nextcloud/apps/encryption/lib/Crypto/Crypt.php

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<?php
/**
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* @copyright Copyright (c) 2016, ownCloud, Inc.
*
* @author Bjoern Schiessle <bjoern@schiessle.org>
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* @author Björn Schießle <bjoern@schiessle.org>
* @author Christoph Wurst <christoph@winzerhof-wurst.at>
* @author Clark Tomlinson <fallen013@gmail.com>
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* @author Joas Schilling <coding@schilljs.com>
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* @author Lukas Reschke <lukas@statuscode.ch>
* @author Morris Jobke <hey@morrisjobke.de>
* @author Roeland Jago Douma <roeland@famdouma.nl>
* @author Stefan Weiberg <sweiberg@suse.com>
* @author Thomas Müller <thomas.mueller@tmit.eu>
*
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* @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/>
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*
*/
namespace OCA\Encryption\Crypto;
use OC\Encryption\Exceptions\DecryptionFailedException;
use OC\Encryption\Exceptions\EncryptionFailedException;
use OC\ServerNotAvailableException;
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use OCA\Encryption\Exceptions\MultiKeyDecryptException;
use OCA\Encryption\Exceptions\MultiKeyEncryptException;
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use OCP\Encryption\Exceptions\GenericEncryptionException;
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use OCP\IConfig;
use OCP\IL10N;
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use OCP\ILogger;
use OCP\IUserSession;
/**
* Class Crypt provides the encryption implementation of the default Nextcloud
* encryption module. As default AES-256-CTR is used, it does however offer support
* for the following modes:
*
* - AES-256-CTR
* - AES-128-CTR
* - AES-256-CFB
* - AES-128-CFB
*
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* For integrity protection Encrypt-Then-MAC using HMAC-SHA256 is used.
*
* @package OCA\Encryption\Crypto
*/
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class Crypt {
public const DEFAULT_CIPHER = 'AES-256-CTR';
// default cipher from old Nextcloud versions
public const LEGACY_CIPHER = 'AES-128-CFB';
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// default key format, old Nextcloud version encrypted the private key directly
// with the user password
public const LEGACY_KEY_FORMAT = 'password';
public const HEADER_START = 'HBEGIN';
public const HEADER_END = 'HEND';
/** @var ILogger */
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private $logger;
/** @var string */
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private $user;
/** @var IConfig */
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private $config;
/** @var array */
private $supportedKeyFormats;
/** @var IL10N */
private $l;
/** @var array */
private $supportedCiphersAndKeySize = [
'AES-256-CTR' => 32,
'AES-128-CTR' => 16,
'AES-256-CFB' => 32,
'AES-128-CFB' => 16,
];
/** @var bool */
private $supportLegacy;
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/**
* @param ILogger $logger
* @param IUserSession $userSession
* @param IConfig $config
* @param IL10N $l
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*/
public function __construct(ILogger $logger, IUserSession $userSession, IConfig $config, IL10N $l) {
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$this->logger = $logger;
$this->user = $userSession && $userSession->isLoggedIn() ? $userSession->getUser()->getUID() : '"no user given"';
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$this->config = $config;
$this->l = $l;
$this->supportedKeyFormats = ['hash', 'password'];
$this->supportLegacy = $this->config->getSystemValueBool('encryption.legacy_format_support', false);
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}
/**
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* create new private/public key-pair for user
*
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* @return array|bool
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*/
public function createKeyPair() {
$log = $this->logger;
$res = $this->getOpenSSLPKey();
if (!$res) {
$log->error("Encryption Library couldn't generate users key-pair for {$this->user}",
['app' => 'encryption']);
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if (openssl_error_string()) {
$log->error('Encryption library openssl_pkey_new() fails: ' . openssl_error_string(),
['app' => 'encryption']);
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}
} elseif (openssl_pkey_export($res,
$privateKey,
null,
$this->getOpenSSLConfig())) {
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$keyDetails = openssl_pkey_get_details($res);
$publicKey = $keyDetails['key'];
return [
'publicKey' => $publicKey,
'privateKey' => $privateKey
];
}
$log->error('Encryption library couldn\'t export users private key, please check your servers OpenSSL configuration.' . $this->user,
['app' => 'encryption']);
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if (openssl_error_string()) {
$log->error('Encryption Library:' . openssl_error_string(),
['app' => 'encryption']);
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}
return false;
}
/**
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* Generates a new private key
*
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* @return resource
