File Coverage

blib/lib/Crypt/Skip32.pm

Criterion	Covered	Total	%
statement	66	66	100.0
branch	8	8	100.0
condition			n/a
subroutine	12	12	100.0
pod	5	5	100.0
total	91	91	100.0

package Crypt::Skip32;

use 5.008000;
use strict;
use warnings;
use Carp qw(croak);

if (not $ENV{CRYPT_SKIP32_PP} and eval 'use Crypt::Skip32::XS; 1') {
  *new = *Crypt::Skip32::XS::new;
}

our $VERSION = '0.19';

eval <<'EOP' if not defined &new;

# Number of bytes in the 4 byte (32-bit) block.
sub blocksize {
  return 4;
}

# Number of bytes in the 10 byte (80-bit) key.
sub keysize {
  return 10;
}

# New cipher constructor
sub new {
  my ($class, $key) = @_;

  my @key_bytes = unpack('C*', $key);
  croak "key must be 10 bytes long"
    unless scalar @key_bytes == 10;

  my $self = {
    key       => $key,
    key_bytes => \@key_bytes,
  };
  bless $self, $class;

  return $self;
}

# Encrypt a 4 byte (32-bit) block
sub encrypt {
  my ($self, $plaintext) = @_;

  my @input_bytes  = unpack('C*', $plaintext);
  croak "plaintext must be 4 bytes long"
    unless scalar @input_bytes == 4;
  my @output_bytes = _skip32($self->{key_bytes}, \@input_bytes, 1);
  my $cipher_text  = pack('C*', @output_bytes);

  return $cipher_text;
}

# Decrypt a 4 byte (32-bit) block
sub decrypt {
  my ($self, $ciphertext) = @_;

  my @input_bytes  = unpack('C*', $ciphertext);
  croak "ciphertext must be 4 bytes long"
    unless scalar @input_bytes == 4;
  my @output_bytes = _skip32($self->{key_bytes}, \@input_bytes, 0);
  my $plain_text   = pack('C*', @output_bytes);

  return $plain_text;
}

# Remaining Perl code is a direct translation of the SKIP32 C implementation

my @FTABLE =
(
0xa3,0xd7,0x09,0x83,0xf8,0x48,0xf6,0xf4,0xb3,0x21,0x15,0x78,0x99,0xb1,0xaf,0xf9,
0xe7,0x2d,0x4d,0x8a,0xce,0x4c,0xca,0x2e,0x52,0x95,0xd9,0x1e,0x4e,0x38,0x44,0x28,
0x0a,0xdf,0x02,0xa0,0x17,0xf1,0x60,0x68,0x12,0xb7,0x7a,0xc3,0xe9,0xfa,0x3d,0x53,
0x96,0x84,0x6b,0xba,0xf2,0x63,0x9a,0x19,0x7c,0xae,0xe5,0xf5,0xf7,0x16,0x6a,0xa2,
0x39,0xb6,0x7b,0x0f,0xc1,0x93,0x81,0x1b,0xee,0xb4,0x1a,0xea,0xd0,0x91,0x2f,0xb8,
0x55,0xb9,0xda,0x85,0x3f,0x41,0xbf,0xe0,0x5a,0x58,0x80,0x5f,0x66,0x0b,0xd8,0x90,
0x35,0xd5,0xc0,0xa7,0x33,0x06,0x65,0x69,0x45,0x00,0x94,0x56,0x6d,0x98,0x9b,0x76,
0x97,0xfc,0xb2,0xc2,0xb0,0xfe,0xdb,0x20,0xe1,0xeb,0xd6,0xe4,0xdd,0x47,0x4a,0x1d,
0x42,0xed,0x9e,0x6e,0x49,0x3c,0xcd,0x43,0x27,0xd2,0x07,0xd4,0xde,0xc7,0x67,0x18,
0x89,0xcb,0x30,0x1f,0x8d,0xc6,0x8f,0xaa,0xc8,0x74,0xdc,0xc9,0x5d,0x5c,0x31,0xa4,
0x70,0x88,0x61,0x2c,0x9f,0x0d,0x2b,0x87,0x50,0x82,0x54,0x64,0x26,0x7d,0x03,0x40,
0x34,0x4b,0x1c,0x73,0xd1,0xc4,0xfd,0x3b,0xcc,0xfb,0x7f,0xab,0xe6,0x3e,0x5b,0xa5,
0xad,0x04,0x23,0x9c,0x14,0x51,0x22,0xf0,0x29,0x79,0x71,0x7e,0xff,0x8c,0x0e,0xe2,
0x0c,0xef,0xbc,0x72,0x75,0x6f,0x37,0xa1,0xec,0xd3,0x8e,0x62,0x8b,0x86,0x10,0xe8,
0x08,0x77,0x11,0xbe,0x92,0x4f,0x24,0xc5,0x32,0x36,0x9d,0xcf,0xf3,0xa6,0xbb,0xac,
0x5e,0x6c,0xa9,0x13,0x57,0x25,0xb5,0xe3,0xbd,0xa8,0x3a,0x01,0x05,0x59,0x2a,0x46
);

sub _g {
  my ($rkey, $k, $w) = @_;
  my @key = @$rkey;

  my $g1 = ($w>>8)&0xff;
  my $g2 = $w&0xff;
  my $g3 = $FTABLE[$g2 ^ $key[(4*$k)%10]] ^ $g1;
  my $g4 = $FTABLE[$g3 ^ $key[(4*$k+1)%10]] ^ $g2;
  my $g5 = $FTABLE[$g4 ^ $key[(4*$k+2)%10]] ^ $g3;
  my $g6 = $FTABLE[$g5 ^ $key[(4*$k+3)%10]] ^ $g4;

  return (($g5<<8) + $g6);
}

sub _skip32 {
  my ($rkey, $rbuf, $encrypt) = @_;
  my @buf = @$rbuf;

  my $k; # round number
  my $i; # round counter
  my $kstep;
  my $wl;
  my $wr;

  # sort out direction
  if ($encrypt) {
    $kstep = 1;
    $k = 0;
  }
  else {
    $kstep = -1;
    $k = 23;
  }

  # pack into words
  $wl = ($buf[0] << 8) + $buf[1];
  $wr = ($buf[2] << 8) + $buf[3];

  # 24 feistel rounds, doubled up
  for ($i = 0; $i < 24/2; ++$i) {
    $wr ^= _g($rkey, $k, $wl) ^ $k;
    $k += $kstep;
    $wl ^= _g($rkey, $k, $wr) ^ $k;
    $k += $kstep;
  }

  # implicitly swap halves while unpacking
  $buf[0] = $wr >> 8;
  $buf[1] = $wr & 0xFF;
  $buf[2] = $wl >> 8;
  $buf[3] = $wl & 0xFF;

  return @buf;
}

EOP

1;

__END__