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# Questions tagged [pseudo-random-function]

A pseudo-random function (PRF) is a family of deterministic functions indexed by a parameter, such that a randomly selected instance is computationally indistinguishable from a uniformly random function with the same input and output spaces.

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### Pseudorandom function of different keys

Could someone explain to me how they formulated the equation and how it equals to $0^{n}$ (like what F(x, x) equals to or how they cancel each other out?) on the first box and if its related to the ...
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### Pseudorandom function or not?

I've read Intro to Modern Cryptography PRF section (and example 3.26) and on stackexchange(1, 2), but I still don't fully know how to prove it (with probabilities) To prove it's a PRF, I know you ...
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### Number of possible functions for a PRP

In the Coursera crypto course, Dan Boneh states that if $F: K \times X \to Y$ is a PRF, if the size of the input space $X$ is $2^{128}$, and the size of the output space $Y$ is also $2^{128}$, then ...
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### Correlation among Psuedo Random Sequences generated from seeds which are correlated

I want to see and mathematically verify how PN sequence generated by LFSR or maximum length codes would correlate (auto-correlation and cross correlation) for seeds of varying correlation. Say I want ...
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### Secret-suffix MD5 as secure PRF (not MAC)

In standard secret-suffix fashion, assume we compute the PRF of some message $m$ as $MD5(x || k)$. Preneel and Van Oorschot showed in  that this secret-suffix method is unsatisfactory for ...
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### Why a pseudorandom permutation is used in a simulation based proof but pseudorandom function is not?

In this paper: https://eprint.iacr.org/2011/272.pdf the authors use peudorandom permutation in the protocols and proof rather than pseudorandom function. On page 31 (last two lines) they say: "We ...
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### Help with terms: hash function and a pseudorandom function

I am a little bit confused about the terms hash function and pseudorandom function. As far as I know, I can use a cryptographic strong hash function as a PRF. The hash function has a IV and is ...
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### Leaking information when a value is blinded

Assume all values are defined over a field $\mathbb{F}_p$ where $p$ is a large prime number. Given a fixed value $a,b$ we compute $v_i=a\cdot b+r_i$, where $r_i$ is picked uniformly at random from ...
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### Using only pseudorandom function to drive many deterministic keys

My question is related to: Can Pseudorandom values be used as secure keys? But here I'm only using pseudorandom function. Assume we have a pseudorandom function, $PRF$. We have a truly random ...
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### PHP predicting array_rand

Given the following PHP code (assuming PHP 5.6.x): ...
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### Relationship between source and output entropy

True Random Number Generator (TRNG) use external physical phenomena to generate true randomness. I have a TRNG which uses two sources (oscillators) and gives an output of 256 bits. The entropy of TRNG ...
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### Is there any pseudorandom function that outputs $n$ prime number of ring $Z_{N}$ where $N$ is Paillier public key

Let's assume $N$ is Paillier encryption public key, where $N=pq$ and $p,q$ are strong prime numbers. I have a set of plaintext $p_i$ whose domain is $N$. I want to deterministically generate a series ...
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### Is this a secure PRG or not?

I've seen this question! from 2 years ago: Given $F$ is a $PRF$, we define $G$ for an input $x\in\{0,1\}^n$ as follows: $$G(x) = F_k(x) \oplus F_k(x \oplus 1^s)$$ The question was if $G$ is a ...
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### Prove that the following MAC is insecure

I am trying to prove that the following MAC is insecure, but I don't know how to exploit the properties of the pseudorandom function $F$ involved: Gen generates a uniform $k \in \{0, 1\}^n$. To ...
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### Statistical tests for PRNG that generates a sequence which is not binary

Is there a pratical application to PRNG that generates a sequence which is not a binary one? A ternary, quaternary sequence, for instance. If so, how can we test this? Is there any alternative test ...
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### PRNG that takes input a $n$-bit string and gives output a $2n$-bit string?

Recently, I'm reading one paper of Boneh and Zhandry. They have mentioned a pseudo random number generator that takes input a $n$-bit string and gives a $2n$-bit string as output. They just used it as ...
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### How can I generate cryptographic-quality 1/f noise, aka “pink noise”?

Can anyone suggest how I'd generate cryptographic quality 1/f noise: aka 'pink noise', where the PSD follows 1/f. I'd be happy to derive the pink noise from white noise (e.g. /dev/urandom), but I ...
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### Combining multiple PRGs together

Got some theoretical questions about PRGs to solve (given by lecturer for self-learning, no score involved). Tried to find on the internet but couldn't figure out how to solve them, so I will mention ...
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### Collision-Resistance Hash Function PRF

I am trying to solve the following question with an example/proof. The question is from Introduction to Modern Cryptography by Katz and Lindell. Any help would be appreciated.
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### Simple application of verifiable random function?

I have been reading a little bit about verifiable random functions (e.g.). In the literature, these are described as "pseudo-random functions that provide a non-interactively verifiable proof for the ...
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### Can Pseudorandom values be used as secure keys?

I want to derive $n$ keys from a master key. I pick a master key $mk$ and use pseudo-random function (PRF) to generate $n$ pseudo-random values, $v_i=PRF(mk,i)$ where $1\leq i \leq n$. Next, I use ...
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### Key Derivation Function (KDF): Can a key derived from KDF be considered as a secure key?

Consider a case where we have a master key MS that is used in pseudo-random function to generate a set of pseudo-random values. Then we use key derivation function to derive a key from each of pseudo-...
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### secure PRF or not

I am new in Cryptography and I saw this question in a note I solved it but I'm not sure about my answers. Let $F : \{0, 1\}^n × \{0, 1\}^n→ \{0, 1\}^n$ be a secure PRF (i.e. a PRF where the key ...
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### Given PRNG $G(s)$, why is $G(s) || G(s+1)$ not a PRNG?

I have given a pseudorandom Generator $G(s)$, $|s|=n$ whose expansion $l(n)$ is $>2n$. I also know that $G^\prime(s) := G(s_1,\ldots,s_{\lfloor\frac{n}{2}\rfloor})$ is a pseudorandom generator. Now ...
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### Key derivation function in theory & practice

I am implementing a cryptographic protocol and I'd like to generate a set of seeds using a seed for a pseudo-random function. The reason is that I can pass on only one seed and it can be used to ...
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### Help with pseudorandom functions

I started a new lecture this year about crypto and I've had a few problems in the first few weeks with the exercises we got. I would appreciate a "guide" on how to solve problems like the following ...
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### If a PRG is constructed by iterating a PRF, is it backtracking-resistant?

Say we construct a pseudo-random generator from a pseudo-random function $f$ (using some constant key $k$ and some initial value $v_0$). We do this by feeding the output block of the PRF back into the ...