Adds type hinting for scalar types in ICrypto->decrypt

Signed-off-by: Morris Jobke <hey@morrisjobke.de>

lib/private/Security/Crypto.php

@@ -108,7 +108,7 @@ class Crypto implements ICrypto {
 	 * @return string plaintext
 	 * @throws \Exception If the HMAC does not match
 	 */
-	public function decrypt($authenticatedCiphertext, $password = '') {
+	public function decrypt(string $authenticatedCiphertext, string $password = ''): string {
 		if($password === '') {
 			$password = $this->config->getSystemValue('secret');
 		}

lib/public/Security/ICrypto.php

@@ -61,5 +61,5 @@ interface ICrypto {
 	 * @throws \Exception If the HMAC does not match
 	 * @since 8.0.0
 	 */
-	public function decrypt($authenticatedCiphertext, $password = '');
+	public function decrypt(string $authenticatedCiphertext, string $password = ''): string;
 }