# 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.

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### What is the difference between an ideal and a practical hash function?

A user of this forum told about ideal and practical hash functions. What is the difference between them? Can someone provide examples of ideal and practical hash functions?
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### Hashing a seed together with a block counter and using as a encipherment scheme: Will this have the same security in bits as the seed used?

A user of this forum said that the whole entropy of a seed goes to the hashed result if using a counter and also that is suitable for key generation even if the internal state or digest size of the ...
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### Proof of inclusion for odd-valued tree

How would a proof of inclusion be done here as the number of nodes is odd and some hashes don't have a sibling hash? Normally you would send the sibling for each level to the client. Here there are ...
1 vote
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### Is it possible to generate a key from a hash function, being the key larger than the hash function digest output without spliting the seed?

Let's suppose I have a 2MB photo and I want to generate a key from it, and the key should have 2048-bits of size. A hash function such as SHA3-512 would not deliver a key with with the desired ...
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### Keccak Capacity bits Parameter

I am learning Keccak Hash Algorithm and I am a little bit confused about the Capacity bits parameter. I am trying to understand how we can set the capacity parameters while implementing Keccak in ...
1 vote
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### What is the problem with having a hash to group function where you can find a discrete log relation between 2 different hashes?

I was reading some notes on a naive hash to a group function. Consider a cryptographic Hash function $$H: \{0,1\}^{*}\to \{0,1\}^{k}$$ Consider a Discrete Log Hard Group $G$ with a generator $g$. We ...
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### Are pedersen hashes of small inputs safe?

I understand that the end result of a Pedersen Hash (like this one) is a point in an Elliptic Curve. In the example implementation mentioned above, the input $M$ is split into chunks of 200 bits (the ...
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### How to check whether function provides full diffusion or not?

In "The Skein Hash Function Family" paper authors wrote: The MIX/permute structure has been designed to provide full diffusion in 9 rounds for Threefish-256, 10 rounds for Threefish-512, ...
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### Is sha-256 better then sha-1 in aspects othen then the hash size?

Assume I create a hash using SHA-256 and then take only the first 160 bits of the hash, as the result. is the result more cryptographically secured than SHA-1? Or are the two algorithms equally secure ...
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### Create a control hash string from different sources, is there a difference, advantage or disadvantage in comparison when using this ways?

I wanna create from several inputs/sources should be formed into one hash value for controlling of different thinks later. Example: String + File String + String File + File String + File + String ...
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### How easy is it to identifiy the key when knowing a certain number of different AES-256/Fixed Nonce encrypted long-integers

Given some intervals of long integers (64 Bits). I need to generate alphanumeric strings which: should be used like passwords(known only by few individuals) must always be the same for the same ...
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### Avoid hash flooding without a secret key?

I'm currently building an implementation of the dynamo paper, yottastore. Imagine it as a huge, distributed, hash map. To find the node holding a key, I use rendezvous hashing (an improvement over ...
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### NIST example shows extra hexadecimal characters in Block Contents of SHA512-256

I was recently trying to gain a better understanding of the SHA-512/256 algorithm and on this NIST example they use the word "abc" as the input. In the Block Contents, it shows the expected ...
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### What is the minimum length of shortened HMAC to be considered safe?

Is it safe to truncate HMAC? What is the minimum length of a truncated HMAC so that HMAC is still considered to be safe to use? Are there any standards on when it comes to shortening HMAC? In my case, ...
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### Which of the following is a reason to publish files' hashes?

To valiate integrity or To verify if the software is digitally signed The question seems wrong to me. I do not see any reason to publish(make public) a hash. But it is in the material I am studying.
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### Hash tree that covers 16 data block

For a hash tree that covers 16 data blocks, how many hash checks do you need to perform to localize the error? Assume that error occurred on only one block.
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### Zk Proof to Prove that I know the secret x of y = HASH(x)

Lets say I know a secret value x. The hash of x, y = H(x) is public. Is there any zk way to ...
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### Should I use hash of passphrase as AES256 key

As title I have a password-like passphrase (8 chars at least) that is then hashed with argon2(with the salt is SHA256 of that passphrase). Then use it as AES256 key along with a random IV generated by ...
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1 vote
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### What should argon2id parameters be

I plan to use it locally on mobile devices. These seems to do not offer computational power as good as on a server. So what could be a secure argon2id parameters that run around 1s since offline apps ...
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