Simplifying Implementation of CCMP Mode January 2003 Simplifying Implementation of CCMP Mode Jie Liang Texas Instruments Jie Liang, Texas Instruments

Complexity Implications Month 2000 doc.: IEEE 802.11-00/xxx January 2003 Complexity Implications Currently, whole sequence control is included in MIC calculation for CCMP mode Cost: Sequence number can not be determined until right before a STA wins the contention for a chance to transmit Beacon, other management frames change sequence number for data frames Time between the moment a sequence number is determined to its transmission could be PIFS (30us) Throughput requirement for CCMP engine: 2300 bytes/ 30 us = 613 mb/s, usually at most 15 us is available for CCMP (RF turnaround, MAC/PHY delay), the throughput requirement could be >1.2Gbps Precludes other architecture, such as host based encryption, and some micro-controller based hardware implementation Jie Liang, Texas Instruments John Doe, His Company

Month 2000 doc.: IEEE 802.11-00/xxx January 2003 Alternative Solution Include the fragment field in sequence control in MIC calculation, but mute the sequence number field, and require sequential PNs for fragments of same MSDU This should solve the security problem (fragmentation attack) as addressed by including whole Sequence field Attack 1: combine fragments from different MSDU PNs are not sequential Attack 2: combine several continuous MSDU into one MSDU Fragment numbers are all zero Attack 3: swap fragments, adding fragments Protected by fragment number check Jie Liang, Texas Instruments John Doe, His Company

Alternative Solution Benefits: Month 2000 doc.: IEEE 802.11-00/xxx January 2003 Alternative Solution Benefits: Sequence number is dynamic, but fragment number is mostly static Latency requirement is much relaxed Offline, host-based CCMP encryption is supported Much reduction in implementation complexity Satisfy comments from 7 NO votes! Jie Liang, Texas Instruments John Doe, His Company