. sorry to be a wet blanket, but it doesn’t help on my system (Strawberry Perl, Windows 8.1, 64-bit):

Of course not. It would need to have been used by the author when constructing the obfu.

However, there are a few situations where programs are likely to
want to call "srand". One is for generating predictable results,
generally for testing or debugging. There, you use
"srand($seed)", with the same $seed each time.
[download]

I do think that the breakage of srand($seed) between 5.20 and earlier perls should have been spelled out in the srand documentation ... probably worth a bug report from someone who cares.

As documented in the 5.20 delta:

rand now uses a consistent random number generator Previously perl would use a platform specific random number generator, varying between the libc rand(), random() or drand48(). This meant that the quality of perl's random numbers would vary from platform to platform, from the 15 bits of rand() on Windows to 48-bits on POSIX platforms such as Linux with drand48(). Perl now uses its own internal drand48() implementation on all platforms. This does not make perl's rand cryptographically secure.

The effect of srand was platform specific. Ie different between Windows & *nix. And that is the cause of the failures for the obfu.

From 5.20 on, that problem goes away because of the built-in rand/srand rather inheriting them from the platform C compiler implementation.

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Ie different between Windows & *nix. And that is the cause of the failures for the obfu

Yes, I think that's the cause of most of the failures - but not the one that Athanasius experienced with Strawberry Perl. My Strawberry Perl 5.20.0 produces the same as Athanasius got:

C:\_32\strawberry5.20.0>perl -e "srand 42; print sort {4-rand 9} split
+ //, 'ts aroMrhirsae C tll!!ym';"
l ttyaMeos  arrCsrihm!!l
[download]

But when I switch to 5.18.2 it all works as intended:

C:\_32\strawberry5.18.2>perl -e "srand 42; print sort {4-rand 9} split
+ //, 'ts aroMrhirsae C tll!!ym';"
Merry Christmas to all!!
C:\_32\strawberry5.18.2>
[download]

And it also works as expected for me all the way back to 5.8.8 (which is as far back as I go).

From 5.20 on, that problem goes away because of the built-in rand/srand rather inheriting them from the platform C compiler implementation.

Agreed, and it was worth doing for that very reason.
I just think they should have mentioned, in the srand documentation, that srand(42) would produce different results (on Windows) for 5.20.0 as compared to earlier perl versions - but the srand documentation (as it stands) suggests to me that no such change is to be expected.

Cheers,
Rob