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Security Issues in 802.11 Wireless Networks. Prabhaker Mateti Wright State University www.wright.edu/~pmateti. Talk Outline. Wireless LAN Overview Wireless Network Sniffing Wireless Spoofing Wireless Network Probing AP Weaknesses Denial of Service Man-in-the-Middle Attacks War Driving

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Security Issues in 802.11 Wireless Networks


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    1. Security Issues in 802.11 Wireless Networks Prabhaker Mateti Wright State University www.wright.edu/~pmateti

    2. Talk Outline • Wireless LAN Overview • Wireless Network Sniffing • Wireless Spoofing • Wireless Network Probing • AP Weaknesses • Denial of Service • Man-in-the-Middle Attacks • War Driving • Wireless Security Best Practices • Conclusion WiFi Security

    3. Ack • This talk is an overview of what has been known for a couple of years. • Figures borrowed from many sources on the www. • Apologies that I lost track of the original sources. WiFi Security

    4. This talk is based on … • Prabhaker Mateti, “Hacking Techniques in Wireless Networks”, in The Handbook of Information Security, Editor: Bidgoli, John Wiley, 2005 • www.wright.edu/~pmateti/InternetSecurity/ WiFi Security

    5. Wireless LAN Overview Without security issues

    6. OSI Model Application Presentation Session Transport Network Data Link 802.11 MAC header 802.11 Physical 802.11 PLCP header WiFi Security

    7. IEEE 802.11 • Published in June 1997 • 2.4GHz operating frequency • 1 to 2 Mbps throughput • Can choose between frequency hopping or direct sequence spread modulation WiFi Security

    8. IEEE 802.11b • 1999 • Data Rate: 11 Mbps • Reality: 5 to 7 Mbps • 2.4-Ghz band; runs on 3 channels • shared by cordless phones, microwave ovens, and many Bluetooth products • Only direct sequence modulation is specified • Most widely deployed today WiFi Security

    9. IEEE 802.11a • Data Rate: 54 Mbps • Reality: 25 to 27 Mbps • Runs on 12 channels • Not backward compatible with 802.11b • Uses Orthogonal Frequency Division Multiplexing (OFDM) WiFi Security

    10. IEEE 802.11g • An extension to 802.11b • Data rate: 54 Mbps • 2.4-Ghz band WiFi Security

    11. IEEE 802.11n • An extension to 802.11a/b/g • Final draft expected in 2010 • Data rate: 600 Mbps • 2.4-Ghz band WiFi Security

    12. 802 .11 Terminology: Station (STA) • Device that contains IEEE 802.11 conformant MAC and PHY interface to the wireless medium, but does not provide access to a distribution system • Most often end-stations available in terminals (work-stations, laptops etc.) • Typically Implemented in a PC-Card • Built into recent laptops and PDAs WiFi Security

    13. PC-Card Hardware Radio Hardware 802.11 frame format WMAC controller with Station Firmware (WNIC-STA) 802.3 frame format Platform Computer Driver Software (STADr) Ethernet V2.0 / 802.3 frame format Protocol Stack Station Architecture • Ethernet-like driver interface • supports virtually all protocol stacks • Frame translation according to IEEE 802.1H • Ethernet Types 8137 (Novell IPX) and 80F3 (AARP) encapsulated via the Bridge Tunnel encapsulation scheme • IEEE 802.3 frames: translated to 802.11 • All other Ethernet Types: encapsulated via the RFC 1042 (Standard for the Transmission of IP Datagrams over IEEE 802 Networks) encapsulation scheme • Maximum Data limited to 1500 octets • Transparent bridging to Ethernet WiFi Security

    14. Radio Frequency Spectrum 5.15-5.35 5.725-5.825GHz IEEE 802.11a HiperLAN/2 WiFi Security

    15. Channel Spacing (5MHz) 2.462 2.437 2.412 Non-overlapping channels WiFi Security

    16. Terminology: Access-Point (AP) • A transceiver that serves as the center point of a stand-alone wireless network or as the connection point between wireless and wired networks. • Device that contains IEEE 802.11 conformant MAC and PHY interface to the wireless medium, and provide access to a Distribution System for associated stations (i.e., AP is a STA) • Most often infra-structure products that connect to wired backbones • Implemented in a “box” containing a STA PC-Card. WiFi Security

