1. RSC Pools for Mgmt Frames
Month Year
doc.: IEEE yy/xxxxr0
July 2006
RSC Pools for Mgmt Frames
Date: July, 2006
Author:
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K.Hayes
John Doe, Some Company

2. Replay Checking review
Month Year
doc.: IEEE yy/xxxxr0
July 2006
Replay Checking review
With a single session flow, frames must be sent in an ordered sequence across the link – frames cannot be reordered within the session lest security checks declare a replay violation
For multiple sessions, the rule above still holds, but frames may be reordered across sessions (i.e. output scheduling may occur)
K.Hayes
John Doe, Some Company

3. Crypto Transmit Sequencing
July 2006
Crypto Transmit Sequencing
TKIP and CCMP require replay checking as receiver operation
Verification is done with Packet Numbers (PN) built from the IV, extended IV
Transmitter allocates all PNs in the sequence received from the network stack, even for multiple sessions; gaps in the increasing PN sequence are allowed
PNs must never be reused with the same RSN key within the same session
K.Hayes

4. July 2006
What’s a session?
Strictly speaking this is a set of frames with:
A QoS control field with the same TID
- OR-
No QoS control field at all
For TGw, management frames are the second category
There is no QoS control field…and certainly no TID!
Therefore, management frames use the same session as QoS-free data frames
K.Hayes

5. Crypto Receive Sequencing
July 2006
Crypto Receive Sequencing
Multi-session receiver cannot use a single Receive Sequence Counter (RSC) to do replay checks; it must have N counters, where N is the number of sessions
Data frames are “steered” into a discrete RSC bin indexed by their QoS Control Field’s 4-bit TID, or another bin if QoS Control Field is absent from frame header
K.Hayes

6. Management Frame Crypto Construction
July 2006
Management Frame Crypto Construction
Clauses and state frames with no QoS Control field do not include any “priority” in their AAD and shall use 0x00 in their Nonce construction
Management frames have no QoS Control Field in their header and therefore need no “priority octet”
No need to change the 48-bit PN allocation for mgmt frames
It would be incorrect to overload/subvert the MIC/Nonce input field labeled as “priority” with an arbitrary value because uniqueness is already easy to guarantee (and implement)
K.Hayes

7. Guaranteeing Uniqueness with PN
July 2006
Guaranteeing Uniqueness with PN
Transmitter allocates PNs of both mgmt and QoS-free data frames
Simply allocate PNs from the same pool by maintaining a single counter for both!
Using single counter is easiest way to implement this with a single thread
If mgmt and data are transmitted by separate threads/CPUs, then let both threads access a single counter
NO CHANCE of keystream collision since all PNs are unique for all sessions (with or without QoS control field)
Transmitter provides uniqueness across all frames lacking QoS control field
Receiver verifies uniqueness by using a single counter for all frames lacking QoS control field
K.Hayes

8. How can Receiver Guarantee Unique PNs?
July 2006
How can Receiver Guarantee Unique PNs?
Receiver uses a single counter for frames lacking QoS Control field
ALL frames which lack a QoS Control field are checked against a MAC-state counter, just like in i
Receiver performs replay check, just like in i
If attacker is able to inject a frame with no QoS control in the air, receiver will detect it and drop the frame, just like in i
Easy to guarantee, easy to implement, compatible with data cipher suite
K.Hayes

9. July 2006
Questions?
K.Hayes

10. Motion Move to instruct TGw editor to make following changes:
July 2006
Motion
Move to instruct TGw editor to make following changes:
The 0xff value used as input to the TKIP MIC and CCMP MIC for management frames shall be removed from those calculations as in accordance with clause
The 0xff value used as input to the CCMP Nonce for management frames shall be set to 0x00 as in accordance with clause
The PN values used for robust management frames shall be drawn from the same pool as for data frames containing no QoS control field
K.Hayes

11. July 2006
backup
K.Hayes

12. Output Scheduling July 2006 Low Prio PN = 11 PN = 9 Priority Scheduler
Hi Prio
PN = 13
K.Hayes

13. Other examples of MAC state
July 2006
Other examples of MAC state
moreData status
Power Management state
sequence number
fragment number and fragmentation state
MIB variables
Crypto keys
Ad nauseum…
K.Hayes