Lightweight protocol for anonymity and mutual authentication in RFID systems Radio Frequency Identification (RFID) technology is rapidly making its way to next generation automatic identification systems. Despite encouraging prospects of RFID technology, security threats and privacy concerns limit its widespread deployment. Security in passive RFID tag based systems is a challenge owing to the severe resource restrictions. In this paper, we present a lightweight anonymity / mutual authentication protocol that uses a unique choice of pseudorandom numbers to achieve basic security goals, i.e. confidentiality, integrity and authentication. We validate our protocol by security analysis.