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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Does a practical collision attack on a cryptographic hash function also mean it fails “indistinguishable from random data”?

It is knowns that SHA-1 has been broken in practice using collision attacks. Related to SHA-1 this mainly had a negative impact on the security of Digital Certificate signatures Email PGP/GPG ...
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How to compute $a$ in the complex discard method of NIST SP 800-90

I've got a question about the complex discard method that has been specified in NIST SP 800-90, appendix A.5.2, steps: Use the random bit generator to generate a sequence of $m$ random bits, $(b_0, ...
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Are there flaws in (cryptographic) science/engineering/software/research due to pseudo random generators?

I am trying to see if there were any incidents in the past where using PRNG or not actual random scheme leaded to wrong conclusion in research. For example, a lot of fields today use simulations to ...
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Efficient way to combine collection of hashes into a single hash?

I have a system where each user will submit a set of data. The data will be hashed and their hash will be submitted to the server. My plan is to combine each users hash (converted to bytes XOR'd with ...
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Impact of the hash algorithm on a PRNG

Pseudorandom number generators often use hash functions for the generation. Some applications allow the users to choose this hash function, for example OpenVPN. From the OpenVPN manual: --prng alg ...
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3answers
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How can a system be non-deterministic?

Newbie here, so forgive me if this is a stupid question. In math class we learned about RSA encryption (as a practical application of what we learned about the Euler phi function and Fermats little ...
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Fuzzy Extractor for Binary Sequence

I was implementing Fuzzy Extractor on two close (noisy data). It's straight forward to use it to reconcile two close sets as per implementation given in https://www.cs.bu.edu/~reyzin/code/fuzzy.html, ...
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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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RIsk mitigation: block cypher vs xor

It sort of looks like to me that there is a kind of risk mitigation in the architecture of block cyphers vs the xor cypher. In XOR, the risk is entirely in the random number generator. The XOR ...
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Linear congruential generator with non constant increment

Consider this random generator function. A simplified version is provided below (this is C++, mind that "seed" is a reference): ...
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When is an RNG a CSPRNG, a CSRNG, or a TRNG?

In a recent answer to a question about CSPRNGs, it was stated that… Nondeterministic algorithms where there is no such requirement, and ideally could be replaced by a true random generator. Example: ...
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How to find breaking complexity of N bit sequence?

I do have a secret generation source with very low bit rate. In order to guarantee secrecy I need to wait till I have say 128 samples. How do I justify regarding brute force breaking in for $N$ bit ...
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1answer
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Value of $t$ in Fuzzy Exractor

Is there a defined method to choose value of $t$ when using fuzzy extractor to reconcile two close secrets? I did try with multiple values ranging from 5 to close to half of the sequence. I ...
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Does hashing a compromised rng and a secure rng give cryptographically secure random output?

If I have a compromised random source and a cryptographically secure one, is hashing them together makes a cryptographically secure random output? Example: The compromised random output: ABC The ...
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1answer
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Fortuna: With a Single Entropy Source

I have worked on a random number generator that has turned out to give results pretty close to those of Fortuna with a single source. I was wondering how it affects the performance and claims of ...
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Fortuna: Reseeding

It is recommended that a new seed file be generated approximately every ten minutes by seed file manager in FORTUNA,though it depends on the application and on the rate of the accumulation of entropy. ...
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1answer
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Fuzzy Extractor constructor for sequence reconciliation

The famous works on Fuzzy Extraction considers $set$ of inputs. I am interested in reconciliation for sequence of close data. Here order of elements are important unlike in previous one. Are there ...
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Fuzzy Extractor: Order of elements in set

Does order of elements in two sets matters to authenticate using Fuzzy Extractor? Using extractor as proposed in https://www.cs.bu.edu/~reyzin/fuzzy.html it seems the set difference is zero for this ...
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Creating a k bit random string

My goal is to create a random $k$ bit string. My question can be divided in two parts. If a $n$ bit string $s$ is computationally indistinguishable from a random $n$ bit string, can we say that the ...
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What are the dangers of using CPU clock drift for generating random data?

From what I understand, a physical source of true randomness could be achieved with a multi-core processor, by using clock drift between two or more cores. However, a processor is easier to ...
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How much entropy do you need for a secure certificate generation?

So in OpenSSL you have the -engine tag for inputting your own entropy as a source for generating whatever. So if you wanted to generate a 2048-bit RSA certificate ...
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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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1answer
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Attacks on Biased OTP

I know that a perfectly random unbiased and not reused OTP cipher is perfect. An OTP under cryptanalysis has a very strong bias (up to 30 % of symbols are represented by 5 out of 255 possible symbols) ...
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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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Perfect Secrecy with 1 Time Complex Secret Cypher

Is it possible to achieve perfect secrecy, unbreakable, unguessable, uncrackable by using a totally secret cypher? The following conditions must apply: Using the secret cypher only 1 time, so that ...
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Generate random numbers whose sum is equal to a constant value modulo n

I want to generate $n$ random numbers $u_i \in [ 0, 2^{\kappa + 1})$ such that $\sum u_i = c$ $mod$ $2^{\kappa + 1} $, where c is a constant. Also, taking $n - 1$ random numbers and subtracting their ...
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Hardware random number generator for lottery?

