Today Radio Frequency Identification (RFID) technologies are applied in many fields for a variety of applications. Though bringing great productivity gains, RFID systems may cause new security and privacy threats to individuals or organizations. Therefore, it is important to protect the security of RFID systems and the privacy of RFID tag owners. Unfortunately, none of the existing solutions provide a complete defense against eavesdroppers who could monitor the communication between RFID readers and tags and recover the contents of tags. Based on our research, we propose two novel RFID backward channel protection protocols, namely dynamic bit encoding and optimized dynamic bit encoding. Our schemes are able to achieve high anonymity with limited communication overhead. Our extensive simulations show that both proposed schemes provide much stronger backward channel protection than existing techniques. In addition, analytical models were created and validated through comparisons with simulation results.