package Config;

$key = 'hello';

package Foo;

use Devel::Peek;

my $str = 'the key is:';
Dump($Config::key);
decrypt( $str, $Config::key );

$Config::key = 'x'x19;
Dump($Config::key);
decrypt( $str, $Config::key );

$Config::key = 'x'x20;
Dump($Config::key);
decrypt( $str, $Config::key );

sub decrypt{ warn "Got: @_\n" }

__DATA__
SV = PV(0x15d5284) at 0x1a454a0
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0x15dd0ac "hello"\0
  CUR = 5
  LEN = 6
Got: the key is: hello
SV = PV(0x15d5284) at 0x1a454a0
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0x15dd0ac "xxxxxxxxxxxxxxxxxxx"\0 <--- Same Pointer == overwrite
  CUR = 19
  LEN = 20
Got: the key is: xxxxxxxxxxxxxxxxxxx
SV = PV(0x15d5284) at 0x1a454a0
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0x1a48edc "xxxxxxxxxxxxxxxxxxxx"\0 <--- Reallocation has occurred
  CUR = 20
  LEN = 21
Got: the key is: xxxxxxxxxxxxxxxxxxxx