# 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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### Is this PRG secure?

$G$ is a secure PRG in range $\{0,1\}^n\rightarrow\{0,1\}^{n+1}$. Let us define $G'(S)=G(S\oplus G(S)_{1,...,n})$, s.t. $G(S)_{1,...,n}$ is the first n bits of $G(S)$. Is $G'(S)$ a secure PRG? ...
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### How can we formally define a Pseudo-Random Shuffle function?

My question is related to: When we turn Random shuffle to Pseudorandom Shuffle The idea is to permute the elements in vector $\mathbf{v}$ pseudorandomly, where $|\mathbf{v}|=n$; I am aware that we ...
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### Is $f(g)$ a PRG if $f$ is a OWF and $g$ a PRG?

If we have a PRG $g$ and a OWF $f$, can we say that $g' = f(g)$ is a PRG? And what if $g$ stretches its input by a factor of 2?
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### Would the result of encrypting weak random data via AES-128 with a CSPRNG-generated key be considered strong/secure random data?

I am trying to understand the security implications of using a well known block (or stream but in this example block) cipher like AES-128 to produce pseudo-random data. My specific question is would ...
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### Alternative AES key expansion for CTR based random number generator

Daniel J. Bernstein proposes an alternative to NIST AES-CTR based deterministic random number generator (AES-CTR-DRBG). Instead of a less performant complex construction, he uses an standard AES-CRT ...
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### Dependence of a Pseudorandom Function's Security on its Input/Output Spaces

Let $n$ be a security parameter and $F:\{0,1\}^{\ell_{key}(n)} \times \{0,1\}^{\ell_{in}(n)} \rightarrow \{0,1\}^{\ell_{out}(n)}$ be a keyed function which forms a family of Pseudorandom Functions (...
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### Construction PRF from PRG

As discussed here, a classic and secure construction of PRF from PRG is: $F_k(x_1x_2\cdots x_n) = G_{x_n}(\cdots(G_{x_2}(G_{x_1}(k)))\cdots)$ where $G$ is a secure pseudorandom generator. I was ...
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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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### 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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### 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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### Is it possible to compute permutations of a sequence of bytes by using exactly one pseudo-random number?

Suppose I have a certain sequence of bytes, for example 0102F4829hex, and I can pick from a pseudo-random number generator exactly one number. Is it possible, by using exactly one pseudo-random number ...