# 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.

1,877 questions
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### DSA signature creation using hash oh the message

I am trying to understand how i can create DSA signature. the arithmetic uses H(M) and it is given a random nunber for the hashing result.( written- lets assume it is 121). Is the number really random ...
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### Do exist a one-way function that have 2 Condition?

Can anyone help me to prove this theorem that i can't prove it in a book that i bought it recently. If exist one-way function or OWF function: 1-exist a one way function ( withhas name $f$) such that ...
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### GMAC vs HMAC in message forgery and bandwidth

Saarinen in his work GCM, GHASH and Weak Keys says that; The GHASH algorithm belongs to a widely studied class of Wegman-Carter polynomial universal hashes. The security bounds known (this and ...
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### Difference between hash function

In some paper, the terms "cryptographic hash function" and "deterministic hash function" would appear? I'm wondering what's their difference, and are there some other types of hash functions? Like the ...
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### Why is $h(H, m) = E(m, H) \oplus m$ insecure?

I am taking a cryptography class on Coursera. I learned that the compression function $h(H, m) = E_m(H) \oplus m$ is insecure (even though other variants like Davies­-Meyer or Miyaguchi-Preneel are ...
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### Given a particular $1600$-bit output $Y$, is it feasible to find a $1600$-bit input $X$ such that $\text{Keccak-}f[1600](X) = Y$?

I have read this answer on Crypto.SE and I want to clarify a few details. Does this property of $\text{Keccak-}f[1600](x)$ imply that if we know a particular $1600$-bit output $Y$, it is feasible ...
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### 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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### Is there any way to check hash of homomorphic encrypted data?

I need some algorithm that satisfies: H - hash function Enc - encryption function (using public key) M - secret data $Enc(H(M)) = H(Enc(M))$ Let this system exist: the First person has a secret ...
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### Other than password hashes, are there other uses for non-reversible crypto

Hashing is useful for checking that an input matches expectations without giving away the stored expected version - so confirming passwords etc. But are there other use cases? In general, ...
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### What is a ratchet?

while reading Whatsapp's Security Whitepaper I found the term "ratchet". What does it mean in cryptography? The Message Key is derived from a sender’s Chain Key that “ratchets” forward with every ...
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### Are common cryptographic hashes bijective when hashing a single block of the same size as the output?

It's been said that CRC-64 is bijective for a 64-bit block. It the corresponding statement true for typical cryptographic hashes, like MD5, SHA-1, SHA-2 or SHA-3? For example, would SHA-512 be ...
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### Hash using AES and key 0

Consider the following hash function for a message x = x1||x2|| · · · ||xn: h(x) = Mn i=1 AES0(xi) = AES0(x1) ⊕ AES0(x2) ⊕ · · · ⊕ AES0(xn) where the key used in AES is k = 0. Can someone explain what ...
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### MD5 proving collision for the famous hexadecimal blocks

Below shows the hexadecimal pair which collides in MD5 (http://www.mscs.dal.ca/~selinger/md5collision/): d131dd02c5e6eec4693d9a0698aff95c 2fcab58712467eab4004583eb8fb7f89 ...
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### Blockchain cryptography

I'm a high school student doing a project about blockchain. I'm trying to figure out why hashing algorithms are crucial for the existence of blockchain and other types of cryptography wouldn't work. ...
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### Show that if a fixed key MAC is not collision resistant then the MAC function is not computation resistant for every key K

I'm really having some trouble with this one. Let $H$ be a MAC function. For every key $K$ we can create an unkeyed hash function (i.e.an MDC) by using $H$ to hash messages with the fixed key $K$. ...
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### How might one create a system of election by lot (sortition) that is both secure and verifiable?

I've been puzzling recently over sortition, a democratic method of selection for public office which I find very fascinating. Basically, instead of choosing candidates like Hillary Clinton or Donald ...
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### Proving/verifying keys for zero knowledge proof (zkSNARK) in a simple case (possession of a string whose hash is x)

I'm studying simple examples to understand how ZK-Snarks work. Following this great introduction, I'm trying to elaborate a generator function giving a prover and verifier keys: ...