Questions tagged [random]
The generation of random or pseudorandom data, and the use of randomness in security protocols
332
questions
2
votes
1answer
76 views
Is this schema between a Desktop App and an API secure?
From my previous question: How secure is this schema between a Desktop App (c++) and an API (php).
Introduction
I made a paid Desktop-app that required constant internet connection (because of its ...
2
votes
3answers
77 views
Benefits of signing a random number?
Is there any benefit to signing a random number?
E.g. a link for password reset, sent to email, often includes a base64 encoded random number to prevent someone guessing what the password reset link ...
0
votes
0answers
28 views
What is the difference between /dev/random and /dev/urandom? [duplicate]
Simply put, what are the differences between /dev/random and /dev/urandom from a developer's standpoint? Which one should I use for cryptographic purposes?
1
vote
2answers
83 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 ...
1
vote
1answer
71 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 ...
2
votes
1answer
76 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 ...
1
vote
3answers
94 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() +...
0
votes
1answer
86 views
Find seed used in Math.random LCG given a list of outputs [duplicate]
Given one or two sequential Math.random outputs generated with Internet Explorer's linear congruential generator, is it possible to find the seed used in the LCG and find subsequent outputs? Here is ...
0
votes
1answer
106 views
Predicting Math.random() sequence using V8's MWC1616 algorithm
If you have the seeds for Math.random() using mwc1616, are the random numbers generated in the same order every time / are they repeating? Basically wondering if, given a seed, can I predict past ...
0
votes
0answers
60 views
How long will it take to crack a hashed random string
If I generate 128 bit, 512 bit and 1024 bit random strings using either:
A native rand() function (C, PHP, Python, etc)
OpenSSL random bytes
Hardware generated random number
And hash the random ...
0
votes
0answers
49 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 character, get ...
3
votes
3answers
173 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 =...
0
votes
1answer
110 views
Am I making my One-Time Passcode less secure?
I am using some "magic link" one-time passcodes for automatically logging users in for a specific purpose on our website.
My plan is to generate a hash based on the datetime, users specific "ID" and ...
0
votes
0answers
45 views
When should I use CryptoPP::AutoSeededRandomPool (not CryptoPP::NonblockingRng)?
I found CryptoPP provides several random generators: CryptoPP::AutoSeededRandomPool, CryptoPP::AutoSeededX917RNG and so on. I know some details about these generators and the usage of them, I just ...
1
vote
3answers
301 views
Exactly how is a pseudorandom number generator a security risk?
I was recently reading about Diceware, which is essentially a list of words from which several can be picked to form a long passphrase. The website stresses that these words should be picked randomly ...
0
votes
1answer
68 views
What does “probabilistic algorithm with random tape” mean?
I am new to the study of cryptography, and when reading papers they often mention that "probabilistic algorithm G with random tape w ...". What does it mean by "random tape w"? I mean why it does is ...
2
votes
1answer
227 views
Is it safe to use a passphrase to seed fernet key generation?
I have a cluster deployment that depends on a Fernet Key to secure some data. The deployment script generates the key with:
FERNET_KEY=$(python -c "from cryptography.fernet import Fernet; k = Fernet....
1
vote
0answers
43 views
Can Lava Lamps enhance modern native entropy sourced from hardware and the Linux Kernel? [duplicate]
In this 2017 video by Computerphile's Tom Scott, "The Lava Lamps That Help Keep The Internet Secure", Scott tours Cloud Flare's facility and checks out their Wall of Entropy. This is essentially a ...
2
votes
1answer
641 views
How can I increase /proc/sys/kernel/random/entropy_avail
I have access to genuine random numbers - random.org, for example.
I have a number of processes using /dev/random and my value for /proc/sys/kernel/random/entropy_avail is 143, which is pretty low.
...
4
votes
1answer
132 views
Is pressing random keys a secure way to seed a key generator?
There's a couple of programs that I've been using recently that ask you to type random keys as a source of randomness to seed an RNG for key generation.
