Merge pull request #36173 from nextcloud/enh/openssl-seal-custom

Use a PHP implementation of openssl_seal that allows to use modern ciphers

apps/encryption/lib/Crypto/Crypt.php

@@ -6,7 +6,9 @@
  * @author Björn Schießle <bjoern@schiessle.org>
  * @author Christoph Wurst <christoph@winzerhof-wurst.at>
  * @author Clark Tomlinson <fallen013@gmail.com>
+ * @author Côme Chilliet <come.chilliet@nextcloud.com>
  * @author Joas Schilling <coding@schilljs.com>
+ * @author Kevin Niehage <kevin@niehage.name>
  * @author Lukas Reschke <lukas@statuscode.ch>
  * @author Morris Jobke <hey@morrisjobke.de>
  * @author Roeland Jago Douma <roeland@famdouma.nl>
@@ -40,6 +42,7 @@
 use OCP\IL10N;
 use OCP\ILogger;
 use OCP\IUserSession;
+use phpseclib\Crypt\RC4;
 
 /**
  * Class Crypt provides the encryption implementation of the default Nextcloud
@@ -517,12 +520,9 @@ public function symmetricDecryptFileContent($keyFileContents, $passPhrase, $ciph
  /**
  * check for valid signature
  *
- * @param string $data
- * @param string $passPhrase
- * @param string $expectedSignature
  * @throws GenericEncryptionException
  */
- private function checkSignature($data, $passPhrase, $expectedSignature) {
+ private function checkSignature(string $data, string $passPhrase, string $expectedSignature): void {
  $enforceSignature = !$this->config->getSystemValueBool('encryption_skip_signature_check', false);
 
  $signature = $this->createSignature($data, $passPhrase);
@@ -695,9 +695,9 @@ public function generateFileKey() {
  }
 
  /**
- * @param $encKeyFile
- * @param $shareKey
- * @param $privateKey
+ * @param string $encKeyFile
+ * @param string $shareKey
+ * @param \OpenSSLAsymmetricKey|\OpenSSLCertificate|array|string $privateKey
  * @return string
  * @throws MultiKeyDecryptException
  */
@@ -706,7 +706,8 @@ public function multiKeyDecrypt($encKeyFile, $shareKey, $privateKey) {
  throw new MultiKeyDecryptException('Cannot multikey decrypt empty plain content');
  }
 
- if (openssl_open($encKeyFile, $plainContent, $shareKey, $privateKey, 'RC4')) {
+ $plainContent = '';
+ if ($this->opensslOpen($encKeyFile, $plainContent, $shareKey, $privateKey, 'RC4')) {
  return $plainContent;
  } else {
  throw new MultiKeyDecryptException('multikeydecrypt with share key failed:' . openssl_error_string());
@@ -731,7 +732,7 @@ public function multiKeyEncrypt($plainContent, array $keyFiles) {
  $shareKeys = [];
  $mappedShareKeys = [];
 
- if (openssl_seal($plainContent, $sealed, $shareKeys, $keyFiles, 'RC4')) {
+ if ($this->opensslSeal($plainContent, $sealed, $shareKeys, $keyFiles, 'RC4')) {
  $i = 0;
 
  // Ensure each shareKey is labelled with its corresponding key id
@@ -749,7 +750,105 @@ public function multiKeyEncrypt($plainContent, array $keyFiles) {
  }
  }
 
+ /**
+ * returns the value of $useLegacyBase64Encoding
+ *
+ * @return bool
+ */
  public function useLegacyBase64Encoding(): bool {
  return $this->useLegacyBase64Encoding;
  }
+
+ /**
+ * Uses phpseclib RC4 implementation
+ */
+ private function rc4Decrypt(string $data, string $secret): string {
+ $rc4 = new RC4();
+ /** @psalm-suppress InternalMethod */
+ $rc4->setKey($secret);
+
+ return $rc4->decrypt($data);
+ }
+
+ /**
+ * Uses phpseclib RC4 implementation
+ */
+ private function rc4Encrypt(string $data, string $secret): string {
+ $rc4 = new RC4();
+ /** @psalm-suppress InternalMethod */
+ $rc4->setKey($secret);
+
+ return $rc4->encrypt($data);
+ }
+
+ /**
+ * Custom implementation of openssl_open()
+ *
+ * @param \OpenSSLAsymmetricKey|\OpenSSLCertificate|array|string $private_key
+ * @throws DecryptionFailedException
+ */
+ private function opensslOpen(string $data, string &$output, string $encrypted_key, $private_key, string $cipher_algo): bool {
+ $result = false;
+
+ // check if RC4 is used
+ if (strcasecmp($cipher_algo, "rc4") === 0) {
+ // decrypt the intermediate key with RSA
+ if (openssl_private_decrypt($encrypted_key, $intermediate, $private_key, OPENSSL_PKCS1_PADDING)) {
+ // decrypt the file key with the intermediate key
+ // using our own RC4 implementation
+ $output = $this->rc4Decrypt($data, $intermediate);
+ $result = (strlen($output) === strlen($data));
+ }
+ } else {
+ throw new DecryptionFailedException('Unsupported cipher '.$cipher_algo);
+ }
+
+ return $result;
+ }
+
+ /**
+ * Custom implementation of openssl_seal()
+ *
+ * @throws EncryptionFailedException
+ */
+ private function opensslSeal(string $data, string &$sealed_data, array &$encrypted_keys, array $public_key, string $cipher_algo): int|false {
+ $result = false;
+
+ // check if RC4 is used
+ if (strcasecmp($cipher_algo, "rc4") === 0) {
+ // make sure that there is at least one public key to use
+ if (count($public_key) >= 1) {
+ // generate the intermediate key
+ $intermediate = openssl_random_pseudo_bytes(16, $strong_result);
+
+ // check if we got strong random data
+ if ($strong_result) {
+ // encrypt the file key with the intermediate key
+ // using our own RC4 implementation
+ $sealed_data = $this->rc4Encrypt($data, $intermediate);
+ if (strlen($sealed_data) === strlen($data)) {
+ // prepare the encrypted keys
+ $encrypted_keys = [];
+
+ // iterate over the public keys and encrypt the intermediate
+ // for each of them with RSA
+ foreach ($public_key as $tmp_key) {
+ if (openssl_public_encrypt($intermediate, $tmp_output, $tmp_key, OPENSSL_PKCS1_PADDING)) {
+ $encrypted_keys[] = $tmp_output;
+ }
+ }
+
+ // set the result if everything worked fine
+ if (count($public_key) === count($encrypted_keys)) {
+ $result = strlen($sealed_data);
+ }
+ }
+ }
+ }
+ } else {
+ throw new EncryptionFailedException('Unsupported cipher '.$cipher_algo);
+ }
+
+ return $result;
+ }
 }