The generation of random or pseudorandom data, and the use of randomness in security protocols
31
votes
2answers
3k views
Is a rand from /dev/urandom secure for a login key?
Lets say I want to cookie for a user, would simply going to /dev/urandom, generating a 1024 bit string, checking if it already exists (and looping till I get a unique one) suffice? Or should I be ...
17
votes
8answers
4k views
Feeding /dev/random entropy pool?
Which way of additionally feeding /dev/random entropy pool would you suggest for producing random passwords? Or, is there maybe a better way to locally create fully random passwords?
8
votes
4answers
479 views
How insecure are non-cryptographic random number generators?
I always hear that C rand() is not secure, but what how many calls would you need to know in order to predict the next value (or at least cut down the possibilities)? Would they have to be sequential? ...
10
votes
5answers
1k views
Do mobile OS's provide crypto-quality randomness?
Which mobile OS's provide a primitive to generate crypto-quality randomness that applications can use?
On desktop systems, these features are pervasive. Unix provides /dev/urandom. Windows provides ...
6
votes
4answers
4k views
License key / Serial number generator and checker
I need a serial number generator and accompanying checker. I would like to be able to set a salt (and maybe a length). The generator should only produce serial numbers that pass the test of the ...
26
votes
5answers
2k views
Are GUIDs safe for one-time tokens?
I see a lot of sites use GUIDs for password resets, unsubscribe requests and other forms of unique identification.
Presumably they are appealing because they are easy to generate, unique, ...
13
votes
3answers
2k views
How long should a random nonce be?
NIST provides good guidelines on the length of keys and hashes for various algorithms. But I don't see anything specifically on the length of a random or pseudo-random nonce (number used once).
If ...
12
votes
3answers
219 views
What statistics can be used to identify pseudorandom data?
I'm working on some code that attempts to identify files whose contents appear to be "random". As such, I'm looking for statistical measures that can be used to identify such randomness.
I've ...
9
votes
2answers
2k views
Cracking a linear congruential generator
I was recently listening to the security now podcast, and they mentioned in passing that the linear congrunential generator (LCG) is trivial to crack. I use the LCG in a first year stats computing ...
3
votes
3answers
1k views
How insecure are PHP's rand functions?
There are some pseudo-random-number generators in PHP: rand(), srand(), mt_rand(), mt_srand(). You can look at their code here.
I understand those functions are insecure, but how insecure are they?
...
3
votes
1answer
294 views
Should I include a random padding in every HTTPS request and response?
According to the following paper, it is possible to decrypt HTTPS traffic by inspecting AJAX calls and using the size parameter as a cryptographic oracle.
Should I be sending a variable length ...
-5
votes
3answers
369 views
create a variants of MD5
I have also asked similar q here :
To create a variants of MD5, I made following changes :
MD5 uses a non-linear sin(i)* pow(2,32) ----> i plane to use cos(i)*pow(2,32)
Instead ...
11
votes
2answers
600 views
Evaluating the entropy gathering in a PRNG
I'm reviewing the random number generator (expected to be of cryptographic quality) on an embedded device. My point of view here is the operating system and crypto library implementer. I'm ...
11
votes
2answers
692 views
Flaw in encryption through pseudorandom number stream (from gpg documentation)
I was reading PGP docs and came upon a part written by Phil Zimmermann (PGP's creator) that piqued my curiosity:
When I was in college in the early 70s, I devised what I believed was a brilliant ...
6
votes
4answers
1k views
What do I need to configure, to make sure my software uses /dev/urandom?
When setting up a server, what configuration changes do I need to make sure that all of the software uses /dev/urandom instead of /dev/random?
Some servers don't have much entropy in the entropy pool ...
7
votes
4answers
642 views
Generate cryptographically strong pseudorandom numbers in Javascript?
Is there any good way to generate cryptographically strong pseudorandom (or true random) numbers in Javascript?
The crucial requirement: if a.com's Javascript generates some random numbers, no one ...
7
votes
5answers
541 views
Should passwords be truly random?
When generating a password, should it be "truly random" or should I make it a little less random by enforcing some rules?
If a password is generated at random, it could come out all-lowercase letters ...
7
votes
2answers
334 views
Is a rand from glibc's rand secure for a login key?
Same question as Is a rand from /dev/urandom secure for a login key, but with glibc's rand function instead of /dev/urandom. And what would be a sufficiently secure seed generator?
3
votes
3answers
355 views
Pseudo Random Generator is not initialized from the (entropy pool)?
The RHEL5 manuals state that /dev/urandom will use the entropy pool until it's exhausted, and then it will resort to a fall-back pseudo-random algorithm, so that it will never block.
But when ...
1
vote
1answer
198 views
What are the requirements for a random number generator to a be safe to use in cryptography?
When I look at most RNG's (random number generators), I see a disclaimer that looks similar to this:
Caution: Mersenne Twister is basically for Monte-Carlo simulations - it is not ...
