# 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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### Speeding up XMSS

To compute the XMSS Tree root, one needs to compute all the 2^h keys and hash them together. The higher the height of the tree, the more keys there are and the longer the KeyGen computation. The ...
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### Using hash of data as proof of integrity and preventing collision

Rather than storing user data when interacting with an app, I am storing the SHA3-256 of the data. This is because data storage in this particular environment is very limited. The data can be several ...
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### Cracking $f(x) = Cx \oplus Dx$

A program I reverse engineered is using $f(x) = Cx \oplus Dx$ where C = 0x20ef138e415 and D = 0xd3eafc3af14600 as a hash ...
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### PRNG For RSA (ANSI_X9.31)

I have a query please , I want to know how to generate random numbers using ANSI_X9.31 algorithm for RSA Algorithm please . Thank u
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### Help in understanding exactly how lattices are used as one-way functions for hashing

In my long-distance cryptography course, an assignment covers lattice-based cryptography. It is hard, and I am lost. There is no one to help me. Thus far, I have understood that: Lattices are a ...
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### Remote Attestation: when to use Checksum and when to use a Cryptographic Hash function?

In computer security applications, to check the integrity of a specific data/program binary, a cryptographic hash function is normally deployed to generate a digest and compare it with a reference ...
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### MD5 Collision Attack Explained

In one of my assignments, I came across this: Due to MD5’s length-extension behavior, we can append any suffix to both messages and know that the longer messages will also collide. This lets us ...
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### 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 ...
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### How is a group element converted into a key?

I've only just started research on cryptography so I apologize if this is a basic question or I'm getting terms confused. I'm researching braid group cryptography and currently looking at the Anshel-...
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### Is SHA-1 still practically secure under specific scenarios?

It is conjectured that SHA-1 has been broken from the "research" perspective, but not in the real world; that is, there exists an algebraic attack that explores weaknesses on its algebraic ...
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### Is there an efficient algorithm that allows to construct a cryptographically secure $n$-bit hash function based on two unkeyed $n$-bit permutations?

Let $f(x)$ and $g(x)$ denote two independent, “ideal”, unkeyed, public $n$-bit permutations (two publicly known bijective functions that produce $n$-bit outputs from $n$-bit inputs), where $n$ is an ...
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### Can someone please explain the “secret” and the “data” in the MD5 hashing algorithm?

I've been studying the MD5 hashing algorithm, and there is something that I just don't understand yet. They say that the server holds some sort or "secret" and that it appends some sort of &...
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### What are the algorithms used in Facebook's Diem algorithm?

Facebook plan a new cryptocurrency release called Diem. What algorithms are used? What output size is used for the hash function?
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### Hash function and operation commuting over composition

Is there a hash function $H$ and operation $\otimes$, which fulfill the following property? $$H(A) \otimes H(B) = H(A \otimes B)$$ $A$ and $B$ are two byte blocks of identical length, if necessary ...
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### Expandable hash function

I have been studying a cryptosystem using Mersenne primes. More specifically, this paper. I have implemented this cryptosystem in Python, but I am missing the key encapsulation system. On page 12, ...
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### Examples of post-quantum hash functions

We already know many examples of post-quantum cryptography for asymmetric, symmetric and digital signature algorithms, but is there any risk for hash functions to be attacked with quantum computers ...
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### Why do we use hex output for hash functions?

Why do we use hex representation as default for the output of a hash function's result? For example, the SHA-256 hash function: the output of SHA-256 in hex representation uses 64 characters, while ...
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### Are my calculations about WOTS parameters correct?

I'm reading the WOTS+ paper, but I'm having some trouble with its notation and specially the involved units. For example, under my interpretation, the parameters ...
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### CCA-Security Proof of a Particular Scheme

Suppose we have a scheme that works so: $\mathcal{P}_k =:\{P_k\colon \{0,1\}^{2n} \to \{0,1\}^{2n} \}$ is a strong PRP family. Encryption: $\operatorname{Enc}(k,m)=P_k(m\mathbin\Vert r)$, where $\Vert$...
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### HKDF Bit Security

I've always understood the bit security of hash functions to be related to their output size (eg. collision resistance). However, I recently came across a table from a Wickr blog post that lists HKDF-...
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### How to compose multiple values to MAC authenticate?

If the data I want to authenticate consists of multiple values and I compute a MAC simply concatenating the values, an adversary can "shift" characters within those values without ...
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### Making WOTS+ public keys shorter

In WOTS+ — as described in section 3 of RFC 8391 — public keys, private keys and signatures all consist of $len$ strings with $n$ bytes each, where $len, n \in \mathbb{N}$. Is it safe to use the hash ...
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### What are the properties of a hash function?

I have created a hash function. If I am asked whether it conforms to the definition of a hash function, I only know that it should have a fixed-size output. I use multiplication and adding of every ...