/**
* Expand a 32 byte key, the size it is expanded to varies
* based on the block size of the Rijndael implementation chosen
*
* @return void
*/
private function expandKey256()
{
// clear the xkey, we're creating a new one
$this->xkey = "";
$max = 0;
// the number of rounds we make depends on the block size of the text
// used during encryption/decryption
if ($this->blockSize() == 16) {
$max = 60;
}
if ($this->blockSize() == 24) {
$max = 90;
}
if ($this->blockSize() == 32) {
$max = 120;
}
// 32 byte key expands to 240 bytes
for ($i = 0; $i < $max; ++$i) {
if ($i >= 0 && $i <= 7) {
$this->xkey .= $this->k($i * 4);
} else {
if ($i % 8 == 0) {
// rotate the 4 bytes
$subword = $this->rotWord($this->ek(($i - 1) * 4));
// apply the sbox
$this->subWord($subword);
// return 4 byte value based on self::$_rcon table
$rcon = $this->rcon($i / 8);
// grab 4 bytes from $this->extended_key
$ek = $this->ek(($i - 8) * 4);
$h1 = parent::str2Hex($subword);
$h2 = parent::dec2Hex($rcon);
$h3 = parent::str2Hex($ek);
$res = parent::xorHex($h1, $h2, $h3);
$this->xkey .= parent::hex2Str($res);
} else {
if ($i % 4 == 0) {
// get the subsitution from the s-box
$subword = $this->ek(($i - 1) * 4);
$this->subWord($subword);
// get the extended key part
$ek = $this->ek(($i - 8) * 4);
// xor the two parts
$h1 = parent::str2Hex($subword);
$h2 = parent::str2Hex($ek);
$res = parent::xorHex($h1, $h2);
$this->xkey .= parent::hex2Str($res);
} else {
$h1 = parent::str2Hex($this->ek(($i - 1) * 4));
$h2 = parent::str2Hex($this->ek(($i - 8) * 4));
$res = parent::xorHex($h1, $h2);
$this->xkey .= parent::hex2Str($res);
}
}
}
}
return true;
}
