Cryptography Stack Exchange
Cryptography Stack Exchange

Questions tagged [randomness]

Usage of randomness (i.e. non-predictable data, usually in the form of bits or numbers) for cryptographic purposes.

For generating random numbers, see instead.

578 questions
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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 years. Some even believe that there is a…
Ozzah
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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 NSA... and knowing that PRNGs are important for…
Luc
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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 calculated in the general case?
this.josh
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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 ciphers which is fast? What is the difference…
randomness
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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 consequences if it is not? Examples of secure and…
agotsis
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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 themselves to do it. So, instead of simply…
K. B.
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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 dynamically generated using System.Random. Now, I know that System.Random is not really cryptographically random and should…
learnerX
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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 NIST had a trusted reputation. At first I thought…
user3461497
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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 identifier (be it an ID, user-name, or an Email…
GWLlosa
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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 first 5 ignoring the very first character and so on…
John T
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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 hex digits and call it good enough. I know that…
Paul
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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 that, given a sufficient quantity of output from an…
AJM
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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 has to be sufficiently random that guessing the…
aa8y
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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 openssl. Some questions: How low does entropy have to…
Brian Armstrong
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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 LavaRnd to seed srand(), then generate some big key…
Jacob H
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