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<?php
declare(strict_types=1);
/**
* @copyright Copyright (c) 2016, ownCloud, Inc.
*
* @author Andreas Fischer <bantu@owncloud.com>
* @author Christoph Wurst <christoph@winzerhof-wurst.at>
* @author Lukas Reschke <lukas@statuscode.ch>
* @author lynn-stephenson <lynn.stephenson@protonmail.com>
* @author Morris Jobke <hey@morrisjobke.de>
* @author Roeland Jago Douma <roeland@famdouma.nl>
*
* @license AGPL-3.0
*
* This code is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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, version 3,
* along with this program. If not, see <http://www.gnu.org/licenses/>
*
*/
namespace OC\Security;
use OCP\IConfig;
use OCP\Security\ICrypto;
use OCP\Security\ISecureRandom;
use phpseclib\Crypt\AES;
use phpseclib\Crypt\Hash;
/**
* 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 AES $cipher */
private $cipher;
/** @var int */
private $ivLength = 16;
/** @var IConfig */
private $config;
/**
* @param IConfig $config
* @param ISecureRandom $random
*/
public function __construct(IConfig $config) {
$this->cipher = new AES();
$this->config = $config;
}
/**
* @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(string $message, string $password = ''): string {
if ($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 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(string $plaintext, string $password = ''): string {
if ($password === '') {
$password = $this->config->getSystemValue('secret');
}
$keyMaterial = hash_hkdf('sha512', $password);
$this->cipher->setPassword(substr($keyMaterial, 0, 32));
$iv = \random_bytes($this->ivLength);
$this->cipher->setIV($iv);
$ciphertext = bin2hex($this->cipher->encrypt($plaintext));
$iv = bin2hex($iv);
$hmac = bin2hex($this->calculateHMAC($ciphertext.$iv, substr($keyMaterial, 32)));
return $ciphertext.'|'.$iv.'|'.$hmac.'|3';
}
/**
* 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
* @throws \Exception If the decryption failed
*/
public function decrypt(string $authenticatedCiphertext, string $password = ''): string {
if ($password === '') {
$password = $this->config->getSystemValue('secret');
}
$hmacKey = $encryptionKey = $password;
$parts = explode('|', $authenticatedCiphertext);
$partCount = \count($parts);
if ($partCount < 3 || $partCount > 4) {
throw new \Exception('Authenticated ciphertext could not be decoded.');
}
$ciphertext = $this->hex2bin($parts[0]);
$iv = $parts[1];
$hmac = $this->hex2bin($parts[2]);
if ($partCount === 4) {
$version = $parts[3];
if ($version >= '2') {
$iv = $this->hex2bin($iv);
}
if ($version === '3') {
$keyMaterial = hash_hkdf('sha512', $password);
$encryptionKey = substr($keyMaterial, 0, 32);
$hmacKey = substr($keyMaterial, 32);
}
}
$this->cipher->setPassword($encryptionKey);
$this->cipher->setIV($iv);
if (!hash_equals($this->calculateHMAC($parts[0] . $parts[1], $hmacKey), $hmac)) {
throw new \Exception('HMAC does not match.');
}
$result = $this->cipher->decrypt($ciphertext);
if ($result === false) {
throw new \Exception('Decryption failed');
}
return $result;
}
private function hex2bin(string $hex): string {
if (!ctype_xdigit($hex)) {
throw new \RuntimeException('String contains non hex chars: ' . $hex);
}
if (strlen($hex) % 2 !== 0) {
throw new \RuntimeException('Hex string is not of even length: ' . $hex);
}
$result = hex2bin($hex);
if ($result === false) {
throw new \RuntimeException('Hex to bin conversion failed: ' . $hex);
}
return $result;
}
}
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