*/
public function getOpenSSLPKey() {
$config = $this->getOpenSSLConfig();
return openssl_pkey_new($config);
}
/**
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* get openSSL Config
*
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* @return array
*/
private function getOpenSSLConfig() {
$config = ['private_key_bits' => 4096];
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$config = array_merge(
$config,
$this->config->getSystemValue('openssl', [])
);
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return $config;
}
/**
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* @param string $plainContent
* @param string $passPhrase
* @param int $version
* @param int $position
* @return false|string
* @throws EncryptionFailedException
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*/
public function symmetricEncryptFileContent($plainContent, $passPhrase, $version, $position) {
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if (!$plainContent) {
$this->logger->error('Encryption Library, symmetrical encryption failed no content given',
['app' => 'encryption']);
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return false;
}
$iv = $this->generateIv();
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$encryptedContent = $this->encrypt($plainContent,
$iv,
$passPhrase,
$this->getCipher());
// Create a signature based on the key as well as the current version
$sig = $this->createSignature($encryptedContent, $passPhrase.'_'.$version.'_'.$position);
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// combine content to encrypt the IV identifier and actual IV
$catFile = $this->concatIV($encryptedContent, $iv);
$catFile = $this->concatSig($catFile, $sig);
return $this->addPadding($catFile);
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}
/**
* generate header for encrypted file
*
* @param string $keyFormat (can be 'hash' or 'password')
* @return string
* @throws \InvalidArgumentException
*/
public function generateHeader($keyFormat = 'hash') {
if (in_array($keyFormat, $this->supportedKeyFormats, true) === false) {
throw new \InvalidArgumentException('key format "' . $keyFormat . '" is not supported');
}
$cipher = $this->getCipher();
$header = self::HEADER_START
. ':cipher:' . $cipher
. ':keyFormat:' . $keyFormat
. ':' . self::HEADER_END;
return $header;
}
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/**
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* @param string $plainContent
* @param string $iv
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* @param string $passPhrase
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* @param string $cipher
* @return string
* @throws EncryptionFailedException
*/
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private function encrypt($plainContent, $iv, $passPhrase = '', $cipher = self::DEFAULT_CIPHER) {
$encryptedContent = openssl_encrypt($plainContent,
$cipher,
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$passPhrase,
false,
$iv);
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if (!$encryptedContent) {
$error = 'Encryption (symmetric) of content failed';
$this->logger->error($error . openssl_error_string(),
['app' => 'encryption']);
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throw new EncryptionFailedException($error);
}
return $encryptedContent;
}
/**
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* return Cipher either from config.php or the default cipher defined in
* this class
*
* @return string
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*/
public function getCipher() {
$cipher = $this->config->getSystemValue('cipher', self::DEFAULT_CIPHER);
if (!isset($this->supportedCiphersAndKeySize[$cipher])) {
$this->logger->warning(
sprintf(
'Unsupported cipher (%s) defined in config.php supported. Falling back to %s',
$cipher,
self::DEFAULT_CIPHER
),
['app' => 'encryption']);
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$cipher = self::DEFAULT_CIPHER;
}
return $cipher;
}
/**
* get key size depending on the cipher
*
* @param string $cipher
* @return int
* @throws \InvalidArgumentException
*/
protected function getKeySize($cipher) {
if (isset($this->supportedCiphersAndKeySize[$cipher])) {
return $this->supportedCiphersAndKeySize[$cipher];
}
throw new \InvalidArgumentException(
sprintf(
'Unsupported cipher (%s) defined.',
$cipher
)
);
}
/**
* get legacy cipher
*
* @return string
*/
public function getLegacyCipher() {
if (!$this->supportLegacy) {
throw new ServerNotAvailableException('Legacy cipher is no longer supported!');
}
return self::LEGACY_CIPHER;
}
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/**
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* @param string $encryptedContent
* @param string $iv
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* @return string
*/
private function concatIV($encryptedContent, $iv) {
return $encryptedContent . '00iv00' . $iv;
}
/**
* @param string $encryptedContent
* @param string $signature
* @return string
*/
private function concatSig($encryptedContent, $signature) {
return $encryptedContent . '00sig00' . $signature;
}
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/**
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* Note: This is _NOT_ a padding used for encryption purposes. It is solely
* used to achieve the PHP stream size. It has _NOTHING_ to do with the
* encrypted content and is not used in any crypto primitive.