Is this considered a good practice still, or ...
16
votes
2answers
458 views
What research suggests that user's mouse movements are (not) sufficiently unpredictable for secret key generation?
I have not been able to find any credible source which tried to prove or disprove the randomness of mouse movements.
A Google Scholar search for "mouse movement entropy" gives surprisingly few ...
7
votes
3answers
385 views
Is PuttyGen secure?
I'm using PuttyGen to generate ssh keys for various windows computers. It requires a lot of manual user input, specifically in the form of swirling the mouse around in the window pane. I understand ...
0
votes
2answers
66 views
How to solve the problem of secure randomly generated GUIDs when the size of the data outgrows the GUIDs
I've been struggling with this problem for a little while... How to hide the order that records were created in, basically. You typically do this by generating a "GUID". But this GUID is arbitrarily ...
1
vote
1answer
76 views
Size of a secure random number taking into account quantum computing and size of universe
Most random secure numbers are 256 to 512 bits. But given the size of the universe and eventually quantum computing, I am wondering what is a better sized randomly generated number, taking into ...
1
vote
0answers
82 views
Does using both a counter and a random nonce make sense for the purpose of reducing the likelihood of replay attacks?
I am aware that using a counter or a random value are both acceptable ways of generating nonces, depending on the circumstances.
The tradeoff with using a counter is the necessity to keep state and ...
10
votes
2answers
1k views
Is there a loss of entropy by hashing an N-bit random key to produce an N-bit hash?
I read the following piece of code:
dd if=/dev/urandom bs=16 count=1 2>/dev/null | md5sum
Apparently, this code was used as a trick to produce a hex string key from a 128-bit binary pseudo-random ...
0
votes
1answer
104 views
What is the entropy of a call to java.lang.Math.random()?
Math.random() produces a double value (IEEE 754 binary64) in the range [0.0, 1.0). How many digits (or bits) of entropy does the return value of random() contain?
If it simplifies things, I'm okay ...
1
vote
3answers
437 views
What should a secure passphrase look like?
We all know that passwords should not only be randomly generated, but also look random. The reason is that attackers can use patterns or existing words to be able to bruteforce the passwords faster, ...
4
votes
1answer
113 views
How do GnuPG smartcard generate reliable random data?
I'm generating a private key on my new GPG smartcard at this very moment.
On linux, the random would be fed by the keystrokes on my keyboard, the network packets, the mouse movements etc.
How does ...
6
votes
4answers
352 views
Are there any practical attacks on random number generators?
I'm creating an internal security course for developers. To make it more interesting, I'm trying to reinforce each chapter with some real-world attacks but stumbled upon insecure random usage section.
...
2
votes
3answers
217 views
Password-hash proofing SHA-3
I am in a situation where I need to harden a password hash, but not allowed to bring in any extra dependencies, so I am pretty much forced to do the one thing everyone seems to advise against - roll ...
0
votes
1answer
42 views
Is it necessary to verify that my order confirmation IDs are unique?
I'm generating 9-character order confirmations such as K1YBFRG17, O1D15ZCOM, etc and using them as order confirmation numbers. It's basically just picking at random from the string '...
1
vote
1answer
115 views
The NIST randomness tests for a generated key
Does different tests for key randomness provided by NIST are available online? where one can test that which test for key generated are passed and which are failed?
2
votes
1answer
328 views
Is RDRAND used in a safe way by Windows 10?
This question was already answered by Linus Torvalds for Linux, and is also cited in this Q/A on this stack:
We use rdrand as _one_ of many inputs into the random pool, and we use it as a way to ...
2
votes
2answers
342 views
When you XOR a random number with non-random number, does that give you a new random number?
XOR has the following truth table:
0, 0 : 0
0, 1 : 1
1, 0 : 1
1, 1 : 0
So per bit in an XOR operation, there is a 50% chance of that result being 1 and 50% chance of it being 0. If you XOR a random ...
