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Questions tagged [pseudo-random-generator]

In cryptography, a pseudo-random generator (PRG) is a deterministic procedure that maps a random seed to a longer pseudo-random string such that no statistical test can distinguish between the output of the generator and the uniform distribution. Pseudo-random generators have numerous applications in cryptography. For instance, pseudo-random generators provide an efficient analog of one-time pads.

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How to make a hypothesis test for a simple statistical test for a certain RNG?

I'm self-studying about hypothesis test in the context of RNGs. I'm building a hypothesis test from scratch. I'm taking the simplest statistical test I can think of: how many $1$s are there in the ...
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What SALT value will be used in HKDF_EXTRACT in TLS1.3?

What SALT value will be used in HKDF_EXTRACT while generating the Handshake Secret (when there will not be any PSK)?
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36 views

Showing the non-pseudorandomness of a generator

I'm sorry if this question is too novice. It comes from a practice midterm in a cryptography course which I'm taking, and my confusion here is really that I don't know the "tools" that one uses in ...
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1answer
78 views

Formal definition PRNG

I tried to look for a book that presents cryptographic concepts(specially PRNG) in a formal way but what I find is an intuitive approach. So my question is what is the formal definition of Psuedo-...
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Which 'info' and 'salt' parameters to use in HKDF for TLS 1.3?

all the following discussion is for HKDF in TLS1.3: Regarding the 'salt' parameter in - HKDF-Extract(salt, IKM) as written in RFC 5869: HKDF without having to protect the secrecy of the salt. In ...
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73 views

How many bits needed for the LFSR to generate a specific number of sequences

I need to generate 64bit data sequences for 16 times pseudo randomly. How many bits should the linear feedback shift register have to be able to do so? I mean what is the number of bits for the ...
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122 views

Golomb's Randomness postulates

In Handbook of applied cryptography, Golomb's randomness postulates are given: Let $s$ be a periodic sequence of period $N$. Golomb’s randomness postulates are the following. R1: In the cycle $s_N$ ...
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show that G' is not a secure PRG even if G is

Hello I'm trying to show that the function G'(s) = G(s) || G(G(s)) is not a secure PRG even if G is. My first question is that in this case, how do I know what G ...
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Using a hash function as a random number generator

Using MD5 or SHA1 for instance, and applying integers (as seed so to speak) to the hash function, in sequence, and only keeping, say, the first 64 bits of the resulting hash, do we always have a ...
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1answer
80 views

A modification of the Blum-Micalli construction

Consider the following modification of the Blum-Micalli construction (denoted by BM): $G_l(x) = f^l(x) || BM^l(x)$ I am asked the following questions about it: Show it is a PRG of fixed stretch ...
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Does ChaCha20-Poly1305 need random nonce?

RFC 7539 says: A 96-bit nonce -- different for each invocation with the same key It doesn't explicitly say whether it has to be random or not. If we use an ever incrementing counter. Would that be ...
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Pseudorandomness based on homomorphic multiplication property of Paillier cryptosystem

Given the instance $(n, g, \lambda)$ of Paillier cryptosystem with $\text{ord}(g) = n \lambda$ (symbols have their usual meaning), and $c = g^{na}$, is it possible to distinguish (computationally) $c' ...
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Using Tweets as a Random seed

I would like to start by saying I know nothing about Cryptography and was reading up on how to choose a random seed and this link is something that I found. What I basically understood that the seed ...
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1answer
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Is this MAC correct and secure?

Let $m \in \{0, 1\}^{2n} = m_1 || m_2$. Let's also assume that $F_k$ is a PRF and $G$ is a PRG defined as $G: \{0, 1\}^n \rightarrow \{0, 1\}^n$. Now, Let's define the $MAC$ scheme as follows: $$MAC(...
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1answer
137 views

Is PRG On Concatenation of Input a PRG

This is a homework assignment, so I'm not expecting full solutions, just general guidance. Let a PRG $G:\left\{ 0,1\right\} ^{n}\to\left\{ 0,1\right\} ^{l\left(n\right)}$ (where $l\left(n\right)$ ...
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Indistinguishable encryptions and CPA-secure example

