Comments on "Security Improvement of an RFID Security Protocol of ISO/IEC WD 29167-6"

Song et al. recently scrutinized the security of a mutual authentication protocol published as a part of ISO/IEC WD 29167-6, denoted as Protocol 1, and showed its lack of protection against man-in-the-middle attacks . In addition, they proposed an improved version, called Protocol 1+, and claimed resistance against this sort of attacks. Nevertheless, in this letter we show that the new protocol is as insecure as the original protocol against man-in-the-middle attacks.