1. March 2007
doc.: IEEE /0354r0
March 2007
Issues in Mesh Header Field Processing in Payload Encryption/Decryption
Date:
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Kyeong Soo (Joseph) Kim, STMicroelectronics
Kyeong Soo (Joseph) Kim, STMicroelectronics

2. March 2007
doc.: IEEE /0354r0
March 2007
Abstract
We summarize technical and non-technical issues in Mesh Header field processing related with payload encryption/decryption.
Kyeong Soo (Joseph) Kim, STMicroelectronics
Kyeong Soo (Joseph) Kim, STMicroelectronics

3. Review of Mesh Data Frame Format
March 2007
doc.: IEEE /0354r0
March 2007
Review of Mesh Data Frame Format
Target of payload encryption/decryption
Octets: 2 2 6 6 6 2
0 or 6 2
4 or 16
0-2312 4
Frame Control
Duration / ID
Address 1
Address 2
Address 3
Sequence Control
Address 4
QoS Control
Mesh Header
Body
FCS
Octets: 2 1 2 12
Mesh Flags
Mesh Addressing
Time To Live (TTL)
Mesh E2E Sequence Number
Bit 0:Address Extension (AE)
Bits 1-7:Reserved for Future Use
Octets: 6: Address 5
6 Address 6
Exists only when the “AE” flag is set to 1.
Kyeong Soo (Joseph) Kim, STMicroelectronics
Kyeong Soo (Joseph) Kim, STMicroelectronics

4. Non-Technical Reasoning behind the Current TGs Approach
March 2007
doc.: IEEE /0354r0
March 2007
Non-Technical Reasoning behind the Current TGs Approach
Many existing security implementations are not flexible enough to support the change of header fields in their processing, i.e., # of offsets from the start of frame header to begin payload encryption/decryption process.
By treating the Mesh Header field as part of a frame body in payload encryption/decryption, we can maximize backward compatibility with the existing security implementations.
Kyeong Soo (Joseph) Kim, STMicroelectronics
Kyeong Soo (Joseph) Kim, STMicroelectronics

5. Review of 802.11 MAC Header Processing
March 2007
doc.: IEEE /0354r0
March 2007
Review of MAC Header Processing
Protocol_Control
Protocol_Control
Defragment / Decrypt
/* Filter valid received frames, updates statstics (counter processing) */
Validate_ MPDU
Filter_ MPDU
Defragment / Decrypt
Filter_MPDU
/* FCS, length & protocol version check */
Validate_MPDU
PHY_SAP_RX
PHY_SAP_RX
* Excerpt from Annex C of Standard
Kyeong Soo (Joseph) Kim, STMicroelectronics
Kyeong Soo (Joseph) Kim, STMicroelectronics

6. Technical Issues in Processing Mesh Header Field as Part of Payload
March 2007
doc.: IEEE /0354r0
March 2007
Technical Issues in Processing Mesh Header Field as Part of Payload
The following are issues resulting from the split in header processing (especially, Filtering_MPDU):
MIB: Possible inconsistency in counter handling (e.g., "dot11CountersEntry") due to the split in header processing.
We may have to split counters as well (i.e., those for regular header fields and new ones for mesh header fields).
Powering: Decryption will be done even for those frames that are to be discarded during Validation/Filtering processes otherwise.
Latency: Alternatively, in case that powering is not an issue, one may try to reduce latency in header processing by pipelining all three subprocesses  Validate, Filter, & Defragment/Decrypt. With the current TGs approach, however, the mesh header processing cannot be even started until the Defragment/Decrypt process has been finished.
Kyeong Soo (Joseph) Kim, STMicroelectronics
Kyeong Soo (Joseph) Kim, STMicroelectronics

7. Split in Header Processing in Current TGs Approach
March 2007
doc.: IEEE /0354r0
March 2007
Split in Header Processing in Current TGs Approach
Protocol_Control
Protocol_Control
Filter_MPDU (2)
/* Based on Mesh Header fields */
Filter_ MPDU (2)
Defragment / Decrypt
Validate_ MPDU
Filter_ MPDU (1)
Defragment / Decrypt
Filter_MPDU (1)
/* Based on regular header fields */
Validate_MPDU
PHY_SAP_RX
PHY_SAP_RX
Kyeong Soo (Joseph) Kim, STMicroelectronics
Kyeong Soo (Joseph) Kim, STMicroelectronics

8. March 2007
doc.: IEEE /0354r0
March 2007
Conclusion
The Mesh Header field should be treated as other fields in the current frame header and therefore not included in payload encryption/decryption.
Kyeong Soo (Joseph) Kim, STMicroelectronics
Kyeong Soo (Joseph) Kim, STMicroelectronics