/**
* Initial Permutation (IP)
* Now we encode each 64-bit block of data. There is an initial permutation IP of
* the 64 bits of the message data M. This rearranges the bits according to the
* following table, where the entries in the table show the new arrangement of the
* bits from their initial order. The 58th bit of M becomes the first bit of IP.
* The 50th bit of M becomes the second bit of IP. The 7th bit of M is the last
* bit of IP.
*
* According to the book Applied Cryptography (Bruce Schneier, 2nd edition, pg. 271):
* The initial permution was used to make it easier to load plain text and cipher text
* data into a DES chip in byte-sized pieces when doing DES in hardware. The IP and FP
* are not necessary in software implementations and do not affect the security. However,
* the IP and FP are part of the DES standard and not implementing it would deviate from
* the standard, so we will do it here in phpCrypt.
*
* @param string $m The plain text message
* @return array the Initial Permutation (IP)
*/
private function ip($text)
{
$text = parent::str2Bin($text);
$ip = "";
// loop through the 64 bit block, ordering it occording to $_ip
for ($i = 0; $i < 64; ++$i) {
$ip .= $text[self::$_ip[$i] - 1];
}
return $ip;
}
