Abstract. Recently, Wireless Local Area Network (WLAN) is used by enterprises, government, and the military, as well as small office and home offices. Although it is convenient, it has inherent security weaknesses due to wireless characteristics. For this reason, security-sensitive groups are still unwilling to use WLAN. There are several types of attacks to degrade the wireless network throughput using security weakness, especially Protocol Jamming Attacks are critical. These attacks consume little energy and can be easily implemented. In this paper, we introduce Authentication-based Medium Access Control (AMAC) to prevent Virtual Carrier Sense (VCS) Jamming Attack and Deauthentication / Disassociation Jamming Attack that are typical Protocol Jamming Attacks in 802.11 based wireless systems. The proposed scheme can authenticate frames using Universal Hashing Message Authentication Codes (UMAC-32) and Hidden Sequence Number (SN). A-MAC frequently changes the key and SN using shift row ...