1. Security for Measurement Requests and Information
Month 2002
doc.: IEEE /xxxr0
Jan 2004
Security for Measurement Requests and Information
Jon Edney, Nokia Corp.
Dan Harkins, Trapeze Networks
Henry Haverinen, Nokia Corp.
Edney,Haverinen:Nokia, Harkins:Trapeze Networks
John Doe, His Company

2. Jan 2004
Goals
Provide optional confidentiality of TGk information within a group of stations
Provide optional source authentication for unicast action frames
Edney,Haverinen:Nokia, Harkins:Trapeze Networks

3. Problem with only Protecting Action Frames
Jan 2004
Problem with only Protecting Action Frames
Just encrypt Action frames
Use pairwise keys for unicast frames
Use group key for multicast frames
Problem:
Not all TGk information is sent in action frames
Requirement is protect TGk information not just action frames
Edney,Haverinen:Nokia, Harkins:Trapeze Networks

4. Core Assumptions IEEE802.11i is completed as per current draft.
Jan 2004
Core Assumptions
IEEE802.11i is completed as per current draft.
Good keys are available and managed under IEEE802.11i
Information is secret to a group of stations but need not be hidden from other group members
Source authentication and data integrity might be needed for some types of data
Most violations of source authentication and data integrity only result in DOS attack by providing misinformation
Edney,Haverinen:Nokia, Harkins:Trapeze Networks

5. Jan 2004
Flexible approach
Approach allows protection Information Elements separate from delivery method
Approach also allows authentication and integrity protection of Action Frames
IE protection is based on a group key rather than pairwise key
Action Frame protection based on pairwise key for source integrity
Edney,Haverinen:Nokia, Harkins:Trapeze Networks

6. Jan 2004
Concept Summary
Contents of TGk information elements are protected using a group key. This protects against unauthorised disclosure, modification, forgery and replay by non-group member
Contents of unicast TGk Action frame can be optionally protected with pairwise MIC to protect against modification, forgery by group member
Edney,Haverinen:Nokia, Harkins:Trapeze Networks

7. Examples Hiding channel map information in a Probe Response
Jan 2004
Examples
Hiding channel map information in a Probe Response
TGK IE
Probe Response
Probe Response cont…
Broadcast action frame with partly hidden information
Action Frame Hdr
TGK IE
Fully protected unicast action frame
Action Frame Hdr
MIC
TGK IE
Protected by
Group Key
Protected by
Pairwise Key
Unprotected
Other
Edney,Haverinen:Nokia, Harkins:Trapeze Networks

8. Information Elements Four IEs eligible for protection:
Jan 2004
Information Elements
Four IEs eligible for protection:
Measurement Request
Measurement Report
AP Channel Report
Site Report
Edney,Haverinen:Nokia, Harkins:Trapeze Networks

9. General format for “Protectable IEs”
Jan 2004
General format for “Protectable IEs”
New
Same as current draft
Elem ID
Length
Flags
Security Hdr. (opt)
Element Specific Data
Rsvd
Protected
Key ID
ESN0
ESN1
ESN2
ESN3
ESN4
ESN5
b b4 b5
b b7
Protected bit indicates
Whether Security header
is present
ESN = Element Sequence number (increments for each IE generated)
Edney,Haverinen:Nokia, Harkins:Trapeze Networks

10. Protection of IE using CCM
Jan 2004
Protection of IE using CCM
Elem ID
Length
Flags
ESN0-5
Element Specific Data
AAD
Source
MAC (TA)
CCM Processing
Nonce
PIEkey
Elem ID
Length
Flags
ESN0-5
Protected Data
MIC
Note: Use of group key means there is no source integrity. Source MAC address is included to prevent Nonce collisions
Edney,Haverinen:Nokia, Harkins:Trapeze Networks

11. Jan 2004
Replay Protection
PIEkey has group sequence number “Element Sequence Number” (ESN).
Each Station tries to keep value of ESN up to date from received PIEs. This is “Transmit PIE” (TESN)
Each station is given up to date ESN with key on first connection (First TESN)
Possible race condition on transmit by two stations using same ESN
Problem resolved by keeping separate ESN value for each station from which PIEs are received
Edney,Haverinen:Nokia, Harkins:Trapeze Networks

12. Maintaining the TESN Value is initialized from PIEkey key message
Jan 2004
Maintaining the TESN
Value is initialized from PIEkey key message
When receiving valid PIE from other station, if ESN in received frame is greater than TESN then TESN is updated
TESN is increment by one prior to each PIE generation
Edney,Haverinen:Nokia, Harkins:Trapeze Networks

13. ESN Table Keep entry for each other station
Jan 2004
ESN Table
Keep entry for each other station
When receiving PIE from other station check that ESN is greater than last value received
Initialize entry for each other station using own value of TESN
Edney,Haverinen:Nokia, Harkins:Trapeze Networks

14. Action Frames Generic format of action frame
Jan 2004
Action Frames
Generic format of action frame
Category
Action Details
Existing TGk Radio Measurement Format 03
Action
Dlg Tkn
Information Elements
Protected (& unprotected)
Information Elements go here
Proposed TGk Radio Measurement Format 03
Control
Dlg Tkn
MIC (opt)
Information Elements
12 octets
MIC computed over action frame plus TA & RA
Using AES-CBC-MAC-96 – start block as per CCMP
Using Pairwise keys of TA and RA
Prot bit indicates
Whether MIC present
Prot
Action b0
b1 - 7
Edney,Haverinen:Nokia, Harkins:Trapeze Networks

15. Keys Protected Information Element Key (PIEkey)
Jan 2004
Keys
Protected Information Element Key (PIEkey)
Derived for each station from GMK
Delivered using EAPOL-Key message
Must be recomputed when group key updated
MGK = PRF-128(GMK, “Protected IE Expansion”||AA||Nonce)
Measurement Pairwise Key (MPK)
Use existing pairwise keys
Edney,Haverinen:Nokia, Harkins:Trapeze Networks

16. Negotiating Capabilities
Jan 2004
Negotiating Capabilities
New IE indicates PIE capability
Included in beacons and Probe Resp by AP
Indicates whether protected PIE is mandatory
STA includes IE in assoc request if it wants to protect PIEs or not
Edney,Haverinen:Nokia, Harkins:Trapeze Networks

17. Jan 2004
Questions
Edney,Haverinen:Nokia, Harkins:Trapeze Networks

18. Jan 2004
Motion
Move that TGk adopt the security approach described in doc and instruct the editor to incorporate the text of into the TGk draft
Edney,Haverinen:Nokia, Harkins:Trapeze Networks