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

2. Complexity Implications
Month 2000
doc.: IEEE /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

3. Month 2000
doc.: IEEE /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

4. Alternative Solution Benefits:
Month 2000
doc.: IEEE /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