Radio frequency identification (RFID) has been widely deployed for manufacturing, supply chain management, etc. Unfortunately, RFID may cause privacy and security problems. To solve these problems, researchers have studied extensively on RFID security systems. Ateniese et al. proposed an RFID protocol using insubvertible encryption based on the universal re-encryption. Although this protocol achieves the integrity of ciphertexts randomized by authorized users, it still leaves security problems. In this paper, we propose a secure RFID protocol based on insubvertible encryption involving guardian proxy. The guardian proxy is a personal RFID-privacy device which may be integrated into cellular phones or PDAs. By introducing the guardian proxy and other basic cryptographic primitives into RFID systems, our protocol is secure against the tag spoofing and swapping attacks. Moreover, our protocol enables ownership transfer.