Hack the STH password

----------------hack.pl begin ------------------------
use strict;

die "Usage: $0 <stash file>\n" if $#ARGV != 0;

my $file=$ARGV[0];
open(F,$file) || die "Can't open $file: $!";

my $stash;
read F,$stash,1024;

my @unstash=map { $_^0xf5 } unpack("C*",$stash);

foreach my $c (@unstash) {
    last if $c eq 0;
    printf "%c",$c;
}
printf "\n";
---------------------hack.pl end-----------------

perl hack.pl key.sth
where key.sth is the stash file