Let $ F $ be a PRF and $ G$ be a PRG with expansion factor $n \to n +1 $ For the following encryption scheme, decide whether it has indistinguishable encryptions and whether it is CPA-secure. ...
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Never design your own crypto…how to design a PRG

As a new learner of cryptography I have learnt from online tutorials and lectures not to design your own crypto. What I am trying to understand is the fundamental to designing PRGs to a given context ...
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Calculating t and epsilon for a computationally indistinguishable pseudo random generator

I have a PRG $G : \{0, 1\}^n \rightarrow \{0, 1\}^{2n}$. How would you go about calculating the optimal size of $n$ given that you have $$\epsilon = \cfrac{1}{2^{80}}$$ and, $t = 2$ years for a ...
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198 views

Stronger security definition of PRG

By the standard security definition of a Pseudo Random Generator, if $G$ is a PRG, then $G'$ such that $G'(0\mathbin\|x)=0\mathbin\|G(x)$ and $G'(1\mathbin\|x)=1\mathbin\|G(x)$ is a PRG. We can build ...
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PRG Theory Design

PRG theory design is something of interest to me at the moment in the security of cryptography. I am interested in learning how to come with PRGs for random functions such as $\{0,1\}^{2n} \...
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1answer
128 views

Pseudorandom generator designs

When designing pseudorandom generators what should one consider? Here is an example pseudorandom generator $F^t : \{0,1\}^n \rightarrow \{0,1\}^{4n}$. I have no idea what it means, so what does it ...
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1answer
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PRGs exist if computationally secret encryption schemes exist

I have understood the "equivalences" between PRP, PRF and PRG. Now, I just read an statement in my lecture notes that made me think that there has to be a conversion between PRG and computationally ...
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$G_f(x) = x \|f(x)$ is not a PRG with $\operatorname{DPT}$-computable function $f$

Let $f:\{0,1\}^* \rightarrow \{0,1\}$ be any $\operatorname{DPT}$-computable function. Show that $G_f(x) = x \|f(x)$ is not a PRG. Can anyone help me on understand how to prove this?
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1answer
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Cryptography Pseudo Random Generator example question - proof

For ii) G2 was proven to be a PRG, and it seems the solution for G5 uses G2. Can someone try and explain to me the solution that I was given? I specially do not understand how to calculate the given ...
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1answer
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What's the internal state size and output range of mrg32k3a?

This is Pierre L'Ecuyer's PRNG. I know its period is $2^{191}$, but I don't know what is its internal state size. What is it?
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Oracle version of the IND-PRG game with q queries

Consider the following oracle-based game: $O_0$: Init: $1^n$; Query: output $y \stackrel{u}{\in} \{0,1\}^{l(n)}$ $O_1$: Init: $1^n$; Query: output $G(x)$ with $x \stackrel{u}{\in} \{0,1\}^{n}...
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Can we construct a PRF directly from a one way permutation function?

In Introduction to Modern Cryptography first a pseudo random generator (PRG) is constructed from a one way function (OWF). After that the PRG is used to to construct pseudorandom functions (PRF). Is ...
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2answers
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Is this test result sufficient to steer clear from this RNG for cryptographic applications?

I'm not really interested in this PRNG. I'm more interested in understanding what it takes to fail the security threshold for cryptographic applications. I'm taking the C PRNG as an example. ...
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132 views

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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2answers
205 views

Does there exist a CSPRNG that does not require generating prime numbers, but also does not depend on any other cryptographic primitives?

The following excerpt is taken from the “Cryptographically secure pseudorandom number generator” article on Wikipedia: CSPRNG designs are divided into three classes: those based on ...
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1answer
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Making PRNG cryptographically secure thru shuffling?

Is it practical to make a PRNG cryptographically secure if I shuffle the randomly generated numbers (say 256-bit) several times before hashing it, even if a hacker knows when I generate the numbers? ...
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1answer
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Problems understanding the applications of pseudo random number generators

I am trying to explore different methods used to generate pseudo-random numbers for my project in maths and I would be very grateful for some help or references to valuable sources as it is very hard ...
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1answer
746 views

What does “seed” mean in cryptography?

