/**
* Decrypt a RC2 encrypted string
*
* @param string $text A RC2 encrypted string
* @return boolean Returns true
*/
public function decrypt(&$text)
{
$this->operation(parent::DECRYPT);
// first split up the message into four 16 bit parts (2 bytes),
// then convert each array element to an integer
$w = self::splitBytes($text);
$k = self::splitBytes($this->xkey);
$j = 0;
// the key index
for ($i = 15; $i >= 0; --$i) {
$j = $i * 4;
/* This is where it gets ugly, RC2 relies on unsigned ints. PHP does
* not have a nice way to handle unsigned ints, so we have to rely on sprintf.
* To make RC2 compatible with mCrypt, I also forced everything to 32 bit
* When I test against mcrypt and the original rc2 C source, I get 32 bit
* results, even on a 64 bit platform
*/
$w[3] &= 65535;
$w[3] = parent::uInt($w[3] << 11) + parent::uInt($w[3] >> 5);
$w[3] -= parent::uInt($w[0] & ~$w[2]) + parent::uInt($w[1] & $w[2]) + $k[$j + 3];
$w[3] = parent::uInt32($w[3]);
$w[2] &= 65535;
$w[2] = parent::uInt($w[2] << 13) + parent::uInt($w[2] >> 3);
$w[2] -= parent::uInt($w[3] & ~$w[1]) + parent::uInt($w[0] & $w[1]) + $k[$j + 2];
$w[2] = parent::uInt32($w[2]);
$w[1] &= 65535;
$w[1] = parent::uInt($w[1] << 14) + parent::uInt($w[1] >> 2);
$w[1] -= parent::uInt($w[2] & ~$w[0]) + parent::uInt($w[3] & $w[0]) + $k[$j + 1];
$w[1] = parent::uInt32($w[1]);
$w[0] &= 65535;
$w[0] = parent::uInt($w[0] << 15) + parent::uInt($w[0] >> 1);
$w[0] -= parent::uInt($w[1] & ~$w[3]) + parent::uInt($w[2] & $w[3]) + $k[$j + 0];
$w[0] = parent::uInt32($w[0]);
if ($i == 5 || $i == 11) {
$w[3] -= $k[$w[2] & 63];
$w[2] -= $k[$w[1] & 63];
$w[1] -= $k[$w[0] & 63];
$w[0] -= $k[$w[3] & 63];
}
}
/* I am not clear why this is required. It was not mentioned
* in any of the documentation I read, however reading the original RC2 C
* source code, this was done and in order for me to get the
* correct results in PHP I needed to do this as well
*/
$max = count($w);
for ($i = 0; $i < $max; ++$i) {
$pos = $i * 2;
$text[$pos] = chr($w[$i]);
$text[$pos + 1] = chr($w[$i] >> 8);
}
return true;
}
/**
* The code for this function was translated to PHP from mcrypt's enigma.c,
* I was not able to find sufficient documentation to create my own
* version of this function.
* Enigma requires a 13 byte key, this function will
* lengthen the key to get it to 13 bytes long if it's short. It also
* Sets $deck, and $t1, $t2, $t3 which I think are the Enigma rotors.
*
* @return void
*/
private function createKey()
{
$this->deck = array();
$this->t1 = array();
$this->t2 = array_fill(0, self::ROTORSZ, 0);
$this->t3 = $this->t2;
$this->xkey = $this->key();
$klen = $this->keySize();
// get the key to exactly 13 bytes if it's less than 13
if ($klen < 13) {
$this->xkey = str_pad($this->xkey, 13, chr(0), STR_PAD_RIGHT);
}
$seed = 123;
for ($i = 0; $i < 13; ++$i) {
$seed = parent::sInt32($seed) * ord($this->xkey[$i]) + $i;
}
// sets $t1 and $deck
for ($i = 0; $i < self::ROTORSZ; ++$i) {
$this->t1[] = $i;
$this->deck[] = $i;
}
// sets $t3
for ($i = 0; $i < self::ROTORSZ; ++$i) {
// make sure the return values are 32 bit
$seed = 5 * parent::sInt32($seed) + ord($this->xkey[$i % 13]);
$seed = parent::sInt32($seed);
// force the returned value to be an unsigned int
//$random = parent::uint32($seed % 65521);
$random = parent::uInt($seed % 65521);
$k = self::ROTORSZ - 1 - $i;
$ic = ($random & self::MASK) % ($k + 1);
// make sure the returned value is an unsigned int
$random = parent::uInt($random >> 8);
$temp = $this->t1[$k];
$this->t1[$k] = $this->t1[$ic];
$this->t1[$ic] = $temp;
if ($this->t3[$k] != 0) {
continue;
}
$ic = ($random & self::MASK) % $k;
while ($this->t3[$ic] != 0) {
$ic = ($ic + 1) % $k;
}
$this->t3[$k] = $ic;
$this->t3[$ic] = $k;
}
// sets $t2
for ($i = 0; $i < self::ROTORSZ; ++$i) {
$pos = $this->t1[$i] & self::MASK;
$this->t2[$pos] = $i;
}
// now convert $t1, $t2, $t3, $deck values to signed chars,
// PHP's chr() function returns an unsigned char, so we have
// to use use our own
$this->t1 = array_map("parent::sChar", $this->t1);
$this->t2 = array_map("parent::sChar", $this->t2);
$this->t3 = array_map("parent::sChar", $this->t3);
$this->deck = array_map("parent::sChar", $this->deck);
}
