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Questions tagged [entropy]

In computing, entropy is the randomness collected by an operating system or application for use in cryptography or other uses that require random data. This randomness is often collected from hardware sources, either pre-existing ones such as mouse movements or specially provided randomness generators.

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How to generate high entropy from physical sources?

What could be the main sources for strong noise generation for an AVR128DA64, so that the obtained entropy approaches or even equals 128 bits? I'm interested in good sources of physical entropy.
Hanna's user avatar
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14 votes
4 answers
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Security of a non-random password but that relies on information an attacker cannot possibly know

I am trying to figure out whether a non-random password that relies on information an attacker cannot possibly know can be secure. To give an example, let’s say that I generate my password by putting ...
hb20007's user avatar
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7 votes
4 answers
9k views

Is a randomly generated 80-bit password strong enough nowadays?

Theoretical question - Say we have a randomly generated password with 80-bit entropy, stored as a single-round, unsalted SHA256 hash. For a determined attacker with current (2024) technology, what ...
user13525's user avatar
2 votes
0 answers
110 views

Why does Bluetooth Low Energy Secure Connections with Passkey Entry check the Passkey bit by bit?

If we want to enable an authenticated connection via BLE the passkey method seems like a good idea. A 6-digit PIN is generated randomly on one device and has to be entered on the other - these 20 Bit ...
jusaca's user avatar
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2 answers
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XKCD #936 Why not both?

This "correct horse battery staple" XKCD comic #936 was a topic discussed here already. However, I saw no one suggesting combining the second method of using dictionary words with an "...
CrazyMan's user avatar
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176 views

How does user activity affect entropy generation process in GnuPG?

Earlier today, I was using gpg to generate keys for work. While doing so, I noticed: We need to generate a lot of random bytes. It is a good idea to perform some other action (type on the keyboard, ...
Rahul Dixit's user avatar
0 votes
2 answers
188 views

Is there any good way of calculating a brain-generated password's entropy?

After reading this post, I understand that a password's entropy depends on the assumptions made when it is to be attacked (e.g. if it is generated randomly from a list of 2048 words, etc.). Let's ...
Dan's user avatar
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2 votes
2 answers
225 views

Why do entropies of passwords significantly differ from site to site?

I read the infamous xkcd cartoon comparing two passwords and their strength. Curious whether their calculation was accurate, I searched many entropy calculators and plugged in the two examples from ...
xk58945's user avatar
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3 answers
200 views

How to analyze the security of a custom passphrase?

Let's assume person A chooses 15 words for a passphrase with an average length of 5. The passphrase meets following conditions. Word conditions: The first word is not a valid word and can't be found ...
127 001's user avatar
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-1 votes
1 answer
285 views

How can you calculate the entropy of arbitrary password rules with known distributions? [duplicate]

Many online entropy calculators make certain assumptions (like assuming a password is as rare as the set of random characters that will generate it), or handwave away the math. I want to know how to ...
Atomic Tripod's user avatar
10 votes
6 answers
6k views

What is the best way to calculate true password entropy for human created passwords?

Okay, I know it might seem this has already been beaten to death but, hear me out. I am including a fairly good password strength algorithm for my app for users on sign-up. This one, which I've copied ...
RobbB's user avatar
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1 answer
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Why does some Ransomware encrypt also the file header and trailer?

Some time ago I read an article that mentioned that it is possible for some ransomware to change the magic numbers of a file (that makes sense). However, the authors claimed that their method was ...
Moooz's user avatar
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25 votes
6 answers
9k views

Is a sha256 hash of a unix timestamp a strong password

I am setting up a postgres db that will never be used by humans. In fact, I really don't need to know it myself ever. I assumed that just using a 256bit(64 alphanumeric chars) hash of a unix timestamp ...
ThisGuyCantEven's user avatar
1 vote
0 answers
132 views

Comparing HAVEGE and Jitter Entropy algorithms

How does the HAVEGE method (or rather, the specific adaption of it as used in haveged) for generating randomness from timing differ from that of the Jitter Entropy method? Is there any research ...
forest's user avatar
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2 votes
2 answers
175 views

Rationale behind disallowing the use of similar passwords?

I recently had to change my password on a linux server (RedHat). It wouldn't let me use my password of choice because it was "too similar" to my previous password. Is this really ...
Huliax's user avatar
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1 answer
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Should I be concerned if a website has password restrictions that reduce complexity?

Chase banking has two odd restrictions on their accepted passwords. Passwords have a maximum length of 32 characters Passwords can not contain special characters or punctuation I am a software ...
Tarynn's user avatar
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9 votes
2 answers
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How many bits of entropy should a password have to be reasonably future proof (10+ years)?

