public function getKey(PKEncryptionEnabledUserInterface $user)
    {
        $userClass = $this->getUserClass($user);
        $userId = $user->getId();

        return isset($this->encryptedKeys[$userClass]) && isset($this->encryptedKeys[$userClass][$userId])
            ? $this->encryptedKeys[$userClass][$userId]
            : null;
    }