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How Spread Spectrum Works
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Imagine you and a friend are standing on opposite ends of a noisy room You want to say something private to your friend, but he can t hear you over the ambient noise and neither of you can move across the room The high power solution is to write the message in large letters and hold the sign over your head Unfortunately, this is not very private A reduced power solution would be to write the message on a piece of paper and ask somebody to deliver it to your friend The problem is, that person will see the message and/or he or she may forget to give it to your friend A better option is to write each word on five pieces of paper Hand the first word to five random people wandering through the room and ask them to deliver it to your friend Now do the same for the second word, and so on Chances are, at least one copy of each word will get through to your friend Furthermore, nobody else in the room will have the complete message You used the same amount of reduced power to send the message, but with more security and reliability This is the basic concept behind spread spectrum technology Two types of spread spectrum systems are in use: Frequency Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Spectrum (DSSS) FHSS: A wide frequency band is divided into a number of smaller bands The transmitter and receiver initially start communicating over one of these smaller bands At specific intervals, the transmitter and receiver both change to a new band, selected by using a pre-arranged system DSSS: A wide frequency band is divided into a few narrower bands Each device uses one of the narrower bands The device then transmits data over multiple frequencies within this band simultaneously Wi-Fi uses DSSS because of the higher data rate it can achieve
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How Wireless Integrates into Your Network
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There are three types of wireless network components: access points, end points, and bridges An access point connects a wired network to a wireless network It s a device that broadcasts the network signal to the surrounding environment End points are the wireless adapters that are found in PCs and laptops These are just like traditional Ethernet adapters, except they have antennas instead of jacks for an Ethernet cable Bridges are used to extend the range of a wireless network They receive signals from a nearby access point or bridge and rebroadcast them (see Figure 16-2)
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194 Network Security Illustrated
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In this network, a wireless access point provides connectivity to users throughout the building A bridge boosts the signal upstairs Two users are creating a peer to peer network between their two laptops, and a curious snooper outside is trying to latch onto the network
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Access Point
Wired Workstations WarChalking
Adhoc Wireless
Concept by
(wwwsagesecurecom) | 2003 XPLANEcom
I Figure 16-2
When a wireless end point is within range of an access point, it will attempt to connect to the access point Most wireless connections support some type of encryption and/or authentication system In many cases, possession of a valid encryption key is the only form of authentication necessary Some access points support additional types of authentication for added security It s also possible for two or more wireless end points to create a peer-to-peer network without an access point This is called an ad hoc wireless network
Security Considerations
Wi-Fi networking technology is pretty simple and easy to use It takes little effort or understanding to add wireless connectivity to a network in an insecure manner It takes a significant amount of knowledge and effort to add Wi-Fi support in a way that doesn t significantly reduce overall network security Unfortunately, the ease of Wi-Fi means that people who don t understand the security issues can still successfully create such networks by installing a Wi-Fi device onto the network Let s look at some of the reasons why Wi-Fi can be more trouble than it s worth: Range: The biggest problem with wireless communications is that the data ultimately travels everywhere Even though the box says that your wireless LAN card
Part VI Connecting Networks 195 has a 100-meter range, a properly connected tin can will boost the range to a kilometer! The reason for this is that the LAN signal is still traveling well past the 100- 16 meter range; it s just much weaker The can acts as an antenna, increasing your LAN Connecting Networks: card s sensitivity and enabling it to pick up the weaker signals Wireless With the right tools, even extremely short-range signals can be seen from a dis- Connections tance That s the theory behind TEMPEST, a technology that can show someone what s on your computer monitor from across the street It works by using an incredibly sensitive antenna to detect the electrical radiation coming from your video card Sci-fi Hardly Signals get weak, but they keep going until interference distorts the signal beyond comprehension The signals from the first radio broadcast ever are still traveling through the universe and have already reached star systems roughly 100 light-years away In fact, the SETI program is relying on this very fact to detect other life in the universe They hope to eventually detect faint radio signals generated by other civilizations If ET can eavesdrop on your data, what chance do you have to protect it against the average hacker who s much closer and much more likely to be listening Interference: The other evil side effect of the range problem is interference Two signals broadcasting at the same frequency will distort each other As a result, pandemonium can occur when multiple radio devices are broadcasting near each other at similar frequencies The problem is that many wireless technologies use similar frequencies For example, Bluetooth, Wi-Fi and newer cordless phones all operate at the 24 GHz range of frequencies When these devices are close enough to one another they can create interference issues Unfortunately, the likelihood of unavoidable proximity problems is high, because these devices are becoming fairly ubiquitous within the home and office environments Even unrelated systems can cause interference Microwave ovens, some types of lights, and various kinds of machinery can leak radiation in the 24 GHz range, causing interference There are a number of technological solutions for mitigating interference, including: use of different frequencies, use of spread spectrum technology, and intelligent avoidance algorithms Newer Wi-Fi technology is capable of operating in the 5 GHz range, which will help to avoid interference with other 24 GHz devices (until more devices move to 5 GHz) Bluetooth uses spread spectrum to minimize interference among other Bluetooth devices, but as the signal hops around it will hop in and out of bands used by Wi-Fi networks As a result, a Bluetooth device may cause a nearby Wi-Fi network connection to perform badly or completely fail Newer Bluetooth and Wi-Fi systems are being designed with intelligent broadcasting systems for avoiding interference These system monitor interference levels and adjust the way in which data is transmitted to minimize conflicts The problem is that intelligent algorithms make already complex systems even more complex Protocol weaknesses: Both Bluetooth and Wi-Fi technologies have flawed underlying security models Bluetooth security relies upon its short range, spread spectrum signal hopping, and encryption As we ve discussed, range can be boosted with the right equipment Similarly, it s not too difficult to reassemble a spread spectrum
196 Network Security Illustrated signal, especially if intelligent algorithms limit the valid spectrum channels due to interference on other channels Finally, the encryption system is initialized with a personal identification number (PIN) code that is often set to 0000 , making it trivial for hackers to forge a connection Wi-Fi also has serious security problems Its encryption system, known as Wireless Encryption Protocol (WEP), is relatively easy to crack within a short period of time due to inherent flaws in the protocol design To make matters worse, most consumer-grade Wi-Fi products initially have encryption turned off As a result, the vast majority of Wi-Fi access points offer full, public access to anyone within range (1000 meters with an antenna) of the network This gets to be particularly problematic when an employee sets up a Wi-Fi access point on the office network Suddenly, your nicely secured internal LAN has a giant hole offering hackers carte blanche access to your entire network and its bandwidth Exposure: Just because you can t see them, doesn t mean they can t see you When you activate a wireless connection with another machine, hackers can see both machines Even though you re not technically on the hacker s LAN, there s nothing to stop him or her from broadcasting signals at your computer He or she may even be able to establish an ad hoc wireless network connection with your system without your knowledge Even if you think you re protected from unauthorized connections, remember that a software bug on your system could let the hacker in through a back door while you re busy having what you think is a secure conversation through your virtual private network (VPN) Unsafe wireless: The availability of free Wi-Fi in metropolitan areas makes it really tempting to hop on But how safe are these LANs If a hacker gets into your system when you re on a public Wi-Fi LAN he can control your system when it s back at your office network Using a free Wi-Fi LAN is like having casual sex without a condom (assuming like is used in the broadest sense possible)
What people think: Wireless connectivity is a very advanced concept It is difficult to imagine that hackers can grab data out of thin air What we think: Wireless connectivity is here to stay, but has major security issues that need to be addressed immediately Current use of wireless networks is extremely risky
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