I have come across "seed" many times, and at each time, it confuses me more and more. I think it has a well-known meaning in cryptography, so what is it? They can usually use the limited number of ...
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1answer
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Instead of sending a set of random values, send a key for a PRF

Some Protocols require one party to send $n$ random challenges (or random values) to another party. For communication efficiency purpose, one can pick a random key for a pseudorandom function, and ...
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1answer
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Can there be a PRG $G(x)$ where at most half the output bits are 1?

Can there exist a pseduorandom generator, $G(x)$, with input length $|x|=n$ and output length $|G(x)|=2n$, where $\leq n$ bits of $G(x)$ are equal to 1 for every possible input $x$? (I.e. no more than ...
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1answer
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If $G$ is a PRG, is $F(s)=G(S)||G(\bar{s})$ necessarily a PRG?

Let $G$ be a pseudorandom generator, and $F(s)=G(s)||G(\bar{s})$ (where $\bar{s}$ denotes the bitwise complement of $s$), is $F$ necessarily a PRG? My intuition says that it is a PRG, as clearly $G(s)...
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1answer
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Attack of the Middle Square Weyl Sequence PRNG

The Middle Square Weyl Sequence PRNG was proposed as illustration of properties of CSPRNGs in this answer (now deleted). This PRNG was introduced (without claim of cryptographic security) by Bernard ...
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How fast does a pseudorandom number generator have to be in order to be competitive?

Let $\{x_n\}_{n}$ be the pseudorandom sequence produced by a cryptographically secure pseudorandom number generator $G$. What is the cost of computing a term in the sequence for a competitive ...
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1answer
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Pseudo-random generators and pitfalls

I've read the Chapter "Randomness" from the Serious Cryptography book and it raised some questions. Namely: It is written that Mersenne Twister is proved to be cryptographically irreliable. And that ...
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1answer
117 views

Does hashing a PRNG by a cryptographically secure hashing algorithm result in a CSPRNG?

Or specifically, does ChaCha20 hashing of the xoroshiro128+ random number generator result in a cryptographically secure random number generator?
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286 views

Is a one-way function pseudorandom?

For one-way function $f$ I understand that $g(x)=0^{n}\mathbin\|f(x)$ is a one- way function with respect to $2n$, where there is $n$ bits of $0$ in the beginning and the output of $f$ in the second ...
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Mersenne Twister's vulnerabilty with small-size distributions

C++ rookie here, trying to wrap his head around (CS)PRNGs. I (assume that I) already understand the concept of the Mersenne Twister being "broken" (i.e. not cryptographically secure) due to its ...
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1answer
170 views

Is the XOR of PRGs sharing the same input a PRG?

I have question in learning PRG. Given that $f$ and $f_1$ are PRGs, both $\{0,1\}^n \to \{0,1\}^{2n}$. Is $g(x) = f(x)$ xor $f_1(x)$ a PRG? Someone told me that in this case, $g(x)$ is not a PRG, ...
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1answer
104 views

Oblivious Encryption: Oblivious Transfer Based Encryption

I’m aware of a couple of OT protocols, most of which use Public Key Cryptography, Key Establishment (or similar constructs) as the base. I don’t really have specific knowledge on other OT protocols, ...
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1answer
265 views

PRNG with a truly random seed?

PRNG (Wikipedia): "The PRNG-generated sequence is not truly random, because it is completely determined by an initial value, called the PRNG's seed (which may include truly random values)." My ...
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Inversive Congruential Generator

The inversive congruential generator over the prime field $k=Z/pZ$ is given by the iterations of the map $x\mapsto a/x+b$ if $x\neq 0$ or $b$ if $x=0$. One can choose $a,b$ in $k$ such that the orbit ...
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How is a ciphertext encrypted using random numbers decrypted using a symmetric key algorithm

We use true random number generators as a source of keys for encryption. What I can not wrap my head around is: How is this cipher text decrypted in case of symmetric key algorithm as we need the same ...
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1answer
111 views

repeatedly hashing result and using reverse sequence as RNG secure?

I want to have a source of randomness for which: no one but me can predict the next number in the sequence. I know the entire sequence in advance, but I have no way of manipulating it once the first ...
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1answer
76 views

Expected Linear Complexity of a sequence

Let (s) be a sequence of length n. What are the expected linear complexities of (s) and $(s)^{\infty}$ (meaning that the periodic version of s)? I have no idea of the answer to this question? What ...