File Coverage

blib/lib/Math/Random/Secure/RNG.pm

Criterion	Covered	Total	%
statement	40	41	97.5
branch	11	14	78.5
condition	2	3	66.6
subroutine	12	12	100.0
pod	0	1	0.0
total	65	71	91.5

package Math::Random::Secure::RNG;
$Math::Random::Secure::RNG::VERSION = '0.08';
# ABSTRACT: The underlying PRNG, as an object.

use Moo;
use Math::Random::ISAAC;
use Crypt::Random::Source::Factory;
use constant ON_WINDOWS => $^O =~ /Win32/i ? 1 : 0;
use if ON_WINDOWS, 'Crypt::Random::Source::Strong::Win32';

has seeder => (
  is => 'ro',
  lazy => 1,
  builder => '_build_seeder',
);
# Default to a 512-bit key, which should be impossible to break. I wrote
# to the author of ISAAC and he said it's fine to not use a full 256
# integers to seed ISAAC.
has seed_size => (
  is => 'ro',
  # isa => 'Int',
  default => 64,
);

has seed => (
  is => 'rw',
  isa => \&_check_seed,
  lazy => 1,
  builder => '_build_seed',
  clearer => 'clear_seed',
  predicate => 'has_seed',
);

has rng => (
  is => 'ro',
  lazy => 1,
  builder => '_build_rng',
  handles => ['irand', 'rand'],
  clearer => 'clear_rng',
);

has _for_pid => (
  is => 'rw',
  default => sub { $$ },
);

sub _clear_for_pid { shift->_for_pid($$) }

before qw(irand rand) => '_maybe_clear_seed';

sub _maybe_clear_seed {
  my $self = shift;

  if ($self->_for_pid != $$) {
    $self->clear_seed;
    $self->_clear_for_pid;
  }
}


sub BUILD {
  my ($self) = @_;

  if ($self->seed_size < 8) {
    warn "Setting seed_size to less than 8 is not recommended";
  }
}

sub _check_seed {
  my ($seed) = @_;
  if (length($seed) < 8) {
    warn "Your seed is less than 8 bytes (64 bits). It could be"
      . " easy to crack";
  }
  # If it looks like we were seeded with a 32-bit integer, warn the
  # user that they are making a dangerous, easily-crackable mistake.
  # We do this during BUILD so that it happens during srand() in
  # Math::Secure::RNG.
  elsif (length($seed) <= 10 and $seed =~ /^\d+$/) {
    warn "RNG seeded with a 32-bit integer, this is easy to crack";
  }

  # _check_seed is used as a type constraint, so needs to return 1.
  return 1;
}

sub _build_seeder {
  my $factory = Crypt::Random::Source::Factory->new();
  # On Windows, we want to always pick Crypt::Random::Source::Strong::Win32,
  # which this will do.
  if (ON_WINDOWS) {
    return $factory->get_strong;
  }

  my $source = $factory->get;
  # Never allow rand() to be used as a source, it cannot possibly be
  # cryptographically strong with 2^15 or 2^32 bits for its seed.
  if ($source->isa('Crypt::Random::Source::Weak::rand')) {
    $source = $factory->get_strong;
  }
  return $source;
}

sub _build_seed {
  my ($self) = @_;
  return $self->seeder->get($self->seed_size);
}

sub _build_rng {
  my ($self) = @_;
  my @seed_ints = unpack('L*', $self->seed);
  my $rng = Math::Random::ISAAC->new(@seed_ints);
  # One part of having a cryptographically-secure RNG is not being
  # able to see the seed in the internal state of the RNG.
  $self->clear_seed;
  # It's faster to skip the frontend interface of Math::Random::ISAAC
  # and just use the backend directly. However, in case the internal
  # code of Math::Random::ISAAC changes at some point, we do make sure
  # that the {backend} element actually exists first.
  return $rng->{backend} ? $rng->{backend} : $rng;
}

1;

__END__