[Cryptography Team] Re: Random is not random at startup

[Robert Withers]

Thanks for cc-ing me. I don't have much exposure to random, so I am 
cc-ing the Cryptography list, in hopes they might help. This doesn't 
very random, you're right. Here were Peter's questions:

    My questions:
    1) do we really want to have global fixed seed?
    2) Random new should actually setup a usable seed so I don't need to
    first run it N times before I can use the value
    3) Should we switch to what UUIDGenerator is using… reading
    /dev/urandom for the initial seed setup?

Rob


On 05/18/2016 07:05 PM, Peter Uhnák wrote:
> Hi,
>
> (cc-ing Robert Withers as he seems to be working with cryptography and 
> security... as this seems related and may have some implications, but 
> I am likely wrong about the implications)
>
> yesterday I've encountered a very surprising behavior
>
> I executed the same script `10 atRandom` on the same image without 
> saving it and got the same output:
>
> while true; do
>         pharo-vm --nodisplay latest.image --no-default-preferences 
> eval '10 atRandom'
> done
> 10
> 10
> 10
> 10
> 10
> 10
>
> Not so random… not random at all.
>
> Apparently the default random generator uses SharedRandom pool, that 
> is initialized only once… so every time you start an image you get the 
> EXACT same random seed... I think this is stupid, and I am not sure 
> what are the security implications of this (e.g. when opening an SSL 
> connection… having fixed world-wide initial seed seems like an awful, 
> awful idea), but whatever…
>
> So instead I tried to explicitly specify the Random generator… which I 
> can do
>
> while true; do
>         pharo-vm --nodisplay latest.image --no-default-preferences 
> eval '10 atRandom: Random new'
> done
> 5
> 5
> 5
> 5
> 5
>
> Still not random… what?
>
> while true; do
>         pharo-vm --nodisplay latest.image --no-default-preferences 
> eval 'Random new instVarNamed: #seed'
> done
> 426306047
> 426305545
> 426305546
> 426306010
>
> So the seed is different but thanks to the magic of masking the seed, 
> I always get the same first several bits… thus the same result for 
> small numbers.
>
> So if I actually want what seems like a random value… I have to at 
> least once run the generator…
>
> while true; do
>         pharo-vm --nodisplay latest.image --no-default-preferences 
> eval '10 atRandom: (Random new next; yourself)'
> done
> 7
> 3
> 4
> 9
> 6
> 7
>
> Once I start to use it the properties of the algo kick in so it's 
> pseudo-random… but I need to run it once to initialize it, which is wtf.
>
> My questions:
> 1) do we really want to have global fixed seed?
> 2) Random new should actually setup a usable seed so I don't need to 
> first run it N times before I can use the value
> 3) Should we switch to what UUIDGenerator is using… reading 
> /dev/urandom for the initial seed setup?
>
> Peter

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