    17. PC-Card Hardware Radio Hardware 802.11 frame format WMAC controller with Access Point Firmware (WNIC-AP) 802.3 frame format Bridge Software Driver Software (APDr) Ethernet V2.0 / 802.3 frame format Kernel Software (APK) Bridge Hardware Ethernet Interface Access-Point (AP) Architecture • Stations select an AP and “associate” with it • APs support • Roaming • Power Management • Time synchronization functions (Beaconing) • Traffic flows through AP WiFi Security

    18. Basic Configuration WiFi Security

    19. Terminology: Basic Service Set (BSS) • A set of stations controlled by a single “Coordination Function” (that determines when a station can transmit or receive) • Similar to a “cell” in pre IEEE terminology • A BSS may or may not have an AP WiFi Security

    20. Basic Service Set (BSS) BSS WiFi Security

    21. Terminology: Distribution System (DS) • A system to interconnect a set of BSSs • Integrated: A single AP in a standalone network • Wired: Using cable to interconnect the AP • Wireless: Using wireless to interconnect the AP WiFi Security

    22. Terminology: Independent Basic Service Set (IBSS) • A BSS forming a self-contained network in which no access to a Distribution System is available • A BSS without an AP • One of the stations in the IBSS can be configured to “initiate” the network and assume the Coordination Function • Diameter of the cell determined by coverage distance between two wireless stations WiFi Security

    23. Independent Basic Service Set (IBSS) IBSS WiFi Security

    24. Terminology: Extended Service Set (ESS) • A set of one or more BSS interconnected by a Distribution System (DS) • Traffic always flows via AP • Diameter of the cell is double the coverage distance between two wireless stations WiFi Security

    25. Terminology: Service Set Identifier (SSID) • Network name • Up to 32 bytes long • One network (ESS or IBSS) has one SSID • E.g., “WSU Wireless”; • Known Defaults for many vendors • “101” for 3COM • “tsunami” for Cisco WiFi Security

    26. Terminology: Basic Service Set Identifier (BSSID) • Cell identifier • One BSS has one BSSID • 6 bytes long • BSSID = MAC address of AP WiFi Security

    27. 802.11 Communication • CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) instead of Collision Detection • WLAN adapter cannot send and receive traffic at the same time on the same channel • Hidden Node Problem • Four-Way Handshake WiFi Security

    28. Four-Way Handshake Source Destination RTS – Request to Send CTS – Clear to Send DATA ACK WiFi Security

    29. Infrastructure operation modes Root Mode Repeater Mode WiFi Security

    30. 802.11 Packet Structure • 30 byte header • 4 addresses WiFi Security Graphic Source: Network Computing Magazine August 7, 2000

    31. 802.11 Physical Layer Packet Structure • 24 byte header (PLCP, Physical Layer Convergence Protocol) • Always transferred at 1 Mbps WiFi Security Graphic Source: Network Computing Magazine August 7, 2000

    32. 802.11 Frames • Format depends on type of frame • Control Frames • Management Frames • Data Frames WiFi Security

    33. 802.11 Frame Formats Bytes: 2 2 6 6 6 2 6 0-2312 4 Frame Frame Duration Sequence Body Addr 1 Addr 2 Addr 3 Addr 4 CRC Control ID Control 802.11 MAC Header Bits: 2 2 4 1 1 1 1 1 1 1 1 Protocol To From More Pwr More Type SubType Retry WEP Rsvd Version DS DS Frag Mgt Data Frame Control Field WiFi Security

    34. Bits: 2 2 4 1 1 1 1 1 1 1 1 Protocol To From More Pwr More Type SubType Retry WEP Rsvd Version DS DS Frag Mgt Data Frame Control Field To DS From DS Address 1 Address 2 Address 3 Address 4 0 0 DA SA BSSID N/A 0 1 DA BSSID SA N/A 1 0 BSSID SA DA N/A 1 1 RA TA DA SA Address Field Description Addr. 1 = All stations filter on this address. Addr. 2 = Transmitter Address (TA), Identifies transmitter to address the ACK frame to. Addr. 3 = Dependent on To and From DS bits. Addr. 4 = Only needed to identify the original source of WDS (Wireless Distribution System) frames. WiFi Security

    35. Bits: 2 2 4 1 1 1 1 1 1 1 1 Protocol To From More Pwr More Type SubType Retry WEP Rsvd Version DS DS Frag Mgt Data Frame Control Field Type field descriptions Type and subtype identify the function of the frame: • Type=00 Management Frame Beacon (Re)Association Probe (De)Authentication Power Management • Type=01 Control Frame RTS/CTS ACK • Type=10 Data Frame WiFi Security

