Wireless Security

Wireless Security

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

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

Outlines • 802.11 Basics • Mobile link access: CDMA/CA • Security in 802.11b • Example and more attacks • Trend: 802.16 Wireless MAN

802.11b 2.4-5 GHz unlicensed radio spectrum up to 11 Mbps widely deployed, using base stations 802.11a 5-6 GHz range up to 54 Mbps 802.11g 2.4-5 GHz range up to 54 Mbps All use CSMA/CA for multiple access All have base-station and ad-hoc network versions IEEE 802.11 Wireless LAN

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

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

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

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

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

CSMA/CD collision detection

IEEE 802.11: multiple access • Collision if 2 or more nodes transmit at same time • CSMA makes sense: • get all the bandwidth if you’re the only one transmitting • shouldn’t cause a collision if you sense another transmission • Collision detection doesn’t work: hidden terminal problem

IEEE 802.11 MAC Protocol: CSMA/CA 802.11 CSMA: sender - if sense channel idle for DISF sec. then transmit entire frame (no collision detection) -if sense channel busy then binary backoff 802.11 CSMA receiver - if received OK return ACK after SIFS (ACK is needed due to hidden terminal problem)

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

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

Collision Avoidance: RTS-CTS exchange • RTS and CTS short: • collisions less likely, of shorter duration • end result similar to collision detection • IEEE 802.11 allows: • CSMA • CSMA/CA: reservations • polling from AP

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

Associating with the AP • Access points have two ways of initiating communication with a client • Shared Key or Open Key authentication • Open key: need to supply the correct SSID • Allow anyone to start a conversation with the AP • 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 • Client begins by sending an association request to the AP • AP responds with a challenge text (unencrypted) • Client, using the proper WEP key, encrypts text and sends it back to the AP • If properly encrypted, AP allows communication with the client

Wired Equivalent Protocol (WEP) • Primary built security for 802.11 protocol • Uses 40bit RC4 encryption • Intended to make wireless as secure as a wired network • Unfortunately, since ratification of the 802.11 standard, RC4 has been proven insecure, leaving the 802.11 protocol wide open for attack

Case study of a non-trivial attack • Target Network: a large, very active university based WLAN • Tools used against network: • Laptop running Red Hat Linux v.7.3, • Orinoco chipset based 802.11b NIC card • Patched Orinoco drivers • Netstumbler • Netstumbler can not only monitor all active networks in the area, but it also integrates with a GPS to map AP’s • Airsnort • Passively listen to the traffic • NIC drivers MUST be patched to allow Monitor mode (listen to raw 802.11b packets)

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

Cracking the WEP key • Attacker sets NIC drivers to Monitor Mode • Begins capturing packets with Airsnort • Airsnort quickly determines the SSID • Sessions can be saved in Airsnort, and continued at a later date so you don’t have to stay in one place for hours • A few 1.5 hour sessions yield the encryption key • 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 • Rogue Access Point • Solution: Monitor the air space for unexpected AP • Radio Frequency (RF) Interference • AP Impersonation • Rogue AP spoofs its MAC address to the identity of an authorized AP • Man-in-the-middle attack • Denial of service attack

IEEE 802.16 WirelessMAN Standard for Broadband Wireless Metropolitan Area Networks • Broad bandwidth • Up to 134 Mbps in 10-66 GHz band • Comprehensive and modern security • Packet data encryption • DES and AES used • 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 • What do you do with a shared media? • Channel Partitioning, by time, frequency or code • Time Division,Code Division, Frequency Division • Random partitioning (dynamic), • ALOHA, CSMA, CSMA/CD • carrier sensing: easy in some technologies (wire), hard in others (wireless) • CSMA/CD used in Ethernet

Wireless Security