Lecture 8 of IT security course is about Wireless LAN. Lecture start with En.Mohd Zaki briefly explained on what is wireless LANs. After listened to En.Mohd Zaki, I know that a wireless LAN or WLAN allows user connect to a local area network through a wireless connection. The IEEE 802.11 group of standards specifies the technologies for wireless LANs. 802.11 focuses on layer 1 and layer 2 of OSI layer which are physical layer and data link layer.
802.11 components defined two pieces of equipment which include wireless station and access point. Wireless station is a desktop or laptop PC or PDA with a wireless NIC. Access point is a bridge between wireless and wired networks and composed of radio, wired network interface and bridging software. 802.11 modes include infrastructure mode and ad hoc mode.
Infrastructure mode is Wireless network consists of at least one access point (AP) connected to the wired network infrastructure and a set of wireless end stations. An access point controls encryption on the network and may bridge or route the wireless traffic to a wired Ethernet network (or the Internet). Access points that act as routers can also assign an IP address to PC's using DHCP services. AP's can be compared with a base station used in cellular networks. This configuration is called a Basic Service Set (BSS). An Extended Service Set (ESS) consists of two or more BSSs forming a single sub network. Ad hoc mode is An Extended Service Set (ESS) consists of two or more BSSs forming a single sub network. Ad-Hoc mode is a set of 802.11 wireless stations that communicate directly with each other without using an access point or any connection to a wired network. This basic topology is useful in order to quickly and easily set up a wireless network anywhere. Ad-Hoc Mode is also called peer-to-peer mode or an Independent Basic Service Set (IBSS).
Besides, En. Mohd Zaki also explained about RTS/CTS. Request to Send (RTS) frame is sent by a potential transmitter to the receiver and a Clear to Send (CTS) frame is sent from the receiver in response to the received RTS frame. All other stations hear this and delay any transmission. If the CTS frame is not received within a certain time interval, RTS frame is retransmitted by executing a backoff algorithm. 
Follow by, En.Mohd Zaki explained WLAN standards which includes to us. The differences are:
| 802.11a | With data transfer rates up to 54Mbps, it is faster than 802.11b and can support more simultaneous connections. Because it operates in a more regulated frequency, it gets less signal interference from other devices and is considered to be better at maintaining connections. In areas with major radio interference (e.g., airports, business call centers), 802.11a will outperform 802.11b. It has the shortest range of the three standards (generally around 60 to 100 feet), broadcasts in the 5GHz frequency, and is less able to penetrate physical barriers, such as walls. |
| 802.11b | It supports data transfer speeds up to 11Mbps. It's better than 802.11a at penetrating physical barriers, but doesn't support as many simultaneous connections. It has better range than 802.11a (up to 300 feet in ideal circumstances). It's more susceptible to interference, because it operates on the same frequency (2.4GHz) as many cordless phones and other appliances. Therefore, it's not considered a good technology for applications that require absolutely reliable connections, such as live video streaming. |
| 802.11g | It's faster than 802.11b, supporting data transfer rates up to 54Mbps. It has a slightly shorter range than 802.11b, but still better than 802.11a. It is backward-compatible with 802.11b products, but will run only at 802.11b speeds when operating with them. It uses the 2.4GHz frequency, so it has the same problems with interference as 802.11b. |
There are three basic security services defined by IEEE for the WLAN environment such as authentication, integrity, and confidentiality. Authentication provides a security services to verify the identity of communicating parties, integrity to ensure message are not modified and confidentiality to provide privacy achieved by a wired network. WEP is the encryption algorithm built into 802.11 standards. WEP (Wired Equivalent Privacy) encryption uses RC4 stream cipher with 40 or 104 bit keys and a 24 bit initialization vector. Most 802.11 devices allow WEP keys to be entered using an ASCII passphrase or in hexadecimal format. The conversion between these two formats is an industry standard which is shared by almost all vendors of 802.11 equipment. There are two WEP security tools describes by En.Mohd Zaki which are AirSnort and WEPCrack. AirSnort is a WLAN tool which crack encryption keys on 802.11 WEP network. AirSnort operates by passively monitoring transmissions and computing the WEP encryption key when enough packets have been gathered. WEP Crack is a tool that cracks 802.11 WEP encryption keys by exploiting the weaknesses of RC4 key scheduling.
At the end of the lecture, En. Mohd Zaki told us that he will show us how to hack wireless network at lab section.
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