I’ve seen estimations that the NSA is capable of at least 1 trillion (PGP pass phrase) guesses per second, which would mean a password with 80 bits of entropy would take, on average, over 15,000 years ...
abyssalarcanist's user avatar
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What is the entropy of a password made from the initial letters from an English sentence [duplicate]

One way to build a password is to take the first letter from each word in a sentence. For example, the password "Itsfrqbtwaawwnsl" comes from the sentence "I tried searching for related ...
hugomg's user avatar
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0 answers
198 views

How much entropy is needed for encrypting data locally?

I understand that, when storing data on the cloud or something else that might get leaked to the public, the security margin should be at least 128 bit, 256 bit should be used for data that should ...
Gamer2015's user avatar
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1 answer
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Are weak entropy sources worth it?

I maintain an operating system that can be deployed to embedded devices with highly diverse capabilities. One of the aspects of porting the OS to a device is declaring the available entropy sources (...
Gilles 'SO- stop being evil''s user avatar
2 votes
5 answers
1k views

Attacks Relying on Poor Entropy

I'm creating a quantum random number generator as part of my thesis. As part of the research phase, I'm trying to substantiate my aspertion that encryption is significantly weakened if a computer ...
ScottishTapWater's user avatar
1 vote
1 answer
178 views

Does a TPM replace the default device's security, or add to it?

Does a TPM replace the default device's security, or add to it? I will try to re formulate it into 2 questions, just to explain what my question is, since I am not very good at English writing. If we ...
William Martens's user avatar
20 votes
6 answers
7k views

Why use entropy at all in considering password strength?

I don’t understand the password vs. passphrase analyses that I read. Let me explain. Here is a pass phrase. It has 5 words using only lower case (I’m ignoring randomness for this purpose): friend ...
Steven Graeber's user avatar
1 vote
1 answer
439 views

Feeding entropy pool with my own data [duplicate]

Let's state that I have a huge bunch of truly unpredictable random data in file "random.bin". The random data has been created outside of my system and has been securely transfered into my ...
Algiz's user avatar
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1 answer
744 views

Security of PHP's str_shuffle()

I'm doing some research on PHP's str_shuffle function, I already asked this question multiply times on StackOverflow but got no answer https://stackoverflow.com/questions/61968859/is-it-possible-to-...
user239146's user avatar
4 votes
1 answer
5k views

Chance of guessing any valid credit card data

What's the chance of guessing valid credit card data that could be used to make a payment online? To me, it looks like it's not extremely hard to guess, but I'm not able to calculate the probability. ...
reed's user avatar
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8 votes
2 answers
353 views

Randomly selected words converted into sentence. Did I lose passphrase strength or gain it?

I got 5 dice and opened EFF's wordlist, and generated a random five-word passphrase (all letters small with spaces, no punctuation) for my PC. The words were making up a meaningful scene in my mind, ...
user's user avatar
  • 275
5 votes
2 answers
4k views

Is it cryptographically safe to use veracrypt in a virtualbox virtual machine?

Does virtualbox provide enough entropy (random numbers) for the veracrypt program on the virtual machine? Is it cryptographically safe to use veracrypt inside a virtualbox in a windows 10 guest?
chanaccll's user avatar
2 votes
1 answer
339 views

How long does a secret URL need to be?

I'm currently creating a small service where users can upload images (just a free time project). The images are either private, public (unlisted) or public (listed). Now I'm wondering for public ...
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7 votes
5 answers
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Specific character based policy for passwords

I'm wondering, would it be clearer to declare a company wide requirement with regard to password theoretical entropy, rather than the usual "at least one big letter, and a small latter, and special ...
Woodstock's user avatar
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0 votes
1 answer
151 views

Limiting number of combo attempts with Fail2ban and 128 bits of entropy

Apps such as Fail2ban and DenyHosts enable unix administrators to limit username/password combo attempts to typically 3 attempts. But why 3? Some admins enable more, like 6 or 8 giving honest users a ...
enoren5's user avatar
  • 111
1 vote
1 answer
149 views

What affect does modulus have on CSPRNG outputs?

I work in security and I've seen modulus (modulo) used in many encoding and crypto algorithms. However, today, a friend of mine mentioned that using modulo like this: unsigned long int result = ...
the_endian's user avatar
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4 votes
1 answer
712 views

Does rngd -r /path/to/file inject into /dev/urandom in addition to /dev/random?

I'm new to the /dev/random and /dev/urandom pipes in general and have an application calling from /dev/urandom which I'm attempting to inject entropy into. I'd prefer not to change the source for ...
CoryG's user avatar
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0 votes
2 answers
194 views

Will extra rules to my diceware list generation scheme decrease security?

I finished reading the Code Book by Simon Singh, I'm interested in playing with some of the ideas in the book to help increase my own understanding. I don't intend to implement the following in any ...
bbenz's user avatar
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0 votes
0 answers
24 views

How safe is a password generated from words? [duplicate]

I loathe passwords with completely random letters and digits. It's so much nicer to have a password made up of proper words. Even if the total length is much longer, it's easier to memorize, ...
TaylanKammer's user avatar
2 votes
1 answer
168 views

Does Docker affect the quality of cryptographic operations?

