3 ms·

Situations where there is no cryptographic issue in sight and random number generation is a bottleneck. Graphics and simulations in games, for example

Thorrez 6y ago
Does that actually require unpredictability? Or is it just a defense in depth type thing where we believe we don't need it, but some unknown vulnerability/attack might make unpredictability beneficial?
- sgillen 6y ago
  The numbers used here are not for security they are just to make the scene look nice or to make the simulation more robust.
  - Thorrez 6y ago
    So I think we agree that unpredictability isn't necessary. The definition of unpredictability I'm using is the one on the website: where Mersenne Twister is easily predictable.
- Karliss 6y ago
  Looking at your and other comments there might be confusion about definition of unpredictability. Unpredictable for user which is pretty low bar or unpredictable using best known mathematical techniques and available hardware. Wouldn't the second category be more less CSPRNG? As for first category and examples given. Requires is a weird question. Strongly requires as in it's impossible to make any game or visual effect without it - no. But in case of some design choices you might want some amount of unpredictability. You might want player not to fully predict enemies next move, or you might want a certain graphical effect which varies some parameter randomly within some distribution. Using a very poor pseudorandom generator there might became visible once it gets used in large amounts for placing objects spatially in the form of streaks, shapes or other patterns that wouldn't appear if true random or better quality psrng was used.
  - Thorrez 6y ago
    I think I and andreareina are using the definition from the website. Yes, I think other people are using other definitions, which is causing confusion. > Wouldn't the second category be more less CSPRNG? The website says PCG is "Challenging" to predict and ChaCha20 is "Secure". So I think this means that PCG isn't a CSPRNG, but still is harder to predict than Mersenne Twister. But is this useful at all? I don't know. This thread started by andreareina asking that exact question: "What applications require unpredictability where you wouldn't go full csprng?" People immediately then misunderstood the question because they misunderstood how the word unpredictability is being used. A player not being able to mentally predict enemies and not seeing visible patterns sounds like it might fall more under the website's definition of "Statistical Quality".
- Kednicma 6y ago
  Yes: http://extremelearning.com.au/unreasonable-effectiveness-of-quasirandom-sequences/ http://extremelearning.com.au/unreasonable-effectiveness-of-... Sibling comments are completely correct. Graphics simulations often require quasirandom sequences; the particular sequence is not important, but any correlations in the sequence will be visible in the output as artifacts, so we want a decorrelated sequence. If this is not enough of a real-world example for you, then Monte Carlo methods also show up in weather modeling, financial planning, and election forecasting. In those predictive systems, there is extreme uncertainty and dependence on initial conditions, which we model with quasirandom sequences and seed numbers respectively. By running many simulations with different random sequences and then examining all of the results statistically, we can get good estimates of future behavior. Edit: Oh, you're not in good faith. Okay, cool story. Best of luck with whatever imaginary idea of "unpredictability" you're trying to define, but you might want to return to actual maths at some point.
  - Thorrez 6y ago
    Quasirandom is unrelated to anything we're talking about. Quasirandom intentionally makes the output very different from random (avoiding clustering). Every other thing in the PCG website and in this thread attempts to be similar to random (with varying degrees of success). No one here is trying to intentionally be different from random. > Sibling comments are completely correct. No sibling comment says anything about quasirandom. The sibiling comment mentioning graphics (by Karliss) actually sort of disagrees with you, and says that we want stuff to be as close to random as possible for graphics so that players don't see patterns. Of course there can be multiple types of graphics situations, some where quasirandom would be useful (the blog you linked), some where a real random approximation would be useful (Karliss's situation).
- vanderZwan 6y ago
  Ah, I see what you mean! I was unknowingly being sloppy with terms, thank you for pointing that out.

Thorrez 6y ago

Does that actually require unpredictability? Or is it just a defense in depth type thing where we believe we don't need it, but some unknown vulnerability/attack might make unpredictability beneficial?

sgillen 6y ago
The numbers used here are not for security they are just to make the scene look nice or to make the simulation more robust.
- Thorrez 6y ago
  So I think we agree that unpredictability isn't necessary. The definition of unpredictability I'm using is the one on the website: where Mersenne Twister is easily predictable.
Karliss 6y ago
Looking at your and other comments there might be confusion about definition of unpredictability. Unpredictable for user which is pretty low bar or unpredictable using best known mathematical techniques and available hardware. Wouldn't the second category be more less CSPRNG? As for first category and examples given. Requires is a weird question. Strongly requires as in it's impossible to make any game or visual effect without it - no. But in case of some design choices you might want some amount of unpredictability. You might want player not to fully predict enemies next move, or you might want a certain graphical effect which varies some parameter randomly within some distribution. Using a very poor pseudorandom generator there might became visible once it gets used in large amounts for placing objects spatially in the form of streaks, shapes or other patterns that wouldn't appear if true random or better quality psrng was used.
- Thorrez 6y ago
  I think I and andreareina are using the definition from the website. Yes, I think other people are using other definitions, which is causing confusion. > Wouldn't the second category be more less CSPRNG? The website says PCG is "Challenging" to predict and ChaCha20 is "Secure". So I think this means that PCG isn't a CSPRNG, but still is harder to predict than Mersenne Twister. But is this useful at all? I don't know. This thread started by andreareina asking that exact question: "What applications require unpredictability where you wouldn't go full csprng?" People immediately then misunderstood the question because they misunderstood how the word unpredictability is being used. A player not being able to mentally predict enemies and not seeing visible patterns sounds like it might fall more under the website's definition of "Statistical Quality".
Kednicma 6y ago
Yes: http://extremelearning.com.au/unreasonable-effectiveness-of-quasirandom-sequences/ http://extremelearning.com.au/unreasonable-effectiveness-of-... Sibling comments are completely correct. Graphics simulations often require quasirandom sequences; the particular sequence is not important, but any correlations in the sequence will be visible in the output as artifacts, so we want a decorrelated sequence. If this is not enough of a real-world example for you, then Monte Carlo methods also show up in weather modeling, financial planning, and election forecasting. In those predictive systems, there is extreme uncertainty and dependence on initial conditions, which we model with quasirandom sequences and seed numbers respectively. By running many simulations with different random sequences and then examining all of the results statistically, we can get good estimates of future behavior. Edit: Oh, you're not in good faith. Okay, cool story. Best of luck with whatever imaginary idea of "unpredictability" you're trying to define, but you might want to return to actual maths at some point.
- Thorrez 6y ago
  Quasirandom is unrelated to anything we're talking about. Quasirandom intentionally makes the output very different from random (avoiding clustering). Every other thing in the PCG website and in this thread attempts to be similar to random (with varying degrees of success). No one here is trying to intentionally be different from random. > Sibling comments are completely correct. No sibling comment says anything about quasirandom. The sibiling comment mentioning graphics (by Karliss) actually sort of disagrees with you, and says that we want stuff to be as close to random as possible for graphics so that players don't see patterns. Of course there can be multiple types of graphics situations, some where quasirandom would be useful (the blog you linked), some where a real random approximation would be useful (Karliss's situation).
vanderZwan 6y ago
Ah, I see what you mean! I was unknowingly being sloppy with terms, thank you for pointing that out.