*
* @param string $data
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* @return string
*/
private function addPadding($data) {
return $data . 'xxx';
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}
/**
* generate password hash used to encrypt the users private key
*
* @param string $password
* @param string $cipher
* @param string $uid only used for user keys
* @return string
*/
protected function generatePasswordHash($password, $cipher, $uid = '') {
$instanceId = $this->config->getSystemValue('instanceid');
$instanceSecret = $this->config->getSystemValue('secret');
$salt = hash('sha256', $uid . $instanceId . $instanceSecret, true);
$keySize = $this->getKeySize($cipher);
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$hash = hash_pbkdf2(
'sha256',
$password,
$salt,
100000,
$keySize,
true
);
return $hash;
}
/**
* encrypt private key
*
* @param string $privateKey
* @param string $password
* @param string $uid for regular users, empty for system keys
* @return false|string
*/
public function encryptPrivateKey($privateKey, $password, $uid = '') {
$cipher = $this->getCipher();
$hash = $this->generatePasswordHash($password, $cipher, $uid);
$encryptedKey = $this->symmetricEncryptFileContent(
$privateKey,
$hash,
0,
0
);
return $encryptedKey;
}
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/**
* @param string $privateKey
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* @param string $password
* @param string $uid for regular users, empty for system keys
* @return false|string
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*/
public function decryptPrivateKey($privateKey, $password = '', $uid = '') {
$header = $this->parseHeader($privateKey);
if (isset($header['cipher'])) {
$cipher = $header['cipher'];
} else {
$cipher = $this->getLegacyCipher();
}
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if (isset($header['keyFormat'])) {
$keyFormat = $header['keyFormat'];
} else {
$keyFormat = self::LEGACY_KEY_FORMAT;
}
if ($keyFormat === 'hash') {
$password = $this->generatePasswordHash($password, $cipher, $uid);
}
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// If we found a header we need to remove it from the key we want to decrypt
if (!empty($header)) {
$privateKey = substr($privateKey,
strpos($privateKey,
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self::HEADER_END) + strlen(self::HEADER_END));
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}
$plainKey = $this->symmetricDecryptFileContent(
$privateKey,
$password,
$cipher,
0
);
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if ($this->isValidPrivateKey($plainKey) === false) {
return false;
}
return $plainKey;
}
/**
* check if it is a valid private key
*
* @param string $plainKey
* @return bool
*/
protected function isValidPrivateKey($plainKey) {
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$res = openssl_get_privatekey($plainKey);
// TODO: remove resource check one php7.4 is not longer supported
if (is_resource($res) || (is_object($res) && get_class($res) === 'OpenSSLAsymmetricKey')) {
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$sslInfo = openssl_pkey_get_details($res);
if (isset($sslInfo['key'])) {
return true;
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}
}
return false;
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}
/**
* @param string $keyFileContents
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* @param string $passPhrase
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* @param string $cipher
* @param int $version
* @param int|string $position
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* @return string
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* @throws DecryptionFailedException
*/
public function symmetricDecryptFileContent($keyFileContents, $passPhrase, $cipher = self::DEFAULT_CIPHER, $version = 0, $position = 0) {
if ($keyFileContents == '') {
return '';
}
$catFile = $this->splitMetaData($keyFileContents, $cipher);
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if ($catFile['signature'] !== false) {
try {
// First try the new format
$this->checkSignature($catFile['encrypted'], $passPhrase . '_' . $version . '_' . $position, $catFile['signature']);
} catch (GenericEncryptionException $e) {
// For compatibility with old files check the version without _
$this->checkSignature($catFile['encrypted'], $passPhrase . $version . $position, $catFile['signature']);
}
}
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return $this->decrypt($catFile['encrypted'],
$catFile['iv'],
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$passPhrase,
$cipher);
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}
/**
* check for valid signature
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*
* @param string $data
* @param string $passPhrase
* @param string $expectedSignature
* @throws GenericEncryptionException
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*/
private function checkSignature($data, $passPhrase, $expectedSignature) {
$enforceSignature = !$this->config->getSystemValue('encryption_skip_signature_check', false);
$signature = $this->createSignature($data, $passPhrase);
$isCorrectHash = hash_equals($expectedSignature, $signature);
if (!$isCorrectHash && $enforceSignature) {
throw new GenericEncryptionException('Bad Signature', $this->l->t('Bad Signature'));
} elseif (!$isCorrectHash && !$enforceSignature) {
$this->logger->info("Signature check skipped", ['app' => 'encryption']);
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}
}
/**
* create signature
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*
* @param string $data
* @param string $passPhrase
* @return string
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*/
private function createSignature($data, $passPhrase) {
$passPhrase = hash('sha512', $passPhrase . 'a', true);
return hash_hmac('sha256', $data, $passPhrase);
}
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/**
* remove padding
*
* @param string $padded
* @param bool $hasSignature did the block contain a signature, in this case we use a different padding
* @return string|false
*/
private function removePadding($padded, $hasSignature = false) {
if ($hasSignature === false && substr($padded, -2) === 'xx') {
return substr($padded, 0, -2);
} elseif ($hasSignature === true && substr($padded, -3) === 'xxx') {
return substr($padded, 0, -3);
