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 <[email protected]>
  * @author Christoph Wurst <[email protected]>
  * @author Clark Tomlinson <[email protected]>
+ * @author Côme Chilliet <[email protected]>
  * @author Joas Schilling <[email protected]>
+ * @author Kevin Niehage <[email protected]>
  * @author Lukas Reschke <[email protected]>
  * @author Morris Jobke <[email protected]>
  * @author Roeland Jago Douma <[email protected]>
@@ -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;
+	}
 }