1. Overview of Key Holder Security Association Teardown Mechanism
September 2007
doc.: IEEE /2376r0
September 2007
Overview of Key Holder Security Association Teardown Mechanism
Date:
Authors:
Steve Emeott, Motorola
Steve Emeott, Motorola

2. September 2007
doc.: IEEE /2376r0
September 2007
Abstract
This submission provides an overview of document 11-07/2372r0, which proposes a protocol for tearing down a mesh key holder security association that had been set up between a mesh authenticator and a mesh key distributor
Steve Emeott, Motorola
Steve Emeott, Motorola

3. Outline Overview Discussion of questions received
September 2007
doc.: IEEE /2376r0
September 2007
Outline
Overview
Mesh Key Holder Security Associations
Teardown Mechanism
Discussion of questions received
Steve Emeott, Motorola
Steve Emeott, Motorola

4. Mesh Key Holder Security Association
September 2007
Mesh Key Holder Security Association
A MP is elevated to a Mesh Authenticator after establishing a Mesh Key Holder Security Association (MKHSA) with an MKD
A MKHSA between an MA and its MKD is identified by
MPTK-KDShortName
The MKHSA state consists of
MPTK-KD (session key)
Key Replay Counters
If an MP moves to a new MKD domain, it should attempt to tear down the MKHSA in its old domain
Allows the MKD to delete old state
mesh key distributor
mesh authenticator
Mesh Key Holder Security Handshake message 1
Mesh Key Holder Security Handshake message 2
Mesh Key Holder Security Handshake message 3
Mesh Key Holder Security Handshake message 4
Figure: Mesh Key Holder Security Association Handshake
Steve Emeott, Motorola

5. Example of MA behavior when changing MKD domains
September 2007
Example of MA behavior when changing MKD domains
MKD 1
MA 1
MA3
MKD 2 MA 2
Initial MSA Authentication
In MKDD 1
Key Holder Security HS
Initial MSA Authentication
Proposed in 07/2372
Key Holder Security HS
Key Holder Security Teardown
In MKDD 2
After the Key Holder Security Teardown, MA3 has a secure peer link with both MA1 and MA2, but it only has a MKHSA with MKD2.
Steve Emeott, Motorola

6. Key Holder Security Teardown protocol details
September 2007
Key Holder Security Teardown protocol details
Either MA or MKD may initiate
The MKHSA torn down is identified by MPTK-KDShortName
The teardown allows the MKD and MA to clean up state
The Key Holder Security Teardown protocol permits the MA to delete a prior session, when joining a new MKD domain.
The protocol may also be used by an MKD if it must stop its services as an MKD to one or more MAs.
Requester
Responder
Teardown Request
Teardown Response
Steve Emeott, Motorola

7. Earlier Questions Received
September 2007
Earlier Questions Received
Question: What happens if the MA initiates a new security session while the MKD is tearing down a pre-existing security association? Can this lead to livelock, where one side keeps proposing a new security association and the other tears it down
Answer: The MKHSA to be torn down is identified in the teardown request message by its MPTK-KDShortName, which will be different than the identifier for the new security session. Of course, the MKD is free to accept or decline a request for the new session
Steve Emeott, Motorola

8. Earlier Questions Received (cont.)
September 2007
Earlier Questions Received (cont.)
Question: How does it work if the MA and MKD both initiate the teardown simultaneously.
Answer: protocol supports timeout and retry features to increase the probability of success
Any party sending a teardown request starts a timer, waits for response. When the timer expires it may retransmit request
If a teardown response is not received after the teardown retransmission limit is reached, the MKHSA is deleted.
Any party receiving a teardown request sends out a teardown response and starts a timer. The identified MKHSA is deleted when the timer expires.
Any party receiving a duplicate request while decrementing the timer should send out a duplicate response
When a party receives a valid response after sending out a teardown request, it deletes the identified MKHSA
Any party receiving a teardown request while waiting for a response to its own teardown request for the same MKHSA should send a teardown response
Steve Emeott, Motorola