Security and Wireless LANs Or Fun and Profit With Your Neighbor’s Bandwidth Chris Murphy MIT Information Systems

The Problem Wireless LANs broadcast your network connections Radio doesn’t care about firewalls Data can be captured without physical access Network resources can be hijacked

802.11 Protocol Family 802.11 – 2.4Ghz, 2Mbit specification 802.11a – 5Ghz, 54Mbit specification 802.11b – 2.4Ghz, 11Mbit specification Currently the predominant, available technology 802.11d – regulatory issues 802.11e – addresses QoS 802.11f – inter-access-point protocols 802.11g – 2.4Ghz, ~20Mbit specification 802.11h – frequency allocation 802.11i - security

The Solution? Access Control Data Encryption By MAC addresses By network names (SSID) Data Encryption WEP (Wired Equivalent Privacy) Can also be used for access control All these schemes have limits and flaws

MAC Address Access Control Access Points have a list of allowed MAC addresses Often stored in each Access Point Limited to about 500 addresses Some products use a server-based list, using systems like RADIUS Easily defeated by sniffing for an allowed address

SSID Access Control Normally, the SSID is broadcast in beacon packets A “closed” network does not include the SSID in beacons NOT part of the 802.11 standard Has a fatal flaw…..

Normal open network

“Closed” network (SSID “PEAKABOO”)

Now a client wants to join the network…..

…and an access point responds.

Data Encryption WEP – Wired Equivalent Privacy 40 bit RC4, 128 bit optional Most APs support up to 4 keys How do you manage keys in a large organization? This assumes all users are “good guys”

Data Encryption A group at Berkeley has published some flaws in WEP http://www.isaac.cs.berkeley.edu/isaac/wep-faq.html Outlines a number of design flaws in WEP A number of (currently theoretical) attacks are outlined in the referenced document A response from the IEEE 802.11 group chair is available at http://www.wi-fi.com/pdf/Wi-FiWEPSecurity.pdf

LANs – Standards – 802.11 Security Scott Fluhrer, Itsik Mantin, and Adi Shamir have identified weaknesses in the RC4 algorithm used by WEP Attack only requires cyphertext On the order of 100Mb – 1Gb needed Compute time scales linearly with key size The paper is available at http://www.eyetap.org/~rguerra/toronto2001/rc4_ksaproc.pdf An implementation of this attack is available at http://airsnort.sourceforge.net/

Spread Spectrum as Security? Spread Spectrum technology, while touted as difficult to intercept, offers little here as NICs are preprogrammed with the spreading sequences and can talk to each other out of the box.

So What Are Our Options? While flawed, the described methods can provide some protection from casual abuse Treat wireless clients as remote clients Place APs outside firewalls Use VPNs to access internal network And as always, use secure protocols

Future Wireless Security 802.11i should provide a standards-based path for actual user authentication, and negotiation of user and session specific encryption keys This group is working in conjunction with the 802.1x group, relating to per-port network access control