Due to the stringent computational capabilities of low-cost RFID tags, several lightweight secure authentication protocols have been proposed for an RFID-based supply chain using bitwise operations. In this paper, we study the vulnerabilities associated with bitwise operations by doing cryptanalysis of a secure lightweight authentication protocol for RFID tags. The bitwise operations like rotation and XOR show that the protocol is vulnerable to tag, reader, and supply chain node impersonation attacks. We find that the major cause of the vulnerability is bitwise operations and suggest using the physically unclonable functions rather than bitwise operations to secure such lightweight protocols.