On the security of RFID anti-counting security protocol (ACSP)

Recently Qian et al. (2012)  [26] have proposed a new attack for RFID systems, called counting attack, where the attacker just aims to estimate the number of tagged objects instead of steal the tags' private information. They have stated that most of the existing RFID mutual authentication protocols are vulnerable to this attack. To defend against counting attack, they proposed a novel Anti-Counting Security Protocol called ACSP. The designers of ACSP have claimed that their protocol is resistant against counting attack and also the other known RFID security threats. However in this paper we present the following efficient attacks against this protocol: