— Radio Frequency Identification (RFID) systems have provided promising solutions to effective identification of a large number of tagged objects. However, RFID systems suffer from unauthorized tag reading and potential eavesdropping, which becomes a challenging issue because of the shared radio medium and limited size and cost considerations in RFID. In this paper, based on a Linear Congruential Generator (LCG), we propose a lightweight block cipher that can meet the security and performance requirement of RFID systems. The trade-off between the security and overhead is discussed. Based on the proposed block cipher, we further propose a secure protocol for RFID that can provide data confidentiality and mutual authentication between the reader and the tag. We also provide performance analysis of our proposed block cipher.