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Re: $RANDOM not Cryptographically secure pseudorandom number generator

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  Re: $RANDOM not Cryptographically secure pseudorandom number generator Ole Tange <tange@gnu.org> - 2019-01-02 02:29 +0100
    Re: $RANDOM not Cryptographically secure pseudorandom number generator Luuk <luuk@invalid.lan> - 2019-01-02 12:01 +0100

#15027 — Re: $RANDOM not Cryptographically secure pseudorandom number generator

On Mon, Dec 31, 2018 at 8:12 PM Chet Ramey <chet.ramey@case.edu> wrote:
:
> Thanks for the patch. I'll take a look after I release bash-5.0. One
> question: can you reproduce the same random sequence by using the same
> seed? That's for backwards compatibility, even if the sequences themselves
> differ.

Yes. Seeding with a value will give the same sequence:

$ RANDOM=4; echo $RANDOM $RANDOM
21584 22135

$ RANDOM=4; echo $RANDOM $RANDOM
21584 22135

For backwards compatibility integers are supported, but they are
really parsed as strings. Strings make it easier to seed with more
than 64-bits:

RANDOM=`cat GPLv3.txt`

So these give the same value on 4.4.23, but differs with the patch applied:

RANDOM=$(echo 2^64 | bc );echo $RANDOM
RANDOM=$(echo 2^65 | bc );echo $RANDOM

RANDOM="foo"; echo $RANDOM
RANDOM="bar"; echo $RANDOM

RANDOM=2; echo $RANDOM
RANDOM=" 2.0"; echo $RANDOM
RANDOM=" 2.0noise"; echo $RANDOM


/Ole

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#15032

On 2-1-2019 02:29, Ole Tange wrote:
> On Mon, Dec 31, 2018 at 8:12 PM Chet Ramey <chet.ramey@case.edu> wrote:
> :
>> Thanks for the patch. I'll take a look after I release bash-5.0. One
>> question: can you reproduce the same random sequence by using the same
>> seed? That's for backwards compatibility, even if the sequences themselves
>> differ.
> 
> Yes. Seeding with a value will give the same sequence:
> 
> $ RANDOM=4; echo $RANDOM $RANDOM
> 21584 22135
> 
> $ RANDOM=4; echo $RANDOM $RANDOM
> 21584 22135
> 

But not across systems:
luuk@WINDOWS:/mnt/c/Windows/System32$ RANDOM=4;echo $RANDOM $RANDOM
1692 27588
luuk@WINDOWS:/mnt/c/Windows/System32$ RANDOM=4;echo $RANDOM $RANDOM
1692 27588

luuk@opensuse:~> RANDOM=4; echo $RANDOM $RANDOM
32221 21043
luuk@opensuse:~> RANDOM=4; echo $RANDOM $RANDOM
32221 21043

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