Re: A strange function behaviour in random password generator

[nix@xxxxxxxxxxxxxxxx]

> On Mon, 6 Dec 2010 14:39:41 +0100
> Mikael Magnusson <mikachu@xxxxxxxxx> wrote:
>> On 6 December 2010 14:15,  <nix@xxxxxxxxxxxxxxxx> wrote:
>> > Hi, I have just coded a random password generator. It works good
>> > but one might want to show me how to do it with rand48() as its
>> > output is strange.
>> >
>> > The problem:
>> >
>> > ./random_pass.sh
>> > iNkiuG
>> > iNkiuG6K
>> >
>> > 6 first chars are the same for both passwords.
>>
>> > [...]
>>
>> > pos=$((RANDOM%$seeds_count+1))
>> > MY_RCON=$(random 6)
>> > MY_PASS=$(random 8)
>>
>> If you access $RANDOM in a subshell, the parent shell doesn't know
>> about it, and next time it forks a subshell the state will be
>> identical.
>

Thanks Mikael for pointing it out.

> That's what the seed argument for rand48 is for.  Here's a function that
> creates a seed in a file and always uses that file.  The new random number
> is in $REPLY.  There are all sorts of possible improvements.
>
> rand48() {
>   local sfile=~/.zsh_rand48
>   zmodload -i zsh/mathfunc
>
>   if [[ ! -f $sfile ]]; then
>     touch $sfile
>     chmod 600 $sfile
>     # Warning: this is not very random.
>     # OK for pseudorandom statistics, bad for security.
>     printf "%.4x%.4x%.4x\n" $RANDOM $RANDOM $RANDOM >$sfile
>   fi
>
>   local seed="$(<$sfile)"
>
>   typeset -g REPLY=$(( rand48(seed) ))
>
>   print $seed >$sfile
> }
>
>

I think I could now write the same password generator using rand48() based
on your example but i am afraid I would have to use external commands for
sorting the output.

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> Peter Stephenson <pws@xxxxxxx>            Software Engineer
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