TKIP (Temporal Key Integrity Protocol) was introduced with WPA to enhance WEP security. One of the security mechanisms used in TKIP is a per-MPDU (MAC Protocol Data Unit) sequence counter called the TSC (TKIP Sequence Counter). The TSC acts as a form of replay protection by assigning a unique sequence number to each transmitted frame. If a packet is received with a sequence number lower than or equal to a previously received number, it is discarded. This directly prevents replay attacks, where a malicious actor resends previously captured frames in an attempt to spoof the session or extract data.
[References:, , CWSP-208 Official Study Guide, Chapter 5 (WLAN Threats and Attacks), , CWNP Exam Objectives: WLAN Encryption and Key Management, , IEEE 802.11i-2004 standard (Replay protection mechanisms in TKIP)]
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