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<?php |
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declare(strict_types = 1); |
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namespace Sop\PKCS5\PBEKD; |
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use Sop\PKCS5\PRF\PRF; |
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/** |
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* Implements key derivation function #2 used in password-based cryptography. |
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* |
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* @see https://tools.ietf.org/html/rfc2898#section-5.2 |
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*/ |
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class PBEKDF2 extends PBEKDF |
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{ |
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/** |
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* Pseudorandom functor. |
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* |
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* @var PRF |
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*/ |
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protected $_prf; |
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/** |
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* Constructor. |
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* |
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* @param PRF $prf |
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*/ |
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public function __construct(PRF $prf) |
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{ |
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$this->_prf = $prf; |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function derive(string $password, string $salt, int $count, |
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int $length): string |
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{ |
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$hlen = $this->_prf->length(); |
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$l = intval(ceil($length / $hlen)); |
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$r = $length - ($l - 1) * $hlen; |
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$blocks = []; |
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for ($i = 1; $i <= $l; ++$i) { |
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$blocks[] = $this->_f($password, $salt, $count, $i); |
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} |
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// truncate last block |
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$blocks[] = substr(array_pop($blocks), 0, $r); |
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$dk = implode('', $blocks); |
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return substr($dk, 0, $length); |
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} |
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/** |
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* XOR-sum function F. |
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* |
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* @param string $P |
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* @param string $S |
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* @param int $c |
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* @param int $i |
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* |
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* @return string |
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*/ |
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protected function _f(string $P, string $S, int $c, int $i): string |
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{ |
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// compute U_1 |
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$U = $this->_prf->compute($P, $S . pack('N', $i)); |
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$result = $U; |
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for ($x = 2; $x <= $c; ++$x) { |
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// U_x receives feedback from U_{x-1} |
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$U_x = $this->_prf->compute($P, $U); |
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// add to XOR-sum |
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$result ^= $U_x; |
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$U = $U_x; |
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} |
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return $result; |
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} |
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} |
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sop /
pkcs5
