1. Extra MIC for use in Public Access WLAN
Month 2002
doc.: IEEE /xxxr0
May 2002
Extra MIC for use in Public Access WLAN
Stefan Rommer, Mats Näslund
(Ericsson)
Stefan Rommer, Mats Näslund (Ericsson)
John Doe, His Company

2. May 2002
Motivation
Public Access WLAN has special properties not present in corporate WLAN.
Security in the AP and between the AP and a WLAN Serving Node (WSN) is important.
Public Access Hotspot AP
WSN/FA AP
Could be highly untrusted!
Stefan Rommer, Mats Näslund (Ericsson)

3. Motivation (2) Operators are very concerned about robust billing.
May 2002
Motivation (2)
Operators are very concerned about robust billing.
Robust billing requires at least integrity protection between mobile terminal and WSN.
Public Access Hotspot
Billing data collected here AP
WSN/FA AP
Could be highly untrusted!
Stefan Rommer, Mats Näslund (Ericsson)

4. Solution alternatives
Month 2002
doc.: IEEE /xxxr0
May 2002
Solution alternatives
Extend the i security association (authentication, encryption etc.) from the Mobile all the way to the WSN.
Difficult since i is closely tied to the MAC layer.
Let higher layers and/or other standards perform the needed functions
A layer-2 solution is to prefer.
IEEE is not well supported.
Use proprietary solutions
Not good for interoperability and market acceptance
Add needed functions to i
Stefan Rommer, Mats Näslund (Ericsson)
John Doe, His Company

5. Add needed functions to 802.11i: Extra MIC
May 2002
Add needed functions to i: Extra MIC
Add a (optional) ’transparent’ MIC that is not closely tied to the MAC layer
MIC calculated over the whole payload (MSDU)
Payload’ = Payload || extra MIC
The AP can be configured to not add/verify the MIC
The AP can transparently forward the Payload || MIC
Stefan Rommer, Mats Näslund (Ericsson)

6. Possible message flow 802.11i MIC’ Basic 802.11i Payload’
May 2002
Possible message flow
802.11i MIC’
Basic i AP
WSN/FA
Payload’ RC
Payload
MIC’
TAG
Payload
MIC’
Payload
AES Encrypted IV
Payload
MIC’
Michael
ICV
TKIP Encrypted
Stefan Rommer, Mats Näslund (Ericsson)

7. Motivation (3): Why specify it in 802.11i?
May 2002
Motivation (3): Why specify it in i?
A single standardised WLAN-solution will promote interoperability.
Possible to reuse existing i functions, e.g. the key management.
Possible to reuse the existing algorithms (e.g. Michael).
Stefan Rommer, Mats Näslund (Ericsson)

8. May 2002
Key details AP
WSN
Trusted RADIUS
Trusted RADIUS
WSN acts as a RADIUS Proxy and can extract the EAP Master Key.
A key for the new MIC can then be derived both at the Mobile and at the WSN.
Stefan Rommer, Mats Näslund (Ericsson)

9. Can we use the existing 802.11i MICs instead of adding a new one?
May 2002
Can we use the existing i MICs instead of adding a new one?
Add MIC in the WSN, do the encryption in the AP.
MIC should be applied to whole MSDU
TKIP:
Should be possible to add Michael in the WSN
AES:
OCB: Not easy, encryption and authentication coupled.
CCM: Add CBC-MAC in WSN.
Stefan Rommer, Mats Näslund (Ericsson)

10. Conclusions Public access sites need “extended” protection.
May 2002
Conclusions
Public access sites need “extended” protection.
Robust billing requires at least integrity protection.
An extra MIC is one option.
802.11i has the possibility to provide it.
Existing security functions can be reused.
Stefan Rommer, Mats Näslund (Ericsson)