Is running cryptographic operations (encryption / decryption / signing / verifying / key-exchange / key-generation) in a Docker container affecting the quality of the crypto or entropy? If it does ...
user3200534's user avatar
9 votes
1 answer
4k views

Is reading from /dev/urandom on macOS Catalina a safe way to produce cryptographically secure data?

I'm reading a lot about entropy on macOS... I know it doesn't use Yarrow anymore as per this FIPS 140-02 doc a NIST compliant DRBG. I read a lot: https://github.com/briansmith/ring/pull/398 How ...
Woodstock's user avatar
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4 votes
1 answer
1k views

entropy change when reading from /dev/urandom vs /dev/random

I noticed that when reading from /dev/random, I have a very real impact on the entropy available on my linux box. (reading from /proc/system/kernel/random/entropy_avail), Yet when reading from /dev/...
Woodstock's user avatar
  • 689
3 votes
1 answer
424 views

using HW random number generator as source of entropy

Currently I am using haveged on my server as source of entropy. My Server is used as KVM hypervisor, to run virtual machines. I did not use haveged at the beginning, and I noticed the VMs were ...
Martin Vegter's user avatar
3 votes
2 answers
294 views

Quantify security strength from entropy and lifetime

Entropy or randomness is a quantitative measure of security strength for various types of passcodes, but in current times with digital technology, breaches, and cracking tools it seems that lifetime ...
gethopr's user avatar
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2 votes
0 answers
302 views

How much entropy does Apple Touch ID sensor read fingerprint has?

Iphone uses by default 6-digit PIN that has an entropy of 19.93 bits When iPhone processes the fingerprint, how much entropy does it have? How long should standard passphrase be until it is as ...
ccccc1cc's user avatar
1 vote
2 answers
333 views

If I seed a CSPRNG with a truly random number and call the output, does this make the number more, less or equally "random"?

If I have a JavaScript CSPRNG such as isaac.random(), and I seed it using a truly random number T as such: isaac.seed(T), does this make the result of the CSPRNG more, less, or equally random? I ...
Display Name's user avatar
4 votes
1 answer
505 views

What are some viable, secure sources of entropy for a CSPRNG?

I need some viable sources for entropy to seed a CSPRNG. So far, I have: JS Events Web Crypto API performance.now() Timing for xmlHTTPRequests etc. Are there any other viable/secure entropy sources ...
Display Name's user avatar
2 votes
1 answer
163 views

Is getting 1-2 outputs from a CSPRNG to seed another CSPRNG less entropy than getting say 5000 outputs from a CSPRNG and using that to seed?

This question builds off of this question. I want to create more entropy from a viable entropy source to seed another CSPRNG. If I use window.crypto.getRandomValues(newUint8Array(1)) To seed a ...
user avatar
1 vote
3 answers
264 views

Is using multiple instances of a browser-PRNG to seed another PRNG more secure?

Say I have Math.random() (which supposedly generates ~32 bits of entropy.) If I use Math.random() + Math.random(), both of them generate ~32 bits of entropy. I will use the solution of Math.random() +...
kNBDGYUIWKm's user avatar
14 votes
3 answers
13k views

How long should zip encryption password be for it take 10 years to crack?

I am using zip 3.0.0 on macOS High Sierra and Ubuntu. Here is my zip version on macOS: $ zip --version | head Copyright (c) 1990-2008 Info-ZIP - Type 'zip "-L"' for software license. This is ...
Lone Learner's user avatar
3 votes
2 answers
566 views

Generate cryptographically safe int

How can you generate a cryptographically safe integer that falls within a range in C#? I am trying to satisfy a Veracode issue reporting CWE-331: Insufficient Entropy. Obviously the code below is not ...
Hoppe's user avatar
  • 143
2 votes
1 answer
185 views

When knowing an individual's plaintext password history, how much information is expected to be gained with a new password? Do we know this?

The premise: Knowing a persons password history should provide information to help when guessing a new password of theirs. At an extreme end, with a password history of wildcats, wildcats1, then ...
lynn's user avatar
  • 715
0 votes
0 answers
259 views

Generating a secret token: security concerns other than min-entropy?

I'm trying to compare two techniques for generating an OAuth 2 PKCE code_verifier. For each character, get a random byte and "mod 66" to map to one of the 66 valid characters. For each ...
Kannan Goundan's user avatar
4 votes
3 answers
1k views

Determining the entropy of a string if each character has a slight bias

Let's say I need to generate a 32-character secret comprised of ASCII characters from the set '0'..'9'. Here's one way of doing it: VALID_CHARS = '0123456789' generate_secret_string() { random =...
Kannan Goundan's user avatar

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