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<?php
/**
* Copyright (c) 2014 Lukas Reschke <lukas@owncloud.com>
* This file is licensed under the Affero General Public License version 3 or
* later.
* See the COPYING-README file.
*/
namespace OC\Security;
use Crypt_AES;
use Crypt_Hash;
use OCP\Security\ICrypto;
use OCP\Security\ISecureRandom;
use OCP\Security\StringUtils;
use OCP\IConfig;
/**
* Class Crypto provides a high-level encryption layer using AES-CBC. If no key has been provided
* it will use the secret defined in config.php as key. Additionally the message will be HMAC'd.
*
* Usage:
* $encryptWithDefaultPassword = \OC::$server->getCrypto()->encrypt('EncryptedText');
* $encryptWithCustompassword = \OC::$server->getCrypto()->encrypt('EncryptedText', 'password');
*
* @package OC\Security
*/
class Crypto implements ICrypto {
/** @var Crypt_AES $cipher */
private $cipher;
/** @var int */
private $ivLength = 16;
/** @var IConfig */
private $config;
/** @var ISecureRandom */
private $random;
function __construct(IConfig $config, ISecureRandom $random) {
$this->cipher = new Crypt_AES();
$this->config = $config;
$this->random = $random;
}
/**
* @param string $message The message to authenticate
* @param string $password Password to use (defaults to `secret` in config.php)
* @return string Calculated HMAC
*/
public function calculateHMAC($message, $password = '') {
if($password === '') {
$password = $this->config->getSystemValue('secret');
}
// Append an "a" behind the password and hash it to prevent reusing the same password as for encryption
$password = hash('sha512', $password . 'a');
$hash = new Crypt_Hash('sha512');
$hash->setKey($password);
return $hash->hash($message);
}
/**
* Encrypts a value and adds an HMAC (Encrypt-Then-MAC)
* @param string $plaintext
* @param string $password Password to encrypt, if not specified the secret from config.php will be taken
* @return string Authenticated ciphertext
*/
public function encrypt($plaintext, $password = '') {
if($password === '') {
$password = $this->config->getSystemValue('secret');
}
$this->cipher->setPassword($password);
$iv = $this->random->getLowStrengthGenerator()->generate($this->ivLength);
$this->cipher->setIV($iv);
$ciphertext = bin2hex($this->cipher->encrypt($plaintext));
$hmac = bin2hex($this->calculateHMAC($ciphertext.$iv, $password));
return $ciphertext.'|'.$iv.'|'.$hmac;
}
/**
* Decrypts a value and verifies the HMAC (Encrypt-Then-Mac)
* @param string $authenticatedCiphertext
* @param string $password Password to encrypt, if not specified the secret from config.php will be taken
* @return string plaintext
* @throws \Exception If the HMAC does not match
*/
public function decrypt($authenticatedCiphertext, $password = '') {
if($password === '') {
$password = $this->config->getSystemValue('secret');
}
$this->cipher->setPassword($password);
$parts = explode('|', $authenticatedCiphertext);
if(sizeof($parts) !== 3) {
throw new \Exception('Authenticated ciphertext could not be decoded.');
}
$ciphertext = hex2bin($parts[0]);
$iv = $parts[1];
$hmac = hex2bin($parts[2]);
$this->cipher->setIV($iv);
if(!StringUtils::equals($this->calculateHMAC($parts[0].$parts[1], $password), $hmac)) {
throw new \Exception('HMAC does not match.');
}
return $this->cipher->decrypt($ciphertext);
}
}
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