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5.2 Wireless Communications Security > 5.2.5 Authentication - Pg. 104

104 CHAPTER 5 Mobile Wireless Network Security time complexity of their attack is lower than the brute force attack, but still on the high side, i.e., O(2 105 ), and may not be significantly more practical than the latter. Tews and Beck [12] have developed a Chopchop kind of attack to TKIP-encrypted ARP packets. The attack doesn't recover the temporal key, but decrypts the con- tent of an ARP packet. The attack requires repeatedly resending to the AP, the same packet that needs to be decrypted. The content of the packet is guessed byte by byte starting from the last. The reaction of the AP tells the attacker if he/she guessed right. At this time, it is hard to claim that the level of difficulty of attacks on TKIP remains strong. Progress has been made. Motivation is high among researchers to break TKIP because of potential recognition of peers. It is likely that an eavesdropping attack on TKIP will eventually succeed. One needs to monitor the TKIP cracking progress. Key Counter n bits from message Block cipher encryption n bits XOR n bits encrypted message FIGURE 5-3 CCMP encryption. traffic is strong and unlikely to happen at this