Date Added: Apr 2011
RFID is popular to be used in plenty of applications with its capability of remote automatic identification. However, information transmitted wirelessly is under the treats of eavesdropping, interception, or modification because of the nature of the transmission media. Thus, Yeh et al. proposed an RFID authentication scheme based on quadratic residues by improving Chen et al.'s. However, the authors find that the server needs to maintain the obsolete shared secret key to resist DoS (Denial of Service) attack in both schemes.