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<?php
/**
* @copyright Copyright (c) 2017 Matthias Held <matthias.held@uni-konstanz.de>
* @author Matthias Held <matthias.held@uni-konstanz.de>
* @license GNU AGPL version 3 or any later version
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
namespace OCA\RansomwareDetection\Analyzer;
use OCA\RansomwareDetection\FileSignatureList;
use OCA\RansomwareDetection\Entropy\Entropy;
use OCP\ILogger;
class FileNameAnalyzer
{
/**
* File name entropy cut-off point between normal and suspicious.
*
* @var float
*/
const ENTROPY_CUT_OFF = 4.0;
/** @var ILogger */
private $logger;
/** @var Entropy */
private $entropy;
/**
* @param ILogger $logger
* @param Entropy $entropy
*/
public function __construct(
ILogger $logger,
Entropy $entropy
) {
$this->logger = $logger;
$this->entropy = $entropy;
}
/**
* Classifies a file name in NORMAL, SUSPICIOUS_FILE_NAME,
* SUSPICIOUS_FILE_EXTENSION or SUSPICIOUS, if the file name
* and file extension are suspicious.
*
* @param string $path
*
* @return FileNameResult
*/
public function analyze($path)
{
$fileName = $this->getFileName($path);
$extension = $this->getFileExtension($path);
$class = FileNameResult::NORMAL;
$isFileExtensionKnown = $this->isFileExtensionKnown($extension);
if (!$isFileExtensionKnown) {
$class += FileNameResult::SUSPICIOUS_FILE_EXTENSION;
}
$entropyOfFileName = $this->calculateEntropyOfFileName($fileName);
if ($entropyOfFileName > self::ENTROPY_CUT_OFF) {
$class += FileNameResult::SUSPICIOUS_FILE_NAME;
}
return new FileNameResult($class, $isFileExtensionKnown, $entropyOfFileName);
}
/**
* Checks if the file extension is known.
*
* @param string $extension
*
* @return bool
*/
private function isFileExtensionKnown($extension)
{
$signatures = FileSignatureList::getSignatures();
foreach ($signatures as $signature) {
if (in_array(strtolower($extension), $signature['extension'])) {
return true;
}
}
return false;
}
/**
* Returns the file name of a path.
*
* @param string $path
*
* @return string
*/
private function getFileName($path)
{
$file = pathinfo($path);
return $file['basename'];
}
/**
* Returns the file extension of a file name.
*
* @param string $fileName
*
* @return string
*/
private function getFileExtension($fileName)
{
$file = pathinfo($fileName);
return $file['extension'];
}
/**
* Calculates the entropy of the a file name.
*
* @param string $fileName
*
* @return float
*/
private function calculateEntropyOfFileName($fileName)
{
return $this->entropy->calculateEntropy($fileName);
}
}
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