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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Does a regularly reseeded PRNG provide backtracking resistance?
I'm currently discussing a security topic with some of my classmates.
A cryptographic PRNG typically provides backtracking resistance if an adversary that compromises the internal PRNG state cannot ...
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0answers
45 views
Simple but secure hand cipher for a computerless world [closed]
this is my first time posting here, so please be gentle! As may be obvious, I'm an amateur who knows very little cryptanalysis.
The goal
I've been playing around trying to make a simple but strong-...
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1answer
57 views
Why is LCG PRNG chosen to be as c++ rand() function?
The C++ rand() function is an Linear Congruential Generator (LCG) PRNG. my questions are:
Why was this algorithm chosen?
What are the pros and cons?
Is it good for cryptography?
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1answer
64 views
How to symmetrically encrypt 64bit values?
I'm curious about an algorithm that would be good for the following scenario:
32-bit "plaintext" input, taken from a counter
32 or 64-bit "ciphertext" output
It should be possible to decrypt the ...
2
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1answer
77 views
Constructions of PRF (Pseudo Random Function)
I was taught only GGM based PRF construction in class. It's very inefficient. I am just curious about various PRF constructions from standard assumptions. Please provide a few PRF constructions from ...
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2answers
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Meaning of epsilon in proving a PRG is predictable/ un predictable
I am quite confused, I have been following a course on crypto provided by Dan Boneh, this is the lecture I am confused with - https://www.youtube.com/watch?v=EjWap3szsPk time stamp 8:58 - 11:00
I don'...
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2answers
85 views
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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1answer
44 views
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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1answer
40 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 ...
2
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1answer
84 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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0answers
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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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0answers
105 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 ...
3
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1answer
154 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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0answers
140 views
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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2answers
1k views
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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1answer
258 views
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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0answers
32 views
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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4answers
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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
82 views
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:
$$MAC(...
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1answer
199 views
Is PRG On Concatenation of Input a PRG
This is a homework assignment, so I'm not expecting full solutions, just general guidance.
Let a PRG $G:\left\{ 0,1\right\} ^{n}\to\left\{ 0,1\right\} ^{l\left(n\right)}$ (where $l\left(n\right)$ ...
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0answers
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Indistinguishable encryptions and CPA-secure example
Let $ F $ be a PRF and $ G$ be a PRG with expansion factor $n \to n +1 $ For the following encryption scheme, decide whether it has indistinguishable encryptions and whether it is CPA-secure.
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0answers
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Never design your own crypto…how to design a PRG
As a new learner of cryptography I have learnt from online tutorials and lectures not to design your own crypto.
What I am trying to understand is the fundamental to designing PRGs to a given context ...
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0answers
104 views
Calculating t and epsilon for a computationally indistinguishable pseudo random generator
I have a PRG $G : \{0, 1\}^n \rightarrow \{0, 1\}^{2n}$.
How would you go about calculating the optimal size of $n$ given that you have
$$\epsilon = \cfrac{1}{2^{80}}$$
and, $t = 2$ years for a ...
4
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1answer
202 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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1answer
77 views
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
132 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
58 views
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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0answers
83 views
$G_f(x) = x \|f(x)$ 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
142 views
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 ...
2
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1answer
49 views
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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0answers
84 views
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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0answers
147 views
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
1k views
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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2answers
135 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
217 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 ...
2
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1answer
121 views
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?
...
2
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1answer
152 views
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
788 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
48 views
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
103 views
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
273 views
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
283 views
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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2answers
770 views
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
87 views
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 ...
0
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1answer
128 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?
4
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1answer
313 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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0answers
58 views
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 ...
2
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1answer
186 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
120 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, ...
