Abstract Since Low-cost RFID tags have very limited hardware resources, it is difficult to implement an authentication protocol which uses heavy operations such as modern ciphers or hash functions. It has been presented some ultra-lightweight RFID authentication protocols for low-cost RFID tags by using very light operations. Recently, Jeon and Yoon proposed a new ultra-lightweight RFID authentication protocol. They defined and used the merge and separation operations. The merge operation can merge the bits from two bit strings and the separation operation is an inverse operation of the merge operation. However, we found that the protocol cannot serve correctly when the collision of tag pseudonyms is occurred. In this paper, we propose an improved authentication protocol that solves the problem. We show that the proposed protocol can resist various security attacks and is efficient enough to implement low-cost RFID tags
