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<?php
/**
* @copyright Copyright (c) 2018 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\Monitor;
use OCA\RansomwareDetection\Classifier;
class SequenceAnalyzer
{
/**
* Number of information files.
*
* @var int
*/
const NUMBER_OF_INFO_FILES = 10;
/** @var SequenceSizeAnalyzer */
private $sequenceSizeAnalyzer;
/** @var FileTypeFunnellingAnalyzer */
private $fileTypeFunnellingAnalyzer;
/** @var EntropyFunnellingAnalyzer */
private $entropyFunnellingAnalyzer;
/**
* SequenceAnalyzer constructor.
*
* @param SequenceSizeAnalyzer $sequenceSizeAnalyzer
* @param FileTypeFunnellingAnalyzer $fileTypeFunnellingAnalyzer
* @param EntropyFunnellingAnalyzer $entropyFunnellingAnalyzer
*/
public function __construct(
SequenceSizeAnalyzer $sequenceSizeAnalyzer,
FileTypeFunnellingAnalyzer $fileTypeFunnellingAnalyzer,
EntropyFunnellingAnalyzer $entropyFunnellingAnalyzer
) {
$this->sequenceSizeAnalyzer = $sequenceSizeAnalyzer;
$this->fileTypeFunnellingAnalyzer = $fileTypeFunnellingAnalyzer;
$this->entropyFunnellingAnalyzer = $entropyFunnellingAnalyzer;
}
/**
* The analysis of the sequence is seperated in three parts:
* The analysis: If the same number of files is deletedFilesd as written,
* with the special addition that the number of written files is in the
* range of [number of deletedFilesd files, number of deletedFilesd files + 4].
* To enhance this analysis the sum of the size of the files deletedFilesd and
* the sum of the size of the written files is compared.
*
* The next part is the analysis of the suspicion levels of the files written.
* Therefor the suspicions levels are weighted:
* Suspicious - 1
* Maybe suspicious - 0.5
* Not suspicious - 0.25
*
* summed up and divided by the sum of all written files. The higher the result,
* the higher is the suspicion of the hole sequence.
*
* The last part is the file type funneling analysis.
*
* @param int $sequenceId
* @param array $sequence
*
* @return SequenceResult
*/
public function analyze($sequenceId, $sequence)
{
$sequenceResult = new SequenceResult($sequenceId, 0, 0, 0, 0, $sequence);
if (sizeof($sequence) === 0) {
return $sequenceResult;
}
$files = ['written' => [], 'sizeWritten' => 0, 'deleted' => [], 'sizeDeleted' => 0, 'suspicious' => [], 'maybeSuspicious' => [], 'notSuspicious' => []];
$suspicionScore = 0;
foreach ($sequence as $file) {
if ($file->getType() === 'file') {
switch ($file->getCommand()) {
case Monitor::WRITE:
$files['written'][] = $file;
$files['sizeWritten'] = $files['sizeWritten'] + $file->getSize();
break;
case Monitor::READ:
break;
case Monitor::RENAME:
break;
case Monitor::DELETE:
$files['deleted'][] = $file;
$files['sizeDeleted'] = $files['sizeDeleted'] + $file->getSize();
break;
case Monitor::CREATE:
break;
default:
break;
}
switch ($file->getSuspicionClass()) {
case Classifier::SUSPICIOUS:
$files['suspicious'][] = $file;
break;
case Classifier::MAYBE_SUSPICIOUS:
$files['maybeSuspicious'][] = $file;
break;
case Classifier::NOT_SUSPICIOUS:
$files['notSuspicious'][] = $file;
break;
case Classifier::NO_INFORMATION:
break;
default:
break;
}
}
}
// compare files written and files deleted
if (sizeof($files['written']) > 0 && sizeof($files['deleted']) > 0) {
$sequenceResult->setSizeWritten($files['sizeWritten']);
$sequenceResult->setSizeDeleted($files['sizeDeleted']);
$upperBound = sizeof($files['deleted']) + self::NUMBER_OF_INFO_FILES;
if (sizeof($files['written']) <= $upperBound && sizeof($files['written']) >= sizeof($files['deleted'])) {
if ($this->sequenceSizeAnalyzer->analyze($sequence) === SequenceSizeAnalyzer::EQUAL_SIZE) {
$sequenceResult->setQuantities(2);
$suspicionScore += 2;
} else {
$sequenceResult->setQuantities(1);
$suspicionScore += 1;
}
}
}
$numberOfWrittenFiles = sizeof($files['suspicious']) + sizeof($files['maybeSuspicious']) + sizeof($files['notSuspicious']);
// remove info files from the weight
$numberOfInfoFiles = self::NUMBER_OF_INFO_FILES;
if (sizeof($files['notSuspicious']) < self::NUMBER_OF_INFO_FILES) {
$numberOfInfoFiles = sizeof($files['notSuspicious']);
}
// weight the suspicion levels.
$suspicionSum = (sizeof($files['suspicious']) * 1) + (sizeof($files['maybeSuspicious']) * 0.5) + ((sizeof($files['notSuspicious']) - $numberOfInfoFiles) * 0.25);
// check for division by zero.
if (($numberOfWrittenFiles - $numberOfInfoFiles) > 0) {
$sequenceResult->setFileSuspicion($suspicionSum / ($numberOfWrittenFiles - $numberOfInfoFiles));
$suspicionScore += $suspicionSum / ($numberOfWrittenFiles - $numberOfInfoFiles);
}
// entropy funnelling
$entropyFunnelling = $this->entropyFunnellingAnalyzer->analyze($files['deleted'], $files['written']);
$sequenceResult->setEntropyFunnelling($entropyFunnelling);
$suspicionScore += $entropyFunnelling->getEntropyFunnelling();
// check for file type funneling
$fileTypeFunnelling = $this->fileTypeFunnellingAnalyzer->analyze($sequence);
$sequenceResult->setFileTypeFunnelling($fileTypeFunnelling);
$suspicionScore += $fileTypeFunnelling;
$sequenceResult->setSuspicionScore($suspicionScore);
return $sequenceResult;
}
}
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