Wi-Fi Technology

Agenda• Introduction• Wi-Fi Technologies• Wi-Fi Architecture• Wi-Fi Network Elements• How a Wi-Fi Network Works• Wi-Fi Network Topologies• Wi-Fi Configurations• Applications of Wi-Fi• Wi-Fi Security• Advantages/ Disadvantages of Wi-Fi

Introduction• Wireless Technology is an alternative to Wired

Technology, which is commonly used, for connecting devices in wireless mode.

• Wi-Fi (Wireless Fidelity) is a generic term that refers to the IEEE 802.11 communications standard for Wireless Local Area Networks (WLANs).

• Wi-Fi Network connect computers to each other, to the internet and to the wired network.

The Wi-Fi Technology

Wi-Fi Networks use Radio Technologies to transmit & receive data at high speed:

• IEEE 802.11b• IEEE 802.11a• IEEE 802.11g

IEEE 802.11b

• Appear in late 1999• Operates at 2.4GHz radio spectrum• 11 Mbps (theoretical speed) - within 30 m Range• 4-6 Mbps (actual speed)• 100 -150 feet range• Most popular, Least Expensive• Interference from mobile phones and Bluetooth

devices which can reduce the transmission speed.

IEEE 802.11a

• Introduced in 2001• Operates at 5 GHz (less popular) • 54 Mbps (theoretical speed)• 15-20 Mbps (Actual speed)• 50-75 feet range• More expensive• Not compatible with 802.11b

IEEE 802.11g

• Introduced in 2003• Combine the feature of both standards (a,b)• 100-150 feet range• 54 Mbps Speed• 2.4 GHz radio frequencies• Compatible with ‘b’

802.11 Physical Layer

There are three sublayers in physical layer:

• Direct Sequence Spread Spectrum (DSSS)• Frequency Hoping Spread Spectrum (FHSS)• Diffused Infrared (DFIR) - Wide angle

DSSS• Direct sequence signaling technique divides the 2.4 GHz band into 11 22-

MHz channels. Adjacent channels overlap one another partially, with three of the 11 being completely non-overlapping. Data is sent across one of these 22 MHz channels without hopping to other channels.

IEEE 802.11 Data Link Layer

The data link layer consists of two sublayers :

• Logical Link Control (LLC) • Media Access Control (MAC).

802.11 uses the same 802.2 LLC and 48-bit addressing as other 802 LANs, allowing for very simple bridging from wireless to IEEE wired networks, but the MAC is unique to WLANs.

802.11 Media Access Control• Carrier Sense Medium Access with collision

avoidance protocol (CSMA/CA)• Listen before talking• Avoid collision by explicit Acknowledgement (ACK)• Problem: additional overhead of ACK packets, so slow

performance • Request to Send/Clear to Send (RTS/CTS)

protocol• Solution for “hidden node” problem• Problem: Adds additional overhead by temporarily

reserving the medium, so used for large size packets only retransmission would be expensive

802.11 Media Access Control(cont.)

• Power Management• MAC supports power conservation to extend the battery life of

portable devices• Power utilization modes

• Continuous Aware Mode• Radio is always on and drawing power

• Power Save Polling Mode• Radio is “dozing” with access point queuing any data for it• The client radio will wake up periodically in time to receive regular beacon signals from the access point.

• The beacon includes information regarding which stations have traffic waiting for them

• The client awake on beacon notification and receive its data

802.11 Media Access Control(cont.)

• Fragmentation• CRC checksum

• Each pkt has a CRC checksum calculated and attached to ensure that the data was not corrupted in transit

• Association & Roaming

Elements of a WI-FI Network

• Access Point (AP) - The AP is a wireless LAN transceiver or “base station” that can connect one or many wireless devices simultaneously to the Internet.

• Wi-Fi cards - They accept the wireless signal and relay information.They can be internal and external.(e.g PCMCIA Card for Laptop and PCI Card for Desktop PC)

• Safeguards - Firewalls and anti-virus software protect networks from uninvited users and keep information secure.

How a Wi-Fi Network Works• Basic concept is same as Walkie talkies.• A Wi-Fi hotspot is created by installing an access point to an

internet connection.• An access point acts as a base station. • When Wi-Fi enabled device encounters a hotspot the device

can then connect to that network wirelessly.• A single access point can support up to 30 users and can

function within a range of 100 – 150 feet indoors and up to 300 feet outdoors.

• Many access points can be connected to each other via Ethernet cables to create a single large network.

Wi-Fi Network Topologies

• AP-based topology (Infrastructure Mode)

• Peer-to-peer topology (Ad-hoc Mode)

• Point-to-multipoint bridge topology

AP-based topology• The client communicate through Access Point. • BSA-RF coverage provided by an AP.• ESA-It consists of 2 or more BSA.• ESA cell includes 10-15% overlap to allow roaming.

Peer-to-peer topology• AP is not required.• Client devices within a

cell can communicate directly with each other.

• It is useful for setting up of a wireless network quickly and easily.

Point-to-multipoint bridge topologyThis is used to connect a LAN in one building to a LANs in other buildings even if the buildings are miles apart.These conditions receive a clear line of sight between buildings. The line-of-sight range varies based on the type of wireless bridge and antenna used as well as the environmental conditions.

