Questions tagged [randomness]
Usage of randomness (i.e. non-predictable data, usually in the form of bits or numbers) for cryptographic purposes.
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Is modern encryption needlessly complicated?
RSA, DES, AES, etc., all use (relatively) complicated mathematics to encrypt some message with some key. For each of these methods, there have been several documented vulnerabilities found over the ...
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Technical feasibility of decrypting https by replacing the computer's PRNG
Intel has an on-chip RdRand function which supposedly bypasses the normally used entropy pool for /dev/urandom and directly injects output. Now rumors are going on that Intel works together with the ...
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What is entropy?
We discuss a lot of topics and use measures of entropy to determine how difficult it is for an attacker to be successful. What does entropy mean in the context of cryptography? How is entropy ...
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What is the difference between CSPRNG and PRNG?
What is the difference between CSPRNG and PRNG?
Is there performance differential between them? For example: We use PRNG for key generation which is very expensive and CSPRNG for IV/nonce in block ...
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What does it mean for a random number generator to be cryptographically secure?
I've never heard a good answer. I'd like to hear details about:
What are the criteria that make an RNG cryptographically secure?
Why must your RNG be cryptographically secure? I.e., what are the ...
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Why do some people believe that humans are "bad at" generating random numbers/characters like this?
I'm not even sure if they are serious, but I've heard many times that some people refuse to not only trust their computer to generate a random string (which is understandable) but also don't trust ...
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What is the practical impact of using System.Random which is not cryptographically random?
I recently noticed a .NET software using PBKDF to derive an encryption key from a password string. This password string was ...
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How useful is NIST's Randomness Beacon for cryptographic use?
NIST have just launched a new service called the NSANIST Randomness Beacon. It has been met with some initial skepticism. Perhaps the cryptography community would have used it before June 2013 when ...
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Necessity of Randomness of Salts?
Given the desire to have unique salts for each user of your system, is it actually necessary to create a cryptographically-random salt for each user?
If your system already has some other unique user ...
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Are the SHA family hash outputs practically random?
Say I hashed the output from a random number generator (with nonce), would the resulting SHA256 hash be as random as the inputted number?
And If I used the first 5 hex characters, and then used the ...
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How many hex digits do I need to compare when manually checking hash functions?
I sometimes run sha256sum on large files after transferring them from one place to another, and will just skim the hash output to verify it's correct. But, I usually just look at the first/last 5 or 6 ...
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A website that identifies an RNG from its output
This happened during a discussion of RNG entropy, and the difficulty of verifying the level of entropy in a long sequence of bits (e.g. a private key.)
A colleague of mine told me about a website ...
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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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Are one-time pads crackable in theory?
I've been taught that one-time pads are the only perfect encryption since the only way to recover the message is by knowing the key.
For example, for a target bitstring of 100 bits, I cannot scan all ...
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How can C rand() be exploited if a secure seed is used?
I've just started doing a research project on CSPRNGs and I would like to know what kind of vulnerabilities a regular PRNG has with a secure seed. For example, if I generate a random number using ...
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Examples of frauds discovered because someone tried to mimic a random sequence [closed]
[Moderator note: this question now lives there]
So, I'm preparing a talk about the well known fact that humans are bad at the task of generating uniformly random sequences of numbers when asked to do ...
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What to watch for with openssl generating weak keys? (low entropy)
(Disclaimer: I am regular software engineer with only basic crypto knowledge, so helpful if can be explained for a layman.)
I am concerned about generating weak keys on a shared linux box with ...
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How exactly is "true randomness" defined in the realms of cryptography?
Especially in relation to stream ciphers, I frequently read about (sometimes theoretical, sometimes practical) attacks that are able to "distinguish a ciphertext from a truly random stream".
What's ...
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Quality of randomness on a Linux system with haveged
Has anyone checked if using haveged, a Linux daemon which uses the HAVEGE algorithm, changes the non-deterministic properties of the random data from ...
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What is the difference between TRNG and CSPRNG?
I understand the output of a TRNG is almost impossible to reproduce, such a flipping a coin 100 times to produce a 100-bit sequence. However, it is also my understanding that a CSPRNG produces an ...
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What is the use of REAL random number generators in cryptography?
I understand the use of pseudo-random number generators. I am not getting mixed up between these and "real" random number generators.
However, I don't understand for what a real random number ...
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How random are commercial TRNGS
I'm thinking about buying a USB TRNG. How do I evaluate its randomness? I'm sure some are better than others but which is which? Are thermal-noise better than radio-noise TRNGs?
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Cracking a PRNG by observing ranks within groups of its output
Suppose that I am generating random numbers with Python's random module, so that there is a known random number generator (Mersenne Twister in this case). I've ...
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On Linux, does /dev/random unblocking imply that /dev/urandom is seeded?
Linux has the familiar problem that /dev/random blocks too much (insisting on being information-theoretically secure), while /dev/urandom doesn't block enough (it will return data before it's been ...
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How to best obtain bit sequences from throwing normal dice?
Throwing normal dice, one can get sequences of digits in [0,5]. In practice, which is the best procedure to transform such sequences into a desired number of bit ...
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Radioactive Decay, Gaussian or Uniform?
I'm trying to understand the nature of true randomness. I'm building an RNG using a radioactive source. Basically, I'm measuring the time between consecutive decays which in theory should be ...
