# 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.

1,944 questions
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### Capital passphrases with rainbow tables?

I'm currently trying to learn how rainbow tables work for a personal project of mine, but I am a little bit confused on how passphrases can be found. Here are the steps that seem do this, from the ...
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### 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?
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### Hashing based on the discrete logarithm problem

At a first look, one could use the elliptic curve discrete logarithm problem to grant for the onewayness of $H(x)=x*G$ (where $G$ is the generator point of the cyclic subgroup). Additionally, $H(x)$ ...
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### Concept of hashing a group of data and validating if a value exists within the group

When learning about cryptography and hashing, I remember seeing a concept where you could hash a number of values (ID's for example) and then validate against the hash, not storing the original IDs. ...
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### Backwards Length Extension Attack

Can SHA 256 be modified to make it vulnerable to length extension attack both by appending text to the front and adding text to the end?
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### rotation offsets for KECCAK-$f$[800]

So let's say you're trying to do SHA3-224. If you're on a 64-bit machine you'd presumably use KECCAK-$f$[1600]. In-so-far as I understand it'd have the following parameters: Rate: 448 (2*224) ...
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### Is it possible to prevent length extension attacks

Is it possible to prevent length extension attacks without using any other hash algorithm than SHA-1?
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### Cracking MD5, SHA1, SHA256 hashes [closed]

Hey guys i am trying to crack some hashes and it seems to be taking longer then expected (going on 7 days now). I am using John the ripper, I cant use hash cat due to pc limitations. I used online ...
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### Why is SHA2 used for file verification if it's susceptible to length extension attacks?

Am I misunderstanding length extension attacks, or is there some different reason, or is it really a bad idea to use SHA2 for file verification? If the answer is that it's really a bad idea, would ...
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### Security difference between $\mathrm{Keccak}(k\mathbin\|x)$ and $\mathrm{Keccak}(x\mathbin\|k)$

$\require{begingroup}\begingroup \DeclareMathOperator{\keccak}{\mathrm{Keccak}} \DeclareMathOperator{\concat}{\|}$According to Keccak's website, $\keccak(k \concat x)$ is safe: Unlike SHA-1 and ...