}
return false;
}
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/**
* split meta data from encrypted file
* Note: for now, we assume that the meta data always start with the iv
* followed by the signature, if available
*
* @param string $catFile
* @param string $cipher
* @return array
*/
private function splitMetaData($catFile, $cipher) {
if ($this->hasSignature($catFile, $cipher)) {
$catFile = $this->removePadding($catFile, true);
$meta = substr($catFile, -93);
$iv = substr($meta, strlen('00iv00'), 16);
$sig = substr($meta, 22 + strlen('00sig00'));
$encrypted = substr($catFile, 0, -93);
} else {
$catFile = $this->removePadding($catFile);
$meta = substr($catFile, -22);
$iv = substr($meta, -16);
$sig = false;
$encrypted = substr($catFile, 0, -22);
}
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return [
'encrypted' => $encrypted,
'iv' => $iv,
'signature' => $sig
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];
}
/**
* check if encrypted block is signed
*
* @param string $catFile
* @param string $cipher
* @return bool
* @throws GenericEncryptionException
*/
private function hasSignature($catFile, $cipher) {
$skipSignatureCheck = $this->config->getSystemValue('encryption_skip_signature_check', false);
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$meta = substr($catFile, -93);
$signaturePosition = strpos($meta, '00sig00');
// If we no longer support the legacy format then everything needs a signature
if (!$skipSignatureCheck && !$this->supportLegacy && $signaturePosition === false) {
throw new GenericEncryptionException('Missing Signature', $this->l->t('Missing Signature'));
}
// enforce signature for the new 'CTR' ciphers
if (!$skipSignatureCheck && $signaturePosition === false && stripos($cipher, 'ctr') !== false) {
throw new GenericEncryptionException('Missing Signature', $this->l->t('Missing Signature'));
}
return ($signaturePosition !== false);
}
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/**
* @param string $encryptedContent
* @param string $iv
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* @param string $passPhrase
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* @param string $cipher
* @return string
* @throws DecryptionFailedException
*/
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private function decrypt($encryptedContent, $iv, $passPhrase = '', $cipher = self::DEFAULT_CIPHER) {
$plainContent = openssl_decrypt($encryptedContent,
$cipher,
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$passPhrase,
false,
$iv);
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if ($plainContent) {
return $plainContent;
} else {
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throw new DecryptionFailedException('Encryption library: Decryption (symmetric) of content failed: ' . openssl_error_string());
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}
}
/**
* @param string $data
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* @return array
*/
protected function parseHeader($data) {
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$result = [];
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if (substr($data, 0, strlen(self::HEADER_START)) === self::HEADER_START) {
$endAt = strpos($data, self::HEADER_END);
$header = substr($data, 0, $endAt + strlen(self::HEADER_END));
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// +1 not to start with an ':' which would result in empty element at the beginning
$exploded = explode(':',
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substr($header, strlen(self::HEADER_START) + 1));
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$element = array_shift($exploded);
while ($element !== self::HEADER_END) {
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$result[$element] = array_shift($exploded);
$element = array_shift($exploded);
}
}
return $result;
}
/**
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* generate initialization vector
*
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* @return string
* @throws GenericEncryptionException
*/
private function generateIv() {
return random_bytes(16);
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}
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/**
* Generate a cryptographically secure pseudo-random 256-bit ASCII key, used
* as file key
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*
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* @return string
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* @throws \Exception
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*/
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public function generateFileKey() {
return random_bytes(32);
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}
/**
* @param $encKeyFile
* @param $shareKey
* @param $privateKey
* @return string
* @throws MultiKeyDecryptException
*/
public function multiKeyDecrypt($encKeyFile, $shareKey, $privateKey) {
if (!$encKeyFile) {
throw new MultiKeyDecryptException('Cannot multikey decrypt empty plain content');
}
if (openssl_open($encKeyFile, $plainContent, $shareKey, $privateKey, 'RC4')) {
return $plainContent;
} else {
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throw new MultiKeyDecryptException('multikeydecrypt with share key failed:' . openssl_error_string());
}
}
/**
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* @param string $plainContent
* @param array $keyFiles
* @return array
* @throws MultiKeyEncryptException
*/
public function multiKeyEncrypt($plainContent, array $keyFiles) {
// openssl_seal returns false without errors if plaincontent is empty
// so trigger our own error
if (empty($plainContent)) {
throw new MultiKeyEncryptException('Cannot multikeyencrypt empty plain content');
}
// Set empty vars to be set by openssl by reference
$sealed = '';
$shareKeys = [];
$mappedShareKeys = [];
if (openssl_seal($plainContent, $sealed, $shareKeys, $keyFiles, 'RC4')) {
$i = 0;
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// Ensure each shareKey is labelled with its corresponding key id
foreach ($keyFiles as $userId => $publicKey) {
$mappedShareKeys[$userId] = $shareKeys[$i];
$i++;
}
return [
'keys' => $mappedShareKeys,
'data' => $sealed
];
} else {
throw new MultiKeyEncryptException('multikeyencryption failed ' . openssl_error_string());
}
}
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}