public function addKey(PKEncryptionEnabledUserInterface $user, $encryptedKey)
    {
        $userClass = $this->getUserClass($user);
        $userId = $user->getId();
        if (!isset($this->encryptedKeys[$userClass])) {
            $this->encryptedKeys[$userClass] = array();
        }
        $this->encryptedKeys[$userClass][$userId] = $encryptedKey;
    }