M. Kassab, A. Belghith, J. Bonnin, S. Sassi Fast Pre-Authentication Based on Proactive Key Distribution for 802.11 Infrastructure Networks M. Kassab, A. Belghith, J. Bonnin, S. Sassi ACM WMuNeP`05 2006/10/31 CS Div. NS Lab. Junbeom Hur

Authentication Server Problem Definition How to reduce the re-authentication latency during handoff in IEEE 802.11 network environment? Authentication Server AP Authentication Re-authentication Station

Fig. 1. IEEE 802.1x Architecture High-speed wireless Internet connectivity Lack of mobility support 802.1x full authentication per handoff : 1000ms 802.11i recommendation – EAP/TLS Obstacle for real-time applications (e.g., 50ms of VoIP) Fig. 1. IEEE 802.1x Architecture

EAP/TLS Authentication PMK = PRF(MK, ‘client EAP encryption’|ClientHello.random|ServerHello.random) PTK = PRF(PMK, ANonce, SNonce, STAmac, APmac) Fig. 2. Complete EAP/TLS Authentication Exchange

Proactive Key Distribution [Arunesh04] Fast handoff Pre-authenticate to the neighbor APs before handoff Fig. 3. Authentication Exchange Process with PKD PMK0 = PRF(MK, ‘client EAP encryption’|ClientHello.random|ServerHello.random) PMKn = PRF(MK, PMKn-1|Apmac|STAmac)

Proposed Method PKD with IAPP caching PKD with anticipated 4-way handshake

PKD with IAPP Caching PKD + IAPP cache mechanism Temporary authentication within a time limit (a) Pre-authentication (b) Re-authentication Fig. 4. Authentication Exchange Process with ‘PKD with IAPP Caching’ PTKx = PRF(PMK, PTKinit|Apmac|STAmac)

PKD with Anticipated 4-Way Handshake 4-way handshake through the current AP (a) Pre-authentication (b) Re-authentication Fig. 5. Authentication Exchange Process with ‘PKD with anticipated 4-way handshake’

Analysis m : # of neighbor APs

Performance Evaluation Test-bed Two STAs associate with an AP 500kb UDP packets with exponential inter-packet time (a) Re-authentication latency (b) Association latency

Discussion PKD with IAPP caching PKD with anticipated 4-way handshake Computation overhead Violation of 802.11i security requirements Mutual authentication and fresh key derivation at each AP No man-in-the-middle attack Security degradation from temporary authentication PKD with anticipated 4-way handshake Communication overhead 2 X (4-way handshake) per neighbor AP Unnecessary PTKs computation Impracticality No support for 802.11f

Conclusion Two methods for PKD-based fast pre-authentication PKD with IAPP caching Temporary authentication Security degradation PKD with anticipated 4-way handshake 4-way handshake during pre-authentication phase Communication / computation overhead