Grouping proof for RFID tags

An RFID tag is a small and cheap device which is combined in IC chip and an antenna for radio communications. The tag is used for management of goods and its distribution. Moreover it reduces the cost of managements of goods. However, an RFID system has some security problems. Juels proposed a "yoking-proof" which guarantees the existence of two tags (Juels, 2004). But we point out that this scheme is not secure against a replay attack. In this paper, we propose a scheme which deals with the problem by using time stamp. Moreover, we propose a scheme which guarantees the existence of a group of RFID tags.