B030710154

Wireless Security

Wireless LAN is a connection to network without using a cable. Connection in wireless LAN usually at 1Mbps and 2 Mbps. Wireless LAN use radio frequency to transmit the data, and it can go through the building. Signals of wireless LAN weakened by wall, floor and interference. Wireless LAN 802.11 focus on physical layer and data link layer.

802.11 Physical layer

• Originally three alternative physical layers

o Two incompatible spread-spectrum radio in 2.4Ghz ISM band

§ Frequency Hopping Spread Spectrum (FHSS)

· 75 channels

§ Direct Sequence Spread Spectrum (DSSS)

· 14 channels (11 channels in US)

• One diffuse infrared layer
• 802.11 speed

o 1 Mbps or 2 Mbps

802.11 Data link layer

• — Layer 2 split into:

o Logical Link Control (LLC).

o Media Access Control (MAC).

• — LLC - same 48-bit addresses as 802.3.
• — 802.11 always slower than equivalent 802.
• — MAC - CSMA/CD not possible.

o Can’t listen for collision while transmitting.

• — CSMA/CA – Collision Avoidance.

o Sender waits for clear air, waits random time, then sends data.

o Receiver sends explicit ACK when data arrives intact.

o Also handles interference.

o But adds overhead.

Wireless 802.11 has two modes, instructure and ad-hoc mode. Instructure mode can have one access point or basic service set(BSS) and also can have two or more BSS perform as single subnet, most corporate LAN use in this mode. Ad-hoc or peer to peer is useful for easy and quick wireless network.

802.11 can be divided into:

1. 802.11a

• — 802.11a ratified in 2001
• — Supports up to 54Mbps in 5 Ghz range.

o Higher frequency limits the range

o Regulated frequency reduces interference from other devices

• — 12 non-overlapping channels
• — Usable range of 30 metres
• — Average throughput of 30 Mbps
• — Not backwards compatible

2. 802.11g

• — 802.11g ratified in 2002
• — Supports up to 54Mbps in 2.4Ghz range.

o Backwards compatible with 802.11b

• — 3 non-overlapping channels
• — Range similar to 802.11b
• — Average throughput of 30 Mbps
• — 802.11n due for November 2006

o Aiming for maximum 200Mbps with average 100Mbps

Three basic security services defined by IEEE for the WLAN environment

o Authentication

§ provide a security service to verify the identity of communicating client stations

o Integrity

§ to ensure that messages are not modified in transit between the wireless clients and the access point in an active attack

o Confidentiality

§ to provide “privacy achieved by a wired network”