115
votes
Why do some people believe that humans are "bad at" generating random numbers/characters like this?
In short, it is more than a belief: there is strong evidence that humans are not good entropy sources. There is a test for this
Man vs. Machine. Or, why Man is not a Particularly Good Source of ...
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66
votes
Accepted
Are one-time pads crackable in theory?
For example, for a target bitstring of 100 bits, I cannot scan all bitstrings of 100 bits and XOR each with the target, hoping to recover the message. This approach will produce all messages that can ...
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46
votes
Accepted
What is the practical impact of using System.Random which is not cryptographically random?
You asked for the practical impact, so the answer is that for \$120 I could probably have your entire password database done by tomorrow.
Here is your program, or something similar to it:
...
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40
votes
Accepted
What does it mean for a random number generator to be cryptographically secure?
What are the criteria that make an RNG cryptographically secure?
In short, a DRBG [deterministic random bit generator] is formally considered computationally secure if a computationally-limited ...
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38
votes
Cryptography's random number problem?
The title of this article is complete hype. Tip: when a journalist says “X could solve Y”, read “X probably won't solve Y”. Much of the content of the article is hype too.
Cryptography has a random ...
35
votes
Accepted
How can C rand() be exploited if a secure seed is used?
The ISO/IEC 9899:1990 edition of the C standard contains:
EXAMPLE The following functions define a portable implementation of rand and ...
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34
votes
Why is the output of a True Random Number Generator (TRNG) insecure after it has been compressed?
I think you're misinterpreting the source. The source says the TRNGs "rely" on compression (a cryptographic hash would be the compression function, or possibly some simpler function to ...
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32
votes
Accepted
A website that identifies an RNG from its output
A colleague of mine told me about a website that, given a sufficient quantity of output from an PRNG, had been able to deduce which application the PRNG was from.
As you correctly identified this ...
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31
votes
Why do some people believe that humans are "bad at" generating random numbers/characters like this?
For me, the fraud-related applications of Benford's Law come to mind. When people make up data they tend to create overly uniform data, even when it's not appropriate. There's a definite psychology ...
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29
votes
A website that identifies an RNG from its output
One tool that tries to do this is untwister. It's almost certainly not the tool you were thinking of, though, as it cannot determine if the output came from OpenSSL specifically.
It can determine ...
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26
votes
Accepted
What is the difference between TRNG and CSPRNG?
A True Random Number Generator uses a physical phenomenon not known to be fully deterministic as origin of the discrete values (bits or integer numbers) that it outputs. That phenomenon can for ...
- 138k
26
votes
What is the practical impact of using System.Random which is not cryptographically random?
From what you have described, it sounds like your system works as follows:
Consult the system clock to find a 32-bit seed $s$.
Use System.Random to generate a ...
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24
votes
Are one-time pads crackable in theory?
To begin with, your definition of perfect secrecy is non-standard. The standard definition is given in an excellent answer to the question how is the OTP perfectly secure?.
Essentially, perfect ...
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23
votes
Accepted
How many hex digits do I need to compare when manually checking hash functions?
How many hex digits do I need to compare when manually checking hash
functions?
If you actually want the full security guarantees of the hash function to apply: all of them.
I usually just look ...
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21
votes
Using Tweets as a Random seed
The other answers provide very good lists of reasons not to use Twitter as an entropy source. What follows is the flip side of your question:-
Why would you want to?
Tweets are typically read on ...
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20
votes
Accepted
Using Tweets as a Random seed
What you are suggesting is not a good idea for a general purpose random number generator. It could be meaningful for very specific use cases if you need a random number generator whose output can be ...
- 1,377
18
votes
What is the practical impact of using System.Random which is not cryptographically random?
The official documentation for System.Random explicitly says it should not be used for generating passwords. It’s predictable, and seeded only from the system clock. This means System.Random has at ...
- 2,287
18
votes
Why do some people believe that humans are "bad at" generating random numbers/characters like this?
Why would a dice rolled be "more random" than simply coming up with a
sequence in your head, and then changing some of them?
Humans have too many biases regarding what a random sequence is. ...
17
votes
What does it mean for a random number generator to be cryptographically secure?
I tried to use mostly non-jargon to make it more understandable than the current top answer.
What are the criteria that make an RNG cryptographically secure?
From en.wikipedia.org/wiki/CSPRNG:
...
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17
votes
Accepted
XOR a set of random numbers
Assuming that $b = 2^k-1$ for some positive integer $k$, XORing two (or more) numbers in the range $[0,b]$ will indeed yield a number in the same range.
If the numbers are random, uniformly ...
- 45.9k
16
votes
Example of cryptography random number
What kind of numbers are needed for cryptography/security? Are those integers?
Bits. Simply have your TRNG generate random bits.
As mentioned in the other answer, the only difference between bits/...
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15
votes
Accepted
Why do we require a CSPRNG's output to be indistinguishable from true random?
We simply strive for crypto that's as close as possible to ideal. Indistinguishably is the strongest property we can demand from a PRNG/streamcipher.
It's hard to predict which non ideal properties ...
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15
votes
Using Tweets as a Random seed
How are you going to decide which tweet to use? Randomly? This quickly leads to a chicken / egg problem.
What if the chosen tweet is one word? That would not add a lot of entropy.
What if twitter is ...
- 91.7k
15
votes
Why do some people believe that humans are "bad at" generating random numbers/characters like this?
Randomness is a measurable, statistical property of a set of values. It doesn't mean the same as "hard for a human to guess."
Your sample string is hard for a human to guess, but it isn't ...
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14
votes
How can C rand() be exploited if a secure seed is used?
I once played this online game, it was an old-school MUD. You log in, chat, kill some goblins.
It had a casino. You go into the casino and you bet X gold, and there was a 40% chance you win double ...
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14
votes
How many hex digits do I need to compare when manually checking hash functions?
If you control both ends as well as the transfer channel - for example if you are transferring a large file between two of your own computers via a USB drive - then it's OK to only verify the hash ...
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14
votes
Radioactive Decay, Gaussian or Uniform?
You can just follow the instructions on HotBits, which is exactly what you're trying to build. It's been running for years and is the only radioactive TRNG on the internet. It goes into great depth ...
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14
votes
Why do some people believe that humans are "bad at" generating random numbers/characters like this?
People are not that bad, but we're slow. See How were one-time pads and keys historically generated? In summary, MB's of 100% secure key material were generated for one time pads by people simply key ...
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13
votes
Are one-time pads crackable in theory?
I'll try a practical example:
I trade stocks. Instructions to my broker use a simple Caesar shift cipher, but the shift varies by values in a one-time encryption pad. Common 8-char instructions ...
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13
votes
Examples of frauds discovered because someone tried to mimic a random sequence
Following my comment, and even though it's a bit different from what you ask: I really enjoyed the story here where the use of an incorrect pseudorandom number generator led to the arrest of members ...
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Only top scored, non community-wiki answers of a minimum length are eligible