Ask Lemmy

I see a lot of good answers here but let’s try it from another angle.

How do we get randomness from a function or formula?

For starters let’s setup a few simple rules.

Every time our random function is called we’ll

• Take the last output from a variable we call LAST_RESULT
• If there’s no value in LAST_RESULT we’ll assume the value is 1
• We run a set of calculations storing the value in a variable we call X
• We store the result of these calculations in LAST_RESULT
• We return this new “random” number.

So let’s call it.

> Random()
Since LAST_RESULT is undefined SET LAST_RESULT to the value of 1
Set X to the result of this calculation 
   (LAST_RESULT+1) * 3

X is now 6

Set X to the result of this calculation
   (X + 7) / 2

X is now 7

Set X to the result of this calculation (rounding to the nearest whole number)
   X/LAST_RESULT

X is now 7

Set LAST_RESULT to the value of X

LAST_RESULT is now 7

Return the value of X as the result 

Result is 7

Ok. So let’s call it again

 > Random()
Set X to the result of this calculation 
   (LAST_RESULT+1) * 3

X is now 24

Set X to the result of this calculation
   (X + 7) / 2

X is now 16

Set X to the result of this calculation (rounding to the nearest whole number)
   X/LAST_RESULT

X is now 2

Set LAST_RESULT to the value of X

LAST_RESULT is now 2

Return the value of X as the result

Result is 2

And if we call it again we get seemingly random results

Random() Result is 4

Random() Result is 3

But the next time you run it you’ll get the same results in the same order. 7, then 2 then 4 then 3

So what you need is something to “seed” the random number calculation.

Something like

SetRandomSeed Set LAST_RESULT to the current second of the day

Then when you call Random after this it starts with that as the prior results and gives seemingly random results.

Of course my calculations are rough and probably fail/repeat after so many calls but it gives you an idea of how this works.

So the trick is to get noise for the seed. That could be the number of non leap seconds since 00:00:00 UTC on Thursday, 1 January 1970 (Unix epoch)

Or the temperature reading of a CPU chip.

Maybe it’s the ratio of red vs yellow from a camera feed looking at lava lamps.

Or the current users average typing speed.

An additional note. Many of those would not be “cryptographically” secure for encryption because they can easily be determined by a third party. We all experience the same “Unix epoch” within a few milliseconds if our system clocks are properly set for example. Or monitored from afar and reproduced (hacked webcam shows they had just typed the following letters in the previous 27 seconds that we know the “algorithm” uses, etc.