Wireless Security

Access Networks Core Networks The Current Internet: Connectivity and Processing Transit Net Private Peering NAP Public Peering PSTN Regional Wireline Regional Voice Cell Cable Modem LAN Premises- based WLAN Premises- based Operator- based H.323 Data RAS Analog DSLAM H.323

How can it affect cell phones? r Cabir worm can infect a cell phone m Infect phones running Symbian OS m Started in Philippines at the end of 2004, surfaced in Asia, Latin America, Europe, and recently in US m Posing as a security management utility m Once infected, propagate itself to other phones via Bluetooth wireless connections m Symbian officials said security was a high priority of the latest software, Symbian OS Version 9. r With ubiquitous Internet connections, more severe viruses/worms for mobile devices will happen soon …

Outlines r Basics r Mobile link access: CDMA/CA r Security in b r Example and more attacks r Trend: Wireless MAN

IEEE Wireless LAN r b m GHz unlicensed radio spectrum m up to 11 Mbps m widely deployed, using base stations r a m 5-6 GHz range m up to 54 Mbps r g m GHz range m up to 54 Mbps r All use CSMA/CA for multiple access r All have base-station and ad-hoc network versions

Base station approch r Wireless host communicates with a base station m base station = access point (AP) r Basic Service Set (BSS) (a.k.a. “cell”) contains: m wireless hosts m access point (AP): base station r BSS’s combined to form distribution system (DS)

Ad Hoc Network approach r No AP (i.e., base station) r wireless hosts communicate with each other m to get packet from wireless host A to B may need to route through wireless hosts X,Y,Z r Applications: m “laptop” meeting in conference room, car m interconnection of “personal” devices m battlefield

CSMA (Carrier Sense Multiple Access) CSMA: listen before transmit: r If channel sensed idle: transmit entire frame r If channel sensed busy, defer transmission r Human analogy: don’t interrupt others!

CSMA collisions collisions can still occur: propagation delay means two nodes may not hear each other’s transmission collision: entire packet transmission time wasted spatial layout of nodes note: role of distance & propagation delay in determining collision probability

CSMA/CD (Collision Detection) CSMA/CD: carrier sensing, deferral as in CSMA m collisions detected within short time m colliding transmissions aborted, reducing channel wastage r collision detection: m easy in wired LANs: measure signal strengths, compare transmitted, received signals m difficult in wireless LANs: receiver shut off while transmitting r human analogy: the polite conversationalist

CSMA/CD collision detection

IEEE : multiple access r Collision if 2 or more nodes transmit at same time r CSMA makes sense: m get all the bandwidth if you’re the only one transmitting m shouldn’t cause a collision if you sense another transmission r Collision detection doesn’t work: hidden terminal problem

IEEE MAC Protocol: CSMA/CA CSMA: sender - if sense channel idle for DISF sec. then transmit entire frame (no collision detection) -if sense channel busy then binary backoff CSMA receiver - if received OK return ACK after SIFS (ACK is needed due to hidden terminal problem)

Collision avoidance mechanisms r Problem: m two nodes, hidden from each other, transmit complete frames to base station m wasted bandwidth for long duration ! r Solution: m small reservation packets m nodes track reservation interval with internal “network allocation vector” (NAV)

Collision Avoidance: RTS-CTS exchange r sender transmits short RTS (request to send) packet: indicates duration of transmission r receiver replies with short CTS (clear to send) packet m notifying (possibly hidden) nodes r hidden nodes will not transmit for specified duration: NAV

Collision Avoidance: RTS-CTS exchange r RTS and CTS short: m collisions less likely, of shorter duration m end result similar to collision detection r IEEE allows: m CSMA m CSMA/CA: reservations m polling from AP

Outlines r Basics r Mobile link access: CDMA/CA r Security in b r Example and more attacks r Trend: Wireless MAN

802.11b: Built in Security Features r Service Set Identifier (SSID) r Differentiates one access point from another r SSID is cast in ‘beacon frames’ every few seconds. r Beacon frames are in plain text!

Associating with the AP r Access points have two ways of initiating communication with a client r Shared Key or Open Key authentication r Open key: need to supply the correct SSID m Allow anyone to start a conversation with the AP r Shared Key is supposed to add an extra layer of security by requiring authentication info as soon as one associates

How Shared Key Auth. works r Client begins by sending an association request to the AP r AP responds with a challenge text (unencrypted) r Client, using the proper WEP key, encrypts text and sends it back to the AP r If properly encrypted, AP allows communication with the client

Wired Equivalent Protocol (WEP) r Primary built security for protocol r Uses 40bit RC4 encryption r Intended to make wireless as secure as a wired network r Unfortunately, since ratification of the standard, RC4 has been proven insecure, leaving the protocol wide open for attack

Case study of a non-trivial attack r Target Network: a large, very active university based WLAN r Tools used against network: m Laptop running Red Hat Linux v.7.3, m Orinoco chipset based b NIC card m Patched Orinoco drivers m Netstumbler Netstumbler can not only monitor all active networks in the area, but it also integrates with a GPS to map AP’s m Airsnort Passively listen to the traffic r NIC drivers MUST be patched to allow Monitor mode (listen to raw b packets)

Assessing the Network r Using Netstumbler, the attacker locates a strong signal on the target WLAN r WLAN has no broadcasted SSID r Multiple access points r Many active users r Open authentication method r WLAN is encrypted with 40bit WEP

Cracking the WEP key r Attacker sets NIC drivers to Monitor Mode r Begins capturing packets with Airsnort r Airsnort quickly determines the SSID r Sessions can be saved in Airsnort, and continued at a later date so you don’t have to stay in one place for hours r A few 1.5 hour sessions yield the encryption key r Once the WEP key is cracked and his NIC is configured appropriately, the attacker is assigned an IP, and can access the WLAN

More Attacks in Wireless Networks r Rogue Access Point m Solution: Monitor the air space for unexpected AP r Radio Frequency (RF) Interference r AP Impersonation m Rogue AP spoofs its MAC address to the identity of an authorized AP m Man-in-the-middle attack m Denial of service attack

Outlines r Basics r Mobile link access: CDMA/CA r Security in b r Example and more attacks r Trend: Wireless MAN

IEEE WirelessMAN Standard for Broadband Wireless Metropolitan Area Networks r Broad bandwidth m Up to 134 Mbps in GHz band r Comprehensive and modern security m Packet data encryption DES and AES used m Key management protocol Use RSA to set up a shared secret between subscriber station and base station Use the secret for subsequent exchange of traffic encryption keys (TEK)

Backup Slides

Summary of MAC protocols r What do you do with a shared media? m Channel Partitioning, by time, frequency or code Time Division,Code Division, Frequency Division m Random partitioning (dynamic), ALOHA, CSMA, CSMA/CD carrier sensing: easy in some technologies (wire), hard in others (wireless) CSMA/CD used in Ethernet