To be able to generate random numbers for lottery games, we have the following requirement: The random number generator, which uses the deterministic algorithm to determine the game result, has to ...
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Does the size of a file influence the randomness if used as random input?

(I am a cypto amatuer ) So in Openssl there is the "-rand" option for taking a file containing randomness for the RNG . So I thought taking a pretty big file would make it more secure . So if you ...
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1answer
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Pseudo-random generator explanation by Bruce Schneier

I am reading about Pseudo-Random Sequences in Applied Cryptography book by Bruce Schneier. Description is provided below. A pseudo-random sequence is one that looks random. The sequence's period ...
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Difference between public coin and common coin?

What is the difference between public coin and a common coin? I often see both appearing in the literature, but I cannot explain myself, whether they are the same concept or not.
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Where do key generation algorithms take the randomness from?

I was just wondering, because in many encryption tools like Veracrypt or GnuPG you have to generate pseudo randomness with your mouse movement. So, where do automatically generated keys take that ...
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1answer
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Definition of randomly generate in the parallelepiped

I am reading the [CLT13] paper regarding multilinear maps over the integers and I have some troubles in understanding what the following random generation means: The vectors of the matrix $r_i \in \...
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Why does a Hashing Function produce good Random Numbers if Input is random?

I've heard about using a hash approach to create random numbers based on two independent entropy sources A, B: $h_{i} = H(a_i+b_i)$ $H$ could be for instance SHA-1, or SHA-256. My questions are: 1)...
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Lsb as hard core predicate in a sign-hash scheme

Given a random oracle and a deterministic signature scheme. Is the following $hc(x)$ an hardcore predicate of $H(SIG_k(x))$ ? $$hc(x)=lsb(H(SIG_k(x)))$$ How would I get to think about this? I saw a ...
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1answer
287 views

Sub exponentially hard OWF , PRF and iO

I'm currently reading the work "Obfuscation of probabilistic circuits and Applications' by Canetti Lin Tessaro and Vaikuntanathan 2015. It says sub exponentially hard OWF implies sub exponentially ...
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2answers
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Does Benford's law hold against encrypted data?

If I can assume that the output of a block cipher like AES is a PRandom distribution, can I assume that Benford's law will hold if I partition that output into integer data?
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1answer
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Can a random permutation be restored / decrypted?

Say you have a 1,000,000 random bytes file and you split it into 1000 x (1000 bytes) pieces. You then pick two random pieces and swap them writing down the position of the pieces (eg. swapped piece ...
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728 views

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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0answers
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Relationship between "Entropy" and "Security" in crypto functions

There is a lot of confusion between "entropy" and "security" of a cryptographic function. I like to visualize it as the entropy being the water, and the crypto function being a glass. So for ...
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Does RSA_PRBG security depend on keeping seed secret?

The HAC provides a PRBG using RSA (Chapter 5 p.185): It appears the seed must be kept secret if $e$ is a well known value. If $e$ is uniformly distributed between 1 and $\phi$, then the seed does not ...
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ISO 9564-1 format 4: do I need an IV?

ISO 9564-1 format 4 describes an extended PIN block format. Simply said, this standard can be used to encrypt 4-digit PIN codes in a secure way. The standard mentions (simplified) to add random ...
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Is the number still a CSPRN if we only allow an interval from a CSPRNG?

tr -dc 0-9 < /dev/urandom | fold -w 3 | awk '$0>=100 && $0<=200' What this line does: /dev/urandom (Linux) is proven to be a CSPRNG, that is ...
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1answer
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Can physical object hiding be quantified with entropy?

If it works in the virtual world, why can't the same principle work in the real world? For example if you want to hide a private key, you need a virtual haystack to hide it inside, which is the ...
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Can a repeated random sequence be considered random?

Imagine I have a 1000000 bit sequence that is considered random ( ie the output of a TRNG). Now imagine I 'double' that sequence : I concatenate the same sequence 2 times : " my 1000000 bits "concat"...
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Is it safe to encode an entropy this way?

I have been analyzing the source code of a software, and I came across this encoding snippet, I would like to know if it's safe to encode an entropy source this way. So the entropy source is a 132bit ...
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3answers
561 views

How much original entropy is lost if a part of the hash is known?

You have an entropy source of n bits You hash it with SHA-512 for example k bits of the SHA-512 output are publicly revealed, ...
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1answer
342 views

How much entropy is lost if 1 character is fixed in HMAC SHA-512?

We have an entropy source called “Entropy”. We encode this entropy with HMAC-SHA512 using a “Key”. The Key is public, but the Entropy is secret. We are then testing for the HMAC-SHA512 output in order ...
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1answer
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Hashing entropy to generate 256bit key?

I have a 256bit fully random entropy source from dices, which is probably not cryptographically secure. I have read that it's customary to take the hash of the entropy source in order to generate a ...
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Is a large random number cryptographically equivalent to the product of multiple smaller ones?

Say I create a 256-bit key by taking a random number between $0$ and $2^{256}-1$. Would it be cryptographically equivalent to generate $8$ numbers $r_1\dots r_8$ between $0$ and $31$, and combining ...
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How can I extract randomness from a JPEG file?

In a previous question I asked if (and why) BlueRand can or cannot be considered as a TRNG. Established that it's not a TRNG (due to the reasons explained by some users in the previous question), ...

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