2
votes
2answers
92 views
Should you use SecureRandom.getInstance() with or without a provider?
So, I am new to cryptography and I was learning about SecureRandom and all of the ways it calls implementations with or without providers.
When I looked up some sites for information, it says not to ...
0
votes
2answers
491 views
/dev/random generate session key
if a server uses /dev/random to generate the random session key with a client. How you can launch a Denial-Of-Service (DOS) attack on such a server?
1
vote
1answer
226 views
Mobile application authentication using UUID
I write back-end code for mobile applications. I am needing to write the code for authentication and the simplest yet secure solution I can think of is:
When user signs in, device sends username and ...
2
votes
1answer
123 views
For a “normal” computer user, does it make a difference to have a good entropy source?
Let's take, for example, Linux. From my understanding, there are different sources and different ways that can be used to gather entropy (RNG daemon, Intel rrandr, TPM, etc). Some produce entropy that ...
72
votes
5answers
14k views
What makes Random Number Generators so fragile?
It seems to me that a hardware component which generates random numbers is extremely simple - just measure tiny vibrations in the hardware with a sensor, right? Maybe I'm wrong but it seems like if ...
1
vote
1answer
133 views
What function is used to generate client random in TLS
I've been learning TLS. During the Client-Server Hello their random values are shared. The client generates a 28 byte random and combine it with 4 bytes of epoch time to generate a 32 byte random ...
1
vote
1answer
294 views
How to reverse engineer str_shuffle (PHP) to get its mt_rand outputs
$output = str_shuffle("12345");
E.g. $output is now 25134
How do I find out what numbers came out of mt_rand() to allow for the shuffle
I want to know this because I want the seed of mt_rand() and ...
0
votes
1answer
251 views
Is a substring of base64 encoded random_bytes less secure then just using random_bytes
$bytes = random_bytes(15);
$encoded = base64_encode($bytes);
$output = substr($encoded, 0, 15);
Does this code affect the complexity of the output vs just using
$output = random_bytes(15);
I think ...
2
votes
1answer
293 views
Would `cat /dev/random` be a denial of service to any other users of `/dev/random`?
As in the question. Wouldn't cat /dev/random decrease the entropy estimate until it blocks, which forces the random device to block for all applications on the current system?
24
votes
2answers
4k views
Is “always use /dev/urandom” still good advice in an age of containers and isolation?
In short: Instead of another question asking about when to use /dev/random instead of /dev/urandom, I present the following scenario, in which I find myself in an application I'm building:
A VM or ...
1
vote
1answer
180 views
Does OpenSSH use padding of random lengths?
According to the end of RFC 4253 § 6, the random padding introduced to each SSH packet is an arbitrary multiple of 8. It mentions that random padding lengths can mitigate traffic analysis:
Note ...
2
votes
1answer
237 views
Injecting data into the Windows entropy pool
On Linux, it is possible for userspace to mix arbitrary data with the kernel entropy pool by writing to the /dev/urandom device. Is there any equivalent on Windows which does not require SYSTEM?
1
vote
0answers
160 views
Problem in Cracking PHP rand() seed on windows
I read this article https://www.sjoerdlangkemper.nl/2016/02/11/cracking-php-rand/ about cracking php rand() function. and I involved with some problems on testing methods mentioned in article. I used ...
-3
votes
1answer
4k views
How to correctly use dev/urandom for random generation [closed]
Runs before main:
d -c 30 /dev/urandom > random.bytes
Access the randomly generated numbers
int main() {
FILE *fp;
int fd = open("random.bytes",O_RDONLY);
fp = fopen("file.txt" , ...
8
votes
1answer
951 views
Unix command to generate cryptographically secure random string
Is the following Unix command cryptographically secure to randomly generate 20 characters (a-zA-Z0-9 only)?
dd if=/dev/urandom bs=256 count=1 2> /dev/null | LC_ALL=C tr -dc 'A-Za-z0-9' | head -c20
...
