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<?php |
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/* |
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* The MIT License (MIT) |
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* |
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* Copyright (c) 2014-2016 Spomky-Labs |
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* |
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* This software may be modified and distributed under the terms |
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* of the MIT license. See the LICENSE file for details. |
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*/ |
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namespace AESKW; |
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use Assert\Assertion; |
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trait AESKW |
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{ |
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/** |
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* The initial value used to wrap the key and check the integrity when unwrapped. |
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* The RFC3394 set this value to 0xA6A6A6A6A6A6A6A6 |
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* The RFC5649 set this value to 0xA65959A6XXXXXXXX (The part with XXXXXXXX is the MLI, depends on the padding). |
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* |
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* @param string $key The key |
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* @param bool $padding_enabled Enable padding (RFC5649) |
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* |
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* @return string |
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* |
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* @see https://tools.ietf.org/html/rfc3394#section-2.2.3.1 |
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*/ |
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private static function getInitialValue(&$key, $padding_enabled) |
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{ |
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if (false === $padding_enabled) { |
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return hex2bin('A6A6A6A6A6A6A6A6'); |
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} |
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$MLI = mb_strlen($key, '8bit'); |
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$iv = hex2bin('A65959A6').self::toXBits(32, $MLI); |
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$n = intval(ceil($MLI / 8)); |
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$key = str_pad($key, 8 * $n, "\0", STR_PAD_RIGHT); |
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return $iv; |
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} |
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/** |
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* @param string $key |
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* @param bool $padding_enabled |
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* @param string $iv |
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* |
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* @return bool |
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*/ |
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private static function checkInitialValue(&$key, $padding_enabled, $iv) |
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{ |
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// RFC3394 compliant |
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if ($iv === hex2bin('A6A6A6A6A6A6A6A6')) { |
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return true; |
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} |
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// The RFC3394 is required but the previous check is not satisfied => invalid |
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if (false === $padding_enabled) { |
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return false; |
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} |
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// The high-order half of the AIV according to the RFC5649 |
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if (hex2bin('A65959A6') !== self::getMSB($iv)) { |
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return false; |
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} |
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$n = mb_strlen($key, '8bit') / 8; |
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$MLI = hexdec(bin2hex(ltrim(self::getLSB($iv), "\0"))); |
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if (!(8 * ($n - 1) < $MLI && $MLI <= 8 * $n)) { |
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return false; |
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} |
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$b = 8 * $n - $MLI; |
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for ($i = 0; $i < $b; ++$i) { |
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if ("\0" !== mb_substr($key, $MLI + $i, 1, '8bit')) { |
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return false; |
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} |
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} |
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$key = mb_substr($key, 0, $MLI, '8bit'); |
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return true; |
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} |
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/** |
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* @param string $key The Key to wrap |
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* @param bool $padding_enabled |
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*/ |
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private static function checkKeySize($key, $padding_enabled) |
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{ |
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Assertion::false(false === $padding_enabled && 0 !== mb_strlen($key, '8bit') % 8, 'Bad key size'); |
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Assertion::greaterOrEqualThan(mb_strlen($key, '8bit'), 1, 'Bad key size'); |
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} |
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/** |
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* @param string $kek The Key Encryption Key |
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* @param string $key The key to wrap |
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* @param bool $padding_enabled If false, the key to wrap must be a sequence of one or more 64-bit blocks (RFC3394 compliant), else the key size must be at least one octet (RFC5649 compliant) |
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* |
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* @return string The wrapped key |
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*/ |
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public static function wrap($kek, $key, $padding_enabled = false) |
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{ |
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self::checkKEKSize($kek); |
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$A = self::getInitialValue($key, $padding_enabled); |
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self::checkKeySize($key, $padding_enabled); |
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$P = str_split($key, 8); |
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$N = count($P); |
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$C = []; |
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$encryptor = self::getEncryptor($kek); |
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if (1 === $N) { |
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$B = $encryptor->encrypt($A.$P[0]); |
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$C[0] = self::getMSB($B); |
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$C[1] = self::getLSB($B); |
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} elseif (1 < $N) { |
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$R = $P; |
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for ($j = 0; $j <= 5; ++$j) { |
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for ($i = 1; $i <= $N; ++$i) { |
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$B = $encryptor->encrypt($A.$R[$i - 1]); |
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$t = $i + $j * $N; |
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$A = self::toXBits(64, $t) ^ self::getMSB($B); |
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$R[$i - 1] = self::getLSB($B); |
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} |
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} |
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$C = array_merge([$A], $R); |
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} |
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return implode('', $C); |
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} |
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/** |
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* @param string $kek The Key Encryption Key |
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* @param string $key The key to unwrap |
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* @param bool $padding_enabled If false, the AIV check must be RFC3394 compliant, else it must be RFC5649 or RFC3394 compliant |
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* |
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* @return string The key unwrapped |
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*/ |
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public static function unwrap($kek, $key, $padding_enabled = false) |
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{ |
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self::checkKEKSize($kek); |
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$P = str_split($key, 8); |
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$A = $P[0]; |
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$N = count($P); |
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Assertion::greaterThan($N, 1, 'Bad data'); |
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$encryptor = self::getEncryptor($kek); |
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if (2 === $N) { |
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$B = $encryptor->decrypt($P[0].$P[1]); |
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$unwrapped = self::getLSB($B); |
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$A = self::getMSB($B); |
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} else { |
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$R = $P; |
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for ($j = 5; $j >= 0; --$j) { |
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for ($i = $N - 1; $i >= 1; --$i) { |
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$t = $i + $j * ($N - 1); |
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$B = $encryptor->decrypt((self::toXBits(64, $t) ^ $A).$R[$i]); |
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$A = self::getMSB($B); |
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$R[$i] = self::getLSB($B); |
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} |
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} |
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unset($R[0]); |
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$unwrapped = implode('', $R); |
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} |
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Assertion::true(self::checkInitialValue($unwrapped, $padding_enabled, $A), 'Integrity check failed'); |
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return $unwrapped; |
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} |
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/** |
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* @param int $bits |
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* @param int $value |
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* |
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* @return string |
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*/ |
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private static function toXBits($bits, $value) |
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{ |
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return hex2bin(str_pad(dechex($value), $bits / 4, '0', STR_PAD_LEFT)); |
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} |
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/** |
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* @param string $value |
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* |
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* @return string |
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*/ |
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private static function getMSB($value) |
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{ |
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return mb_substr($value, 0, mb_strlen($value, '8bit') / 2, '8bit'); |
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} |
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/** |
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* @param string $value |
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* |
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* @return string |
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*/ |
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private static function getLSB($value) |
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{ |
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return mb_substr($value, mb_strlen($value, '8bit') / 2, null, '8bit'); |
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} |
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/** |
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* @param string $kek |
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* |
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* @return \AESKW\EncryptorInterface |
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*/ |
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private static function getEncryptor($kek) |
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{ |
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if (extension_loaded('openssl')) { |
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return new OpenSSLEncryptor($kek); |
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} |
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throw new \RuntimeException('Please install OpenSSL extension.'); |
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} |
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} |
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