material? ...
2
votes
1answer
35 views

Merkle–Damgård transformation example

I m looking at this Example of Merkle–Damgård I have a similar question about this topic. I have hash function maps 256b blocks into 128b blocks, how many rounds are required for hashing a 140KB ...
0
votes
0answers
55 views

Encrypted vs unencrypted digital signatures [duplicate]

Is there a difference in terms of security between An encrypted stream of bits obtained by encrypting a plaintext concatenated with it's signature $ C = E_k(plaintext||\sigma)$ where $E$ is a ...
2
votes
1answer
3k views

Security of chameleon hash functions

With the knowledge of the trapdoor, we are able to compute the same digest for differents messages. I've read that given two messages $m$, $m'$ and two numbers $r$, $r'$ such that $Ch(m,r)=Ch(m',r')$...
-1
votes
2answers
306 views

Convert SpookyHash to semi-secure 192bit hash [closed]

What do you think of converting SpookyHash into semi-secure 192bit hash function by this way: increase security by using 8 * 8byte = 512bit blocks instead of 8 * 12byte blocks, but remaining 8 * ...
9
votes
2answers
12k views

Difference between salted hash and keyed hashing?

A cryptographic salt is additional input other than message itself for a hash function so that it prevents attacker from launching dictionary attacks . Usually the salt is stored along with the hash ...
2
votes
1answer
142 views

collision resistant summarizer for long hash values

how we can summarize SHA-256 into shorter values when we for example can't handle more than 128 bits on system? its better just use first 128bit and ignore the rest of bits or split full value and XOR ...
2
votes
1answer
216 views

Proof of shared secret through key derivation

Alice gives a random key $K$ (e.g. 32 bytes long) to Bob through a secure channel. Bob want to prove to Alice through an unsecured channel that he knows the key. Is it secure for Bob to send $s||KDF(...
3
votes
1answer
602 views

A fast non-cryptographic hash function that is “strong enough”?

I'm designing a simple one-time-password mechanism for authentication against a possibly-insecure server - i.e. I don't want to use symmetric shared secrets. The first idea that came into mind was ...
3
votes
1answer
3k views

Certificate signature with SHA-1 and RSA: where do 1888 bits come from?

Plenty of X.509 Certificates use "PKCS#1 SHA1 with RSA encryption" as the Certificate Signature Algorithm for generating a 2048-bit signature. The SHA-1 hash function generates a hash value of 160 ...
2
votes
1answer
253 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 ...
2
votes
2answers
3k views

Signing a document: which algorithm to use?

What I want to do is to digitally sign a document. I am new to cryptography and was wondering what issues to take into account. The only criteria is that a textual document signed should produce a ...
1
vote
5answers
931 views

Why do we need to compute message digest of a message first while signing it?

Why it is more efficient to compute a message digest of message and digitally sign it then, rather than sign the message directly?
1
vote
1answer
172 views

Hashing - Digital Signing and Trivial Stretching

Two very basic questions: 1. Digital Signing Why is it not possible to just simply replace the hash value from the request? Examples: ...
3
votes
3answers
1k views

Collision attacks on digital signatures

After reading this document about MD5 collision attacks, I still don't understand how collisions can make digital signatures insecure. In the paper, the researchers created two files with the same ...
2
votes
1answer
251 views

Generate hash value using public key along with message

I was trying to understand one way signature chaining on message by Saxena and Soh. As the message is passed from one user to other, every user can combine their signature to create one single ...
0
votes
1answer
700 views

1024 RSA Hash Signature attack. Forge a valid signature

I have an RSA signature of 1024 bit where i know the following: Public modulus N Public exponent (0x03) Cypher message Summary: An MD5 hash is calculated from a collection of byte and is used as ...
4
votes
3answers
1k views

Proof that a hash matches an encrypted file

Assume that Alice has a file $F$ which she is going to send, in encrypted form to Bob. Alice possesses $F$ and an encryption key $K$. She sends to Bob the encryption of $F$ using $K$, $E(F,K)$ as ...
2
votes
0answers
156 views

how to verify subset of hashes from hash list

I need to verify a couple hashed (SHA256) integers from a list of approximately 50 hashed integers in a message. The list can be divided into groups. The (plain) integer data is not in the message, ...
0
votes
0answers
25 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. ...
0
votes
1answer
568 views

What is the length of the SHA-1 message digest and how is RSASSA-PSS used for verification?

I am a newbie to cryptography and SHA-1. Currently I am configuring a SHA-1 hash function which takes default length as 128 bits. Is it okay to configure it this way, since I see in most cases SHA-1 ...
1
vote
0answers
59 views

Rotatable hash-based duplicate check

I want to check duplicates of secret information which is also already encrypted in our database(using ECC algorithm, one of the std curves). plaintexts can be phone numbers, zip codes, etc. Since it'...
0
votes
2answers
143 views

Reversability of Xor'd Values In Hash?

This may be a dumb question so please forgive me if so, but is a hash function considered one-way even if you have half of an xor'd value? For example say I have the values R and C, both are randomly ...
1
vote
1answer
57 views

Cryptographically secure hash function vulnerable to length extension attacks both to front and to back?

Is there any hash function where both $\text{hash}(m\|k)$ and $\text{hash}(k\|m)$ are vulnerable to length extension, but $\text{hash}(m)$ is itself secure?
-2
votes
2answers
267 views

How to determine if a Hash function is preimage resistant?

So I'm trying to solve this problem. There are of course more but I'm trying to figure out how would I even solve this first one in order to do the rest. Any hints or help in the steps would be ...
48
votes
11answers
16k 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 ...
0
votes
1answer
424 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 ...
1
vote
3answers
142 views

Digital Signature Algorithm for large files - bottle-necked by hash function?

I am new to studying digital signatures like ECDSA and EdDSA, and was curious about something. Lets say hypothetically I want to create a digital signatures of millions of files, with a total size of ...
2
votes
0answers
25 views

Strategies for fast integrity attestation over multi party computation for large messages

I am looking for ways to efficiently perform integrity attestation over large messages using multi party computation. While, hashing (SHA1, 256...) is one alternative but it's painfully slow and grows ...
0
votes
0answers
28 views

Security implications of an extra inner encrypt for a single block Matyas-Meyer-Oseas hash function

Was giving some thought to simple MMO constructions for fast single block hash functions for things like PQ crypto. There's Haraka, but that's not standard and readily available while simple AES is in ...
1
vote
1answer
35 views

Keyed Hashing and verification

Is there any standard algorithm where I can create a hash H(x,k) where x being the data and k being the private key. And verify on other end with H(x,l) where l being the public key? How it can be ...
0
votes
0answers
23 views

Designing a hash prediction model for a draw result, unmodifiable [duplicate]

I have to create a prediction model that forms a draw result of a prediction, essentially encoding the future draw result and the draw date. Then others will be able to check if the prediction is ...
0
votes
1answer
54 views

Password to password mapping

DISCLAIMER: I understand the question might be a bit amateurish due to my limited knowledge of cryptography but, please, bear with me for a minute. QUESTION: Suppose a user Alice generates a pass ...
4
votes
2answers
114 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 ...
1
vote
1answer
49 views

Zero Message Length HASH [duplicate]

What does it mean by a HASH of a message with zero length or rather why is it required? What could be a possible scenario where this is used? Also note that, for a given HASHing algorithm, the hash ...
0
votes
1answer
55 views

What's the proper way of fitting hash digest to encryption scheme?

I would like to know what is the proper way of fitting the hash digest to the prime in which the encryption scheme operates. regardless if the bits of the hash digest is larger or smaller than the ...