Questions tagged [random]
The generation of random or pseudorandom data, and the use of randomness in security protocols
0
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0answers
45 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
146 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
106 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
24 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
285 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
58 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
132 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
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0answers
40 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
295 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
122 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
395 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
304 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
64 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
74 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
54 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 ...
9
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 ...
1
vote
1answer
93 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
215 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, ...
3
votes
1answer
83 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
267 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
194 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
40 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
96 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
217 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
258 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
70 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
269 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
157 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
121 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
99 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
234 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
202 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 ...
1
vote
1answer
254 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?
22
votes
2answers
3k 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
159 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
223 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?
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vote
0answers
142 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
2k 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
711 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
...
10
votes
1answer
295 views
Random seed not propagating to the entropy pools in a timely manner
The Linux kernel's randomness driver collects entropy from the environment. Because there will be little entropy during boot, a random seed is often kept at /var/lib/misc/random-seed or a similar ...
3
votes
0answers
274 views
Entropy sources used by modern Windows
A comment on a Microsoft blog from 2005 mentions over 150 sources of entropy for the Windows CryptGenRandom function. The majority of sources come from low-level system information (precise stat ...
217
votes
11answers
43k views
Why is Math.random() not designed to be cryptographically secure?
The JavaScript Math.random() function is designed to return a single IEEE floating point value n such that 0 ≤ n < 1. It is (or at least should be) widely known that the output is not ...
3
votes
1answer
142 views
Linux 'add_interrupt_randomness' implementation - low entropy contribution by cycles and jiffies?
Currently I'm analyzing the process of entropy generation of a Linux 64-bit kernel during system startup (for educational purpose). The system is hosted as/on a (64 bit) virtual machine (Xen domU). ...
3
votes
1answer
6k views
Need advices on API key & secret generation?
While working on a Java project using Spring-boot, Spring-security and JWT token, I need to provide access via API key and secret. After searching on Google for a while about key/secret generation, ...
0
votes
1answer
77 views
Key Generation on FIPS device or using SW with FIPS generator
I would like to understand the difference between these two options how to generate AES key.
AES key is generated directly in FIPS 140-2 Level 3 device with validated AES
algorithm
AES key is ...
2
votes
3answers
137 views
XOR of many prime sized cycles: secure?
I thought of a PRNG which is dependent on a large amount of good salt. The method is to use the salt to fill many arrays whose lengths are prime numbers, and cycle through each array, and ouput the ...
1
vote
1answer
134 views
Generating a secret on a compromised computer
Suppose we are on a compromised computer (for example infested with trojans logging key presses or taking screenshots) and for some reason we have to generate a number that's supposed to be secret for ...
4
votes
2answers
272 views
What role do hashing and block ciphers play in random number generation?
I read about pseudo random number generators and there were certain demands on which "underlying hash function" and "underlying block cipher" to use. What role do hashing algorithms and block ciphers ...
5
votes
1answer
174 views
How would someone attack a not truly random secret produced by a human?
Especially in cryptocurrencies you often hear people say that private key/seeds should not be typed "randomly" by humans, but rather use a truly random number generator. I understand, that humans ...