Wi-Fi Configurations

Wi-Fi Configurations

Wi-Fi Configurations

Wi-Fi Applications

• Home• Small Businesses or SOHO• Large Corporations & Campuses• Health Care• Wireless ISP (WISP)• Travellers

Wi-Fi Security Threats

• Wireless technology doesn’t remove any old security issues, but introduces new ones• Eavesdropping• Man-in-the-middle attacks• Denial of Service

Eavesdropping

• Easy to perform, almost impossible to detect• By default, everything is transmitted in clear text

• Usernames, passwords, content ...• No security offered by the transmission medium

• Different tools available on the internet• Network sniffers, protocol analysers . . .• Password collectors

• With the right equipment, it’s possible to eavesdrop traffic from few kilometers away

MITM Attack1. Attacker spoofes a

disassociate message from the victim

2. The victim starts to look for a new access point, and the attacker advertises his own AP on a different channel, using the real AP’s MAC address

3. The attacker connects to the real AP using victim’s MAC address

Denial of Service• Attack on transmission frequecy used

• Frequency jamming• Not very technical, but works

• Attack on MAC layer• Spoofed deauthentication / disassociation messages• can target one specific user

• Attacks on higher layer protocol (TCP/IP protocol)• SYN Flooding

Wi-Fi Security

The requirements for Wi-Fi network security can be broken down into two primary components:

• Authentication User Authentication Server Authentication

• Privacy

Authentication

• Keeping unauthorized users off the network• User Authentication

• Authentication Server is used• Username and password • Risk:

• Data (username & password) send before secure channel established

• Prone to passive eavesdropping by attacker• Solution

• Establishing a encrypted channel before sending username and password

Authentication (cont..)

• Server Authentication• Digital Certificate is used• Validation of digital certificate occurs

automatically within client software

Wi-Fi Security Techniques• Service Set Identifier (SSID)

• Wired Equivalent Privacy (WEP)

• 802.1X Access Control

• Wireless Protected Access (WPA)

• IEEE 802.11i

Service Set Identifier (SSID)

• SSID is used to identify an 802.11 network• It can be pre-configured or advertised in

beacon broadcast• It is transmitted in clear text

• Provide very little security

Wired Equivalent Privacy (WEP)• Provide same level of security as by wired network• Original security solution offered by the IEEE 802.11 standard• Uses RC4 encryption with pre-shared keys and 24 bit

initialization vectors (IV)• key schedule is generated by concatenating the shared secret

key with a random generated 24-bit IV• 32 bit ICV (Integrity check value)• No. of bits in keyschedule is equal to sum of length of the

plaintext and ICV

Wired Equivalent Privacy (WEP) (cont.)

• 64 bit preshared key-WEP• 128 bit preshared key-WEP2• Encrypt data only between 802.11 stations.once it enters the

wired side of the network (between access point) WEP is no longer valid

• Security Issue with WEP• Short IV• Static key

• Offers very little security at all

802.1x Access Control• Designed as a general purpose network access control mechanism

• Not Wi-Fi specific• Authenticate each client connected to AP (for WLAN) or switch port (for

Ethernet) • Authentication is done with the RADIUS server, which ”tells” the access

point whether access to controlled ports should be allowed or not• AP forces the user into an unauthorized state • user send an EAP start message• AP return an EAP message requesting the user’s identity• Identity send by user is then forwared to the authentication server by AP• Authentication server authenticate user and return an accept or reject

message back to the AP• If accept message is return, the AP changes the client’s state to authorized

and normal traffic flows

802.1x Access Control

Wireless Protected Access (WPA)

• WPA is a specification of standard based, interoperable security enhancements that strongly increase the level of data protection and access control for existing and future wireless LAN system.

• User Authentication• 802.1x • EAP

• TKIP (Temporal Key Integrity Protocol) encryption• RC4, dynamic encryption keys (session based)

• 48 bit IV• per packet key mixing function

• Fixes all issues found from WEP• Uses Message Integrity Code (MIC) Michael

• Ensures data integrity• Old hardware should be upgradeable to WPA

Wireless Protected Access (WPA)(cont.)

• WPA comes in two flavors• WPA-PSK

• use pre-shared key• For SOHO environments• Single master key used for all users

• WPA Enterprise• For large organisation• Most secure method• Unique keys for each user• Separate username & password for each user

WPA and Security Threats

• Data is encrypted• Protection against eavesdropping and man-in-the-

middle attacks

• Denial of Service• Attack based on fake massages can not be used.• As a security precaution, if WPA equipment sees two

packets with invalid MICs within a second, it disassociates all its clients, and stops all activity for a minute

• Only two packets a minute enough to completely stop a wireless network

802.11i

• Provides standard for WLAN security• Authentication

• 802.1x• Data encryption

• AES protocol is used• Secure fast handoff-This allow roaming

between APs without requiring client to fully reauthenticate to every AP.

• Will require new hardware

Advantages• Mobility• Ease of Installation• Flexibility• Cost• Reliability• Security• Use unlicensed part of the radio spectrum• Roaming• Speed

Limitations

• Interference• Degradation in performance• High power consumption• Limited range