    36. 802.11 Management Frames • Beacon • Timestamp, Beacon Interval, Capabilities, SSID, Supported Rates, parameters • Traffic Indication Map • Probe • SSID, Capabilities, Supported Rates • Probe Response • Timestamp, Beacon Interval, Capabilities, SSID, Supported Rates, parameters • Same for Beacon except for TIM WiFi Security

    37. Management Frames (cont’d) • Association Request • Capability, Listen Interval, SSID, Supported Rates • Association Response • Capability, Status Code, Station ID, Supported Rates • Re-association Request • Capability, Listen Interval, SSID, Supported Rates, Current AP Address • Re-association Response • Capability, Status Code, Station ID, Supported Rates WiFi Security

    38. Management Frames (cont’d) • Dis-association • Reason code • Authentication • Algorithm, Sequence, Status, Challenge Text • De-authentication • Reason WiFi Security

    39. Association + Authentication State 1: Unauthenticated Unassociated Successful authentication Deauthentication Deauthentication State 2: Authenticated Unassociated Successful association Disassociation State 3: Authenticated Associated WiFi Security

    40. Authentication • To control access to the infrastructure via authentication. • The station first needs to be authenticated by the AP in order to join the APs network. • Stations identify themselves to other stations (or APs) prior to data traffic or association. • Two authentication subtypes: • Open system. • shared key. WiFi Security

    41. Open System Authentication • A sends an authentication request to B • B sends the result back to A WiFi Security

    42. Shared Key Authentication WiFi Security

    43. Beacons sent out 10x second Advertise capabilities Station queries access points Requests features Access points respond With supported features Authentication just a formality May involve more frames Probe request Authentication request Association request Probe response Authentication response Association response Access Point Discovery WiFi Security

    44. Association • Next Step after authentication • Association enables data transfer between Client and AP • The Client sends an association request frame to the AP who replies to the client with an association response frame either allowing or disallowing the association WiFi Security

    45. Association • To establish relationship with AP • Stations scan frequency band to and select AP with best communications quality • Active Scan: send a “Probe request” on specific channels and assess response • Passive Scan: assess communications quality from beacon message • AP maintains list of associated stations in MAC FW • Record station capability (data-rate) • To allow inter-BSS relay • Station’s MAC address is also maintained in bridge learn table associated with the port it is located on WiFi Security

    46. WEP: Wired Equivalent Privacy • Designed to be computationally efficient, self-synchronizing, and exportable • Data headers remain unencrypted. • The cipher used is RC4(v, k) • Shared key k: Manual distribution among clients. WiFi Security

    47. WEP Encryption • WEP encryption key: a shared 40- or 104-bit long number. • WEP keys are used for authentication and encryption of data. • A 32-bit integrity check value (ICV) is calculated that provides data integrity for the MAC frame. The ICV is appended to the end of the frame data. • A 24-bit initialization vector (IV) is appended to the WEP key. • IV and WEP encryption key are input to a pseudo-random number generator (PRNG) to generate a bit sequence that is the same size as the combination of [data+ICV]. • The PRNG bit sequence is bit-wise XORed with [data+ICV] to produce the encrypted portion of the payload that is sent between the wireless AP and the wireless client. • The IV is added to the front of the encrypted [data+ICV] which becomes the payload for the wireless MAC frame. • The result is IV+ encrypted [data+ICV]. WiFi Security

    48. WEP Decryption • IV is obtained from the front of the MAC payload. • WEP encryption key is concatenated with the IV. • The concatenated WEP encryption key and IV is used as the input of the same PRNG to generate a bit sequence of the same size as the combination of the [data + ICV]. • The PRNG bit sequence is XORed with the encrypted [data+ICV] to decrypt the [data+ICV] portion of the payload. • The ICV for the data portion of the payload is calculated and compared with the value included in the incoming frame. • The WEP key remains constant over a long duration (days and months) but the IV can be changed frequently depending on the degree of security needed. WiFi Security

    49. 802.11 Hdr Data 802.11 Hdr 802.11 Hdr IV Append ICV = CRC32(Data) Check ICV = CRC32(Data) Select and insert IV Per-packet Key = IV || RC4 Base Key RC4 Encrypt Data || ICV Remove IV from packet Per-packet Key = IV || RC4 Base Key RC4 Decrypt Data || ICV ICV Data ICV Encrypted Data 24 bits WEP WiFi Security

    50. WEP Protocol • Key is shared by all clients and the base station. • PRNG – Pseudo Random Number Gen WiFi Security