In this work we present a new methodology for preventing de-synchronization attacks over the SASI ultra-lightweight authentication protocol. The methodology is based on securing the communication channel between the tag and the reader. We modify in the original protocol authentication phase so that minimizing the probability of fooling out the reader with invalid tags. One of the benefits of this methodology is keeping the communication cost for the original SASI protocol as is while achieving better secured solution. The proposed methodology doesn't affect the cost of messaging exchange between the tag and the reader. However, there is slight increasing in storage overhead. We also present results that show the effectiveness of the modified protocol on the overall all RFID system performance.