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How to evaluate chi squared result?
I've been recently working on a (supposedly) TRNG. I'm still at the beginning of the project, so it is certainly not cryptographically secure yet, for now I'm just playing around. In fact, I've ...
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XOR a set of random numbers
Basic question about XOR and entropy - given a set $S$ of pseudo-random numbers in the range $[0,b]$, will XORing them produce a new pseudo-random number in $[0,b]$ or will the operation decrease the ...
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How does generating random numbers "remove entropy from your system"?
In a previous question, I quoted the --gen-random entry in the GPG Man Pages. At the end it says:
PLEASE, don’t use this command unless you know what you are ...
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How random is the shared secret in the Diffie Hellman key agreement
How random is the value $ZZ$ in the DH protocol?
This question was triggered by this somewhat naïve implementation in I2P shown by Sergei at Stackoverflow. Obviously $ZZ$ is distinguishable from a ...
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Why use randomness in digital signature algorithms?
I understand why randomness has to be employed in encryption, because deterministic ciphers are not IND-CPA. I don't understand why digital signature schemes that employ randomness, like RSA-PSS, are ...
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ElGamal Signature Scheme: Recovering the key when reusing randomness
Show how if Alice uses the same value of $k$ to sign two different messages $m_1$ and $m_2$, using the ElGamal signature scheme, Eve can recover the value of $a$ from the corresponding signatures $(...
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How to generate a list of unique random strings?
How would you generate a list of distinct random strings, where all strings are alphanumeric and have a fixed length?
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Is a die implemented in a physics engine truly random?
So, a fair die throw is really random, not pseudo. So, would a RNG implemented as the result of a die throw in a physics engine (say, Newton, Havok, Nvidia's PhysX) be regarded as both ...
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Does an encrypted random sequence conserve its "randomness"?
If you have a random uniform sequence of bits $A$ generated by a TRNG with good performance of randomness tests (eg Dieharder, NIST, Kolmogorov complexity, chi-square, etc) and perform an encryption (...
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Why are HOTP and TOTP implementations all using 6 digits and not more?
I was checking the RFC's after wondering for some time. In RFC 4226 - HOTP: An HMAC-Based One-Time Password Algorithm, it states on the appendix:
A simple enhancement in terms of security would be to ...
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Perfect shuffle possible with limited raw entropy?
I am trying to shuffle a standard 52-card deck in a perfect way (every outcome should be possible at an equal chance). I am not, at this point, concerned with cryptanalysis attacks against it.
I have ...
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Are poly1305 authenticators distinguishable from random data?
Assume Alice authenticates a message $M$ with nonce $N$ and secret key $K$, creating authenticator $A$. She then sends $A$ across the network.
The Poly1305 paper does not seem to specify whether it ...
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Why are MACs in general deterministic, whereas digital signature constructions are randomized?
The fact is I'm not quite sure if my question statement is true, however all the MAC constructions I know of (e.g. CBC-MAC, CMAC, HMAC) are deterministic, whereas many constructions for digital ...
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How are IVs used in association with RSA Encryption?
How are IVs used in association with RSA Encryption?
Can someone explain why we use them in this RSA context?
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Is there some way to generate a non-predictable random number in a decentralised network?
Is there a way to generate a random number with given restrictions:
It will be used in a decentralised network with a big number of peers (no central authority to generate it)
Its generation should ...
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Universally verifiable random beacon
I am developing a network where potentially many many nodes (billions, in principle?) should be able to agree on a random number. I would really prefer to avoid $O(N^2)$ procedures where everyone ...
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Algorithm: How to use x and y mouse movement co-ordinates to generate random data?
Background:
I'm making a program for fun as a learning exercise. I want to generate some actual random key material (not pseudorandom) from a JavaScript program. For my program is just for encrypting/...
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Why are $\lceil 1/\operatorname{entropy-per-bit} \rceil$ number of bits not sufficient to generate an unbiased bit?
Consider a biased RNG badrand() generating 1 with probability $0.9$ and 0 with probability $...
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Why do we require a CSPRNG's output to be indistinguishable from true random?
Everywhere I read, indistinguishability of output from true random is stated as a requirement for CSPRNGs. However nobody bothered to give the rationale for such a strong requirement.
Specifically, ...
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Why does TLS 1.3 use random-looking nonces for AEAD?
In TLS 1.3, it seems that nonces for AEAD are constructed by XORing the recorded sequence number with the server/client_write_IV (which is generated during the handshake). Thus, nonces are random-...
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Discrete Gaussian Sampling role in Lattice-Based Crypto?
I'm reading up on how post-quantum cryptography works, and stumbled upon the notion of discrete Gaussian sampling. However, I can't understand where it fits in the greater picture - currently it feels ...
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How to enhance randomness of AES?
I'm using PHP to encrypt a string and Java to decrypt it on a remote server. To perform the encryption, I'm using the strategy that can be found here.
My problem is that the strings I encrypt are ...
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How do you test randomness?
Suppose I receive a list of 1 million coinflips, and I want to know how likely it is that the list was randomly generated.
My first thought would be to count the number of heads and tails, which ...
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Better lower bound on min-entropy
In “Randomness Condensers for Efficiently Samplable,
Seed-Dependent Sources” by Dodis, Ristenpart, and Vadhan (PDF), I have seen the statement that:
any tuple of distributions $(X,Z)$ is $\...
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