Wireless LAN Security
The list of advantages for implementing a wireless LAN (WLAN) is impressive. WLANs provide true mobility for users and do not force them to be restricted to their desk in order to access network resources. Not only does this provide greater flexibility, but it can also result in substantially increased productivity by employees. Another advantage of wireless technology is installation. No longer are cable drops required for each computer on the network—a single connection to an access point is all that is needed. This both decreases installation costs and allows for wireless networks to be installed in locations where previously it would have been difficult or impossible to install wiring, such as in older buildings or large warehouses.
Despite these and many other advantages to wireless networking, one single disadvantage has proven to be a major stumbling block to the adoption of wireless technology. In fact, many organizations and individuals have resisted all efforts to installing a WLAN because of it. What is this critical element that has had such a dramatic impact on wireless LAN implementation? In a word, security.
When compared to wired networks, wireless LANs have several unique features that make them more vulnerable to attacks. Coupled with the fact that wireless security in the original IEEE 802.11 standard was not properly implemented and thus further exposes wireless networks to a variety of attacks, security has been the Achilles heel of wireless networking for many years. However, much of that is now starting to change. By implementing new wireless security technologies wireless LANs can, according to many wireless experts, be made as secure as their wired counterparts.
IEEE 802.11 Security Vulnerabilities
In September of 1999 the IEEE committee ratified the 802.11b and 802.11a WLAN standard, which included Wired Equivalent Privacy (WEP) technology for authentication and packet encryption. By early 2001, independent studies from universities and commercial institutions had identified weaknesses in WEP. These weaknesses revealed that even with WEP enabled, an attacker with the proper tools and a moderate amount of technical knowledge could gain unauthorized access to a WLAN. Because WEP is used for both encryption and authentication, its weaknesses were particularly alarming. In addition, other vulnerabilities in related 802.11 wireless security implementations were also revealed, which resulted in a general distrust of wireless security.
WEP is used in IEEE 802.11 to encrypt wireless transmissions. Unlike a wired LAN that requires access to the cable plant in order to view data that is being transmitted, data transmitted by a wireless LAN “in the air” could be intercepted and viewed by an attacker.
WEP relies on a secret key that is “shared” between a wireless device and the access point. That is, the same key must be installed on both the device and the access point. WEP keys must be a minimum of 64 bits in length. Most vendors add an option to use a larger 128-bit WEP key for added security, because a longer key may be more difficult to break. Keys may be created in several different ways, depending on the vendor implementation. The different options for creating WEP keys range from the user creating a 64-bit WEP key by entering five ASCII characters (for example 5y7js), to creating 128-bit WEP key by entering 16 hexadecimal characters (for example 0x3344556677889900ABCDEFGHIJ).
The WEP default key used for encryption is combined with an initialization vector (IV). The IV is a 24-bit value that changes each time a packet is encrypted. This random IV value helps ensure that another random number needed in the encryption process can be created. If only the default key were used to create a random number, then the number generated could be the same each time. Varying the IV each time ensures that the random number it creates is indeed random. In this sense the IV (along with the default key) is used as a “seed” for generating a random number. To encrypt packets WEP uses a 64-bit or 128-bit number, which is made up of a 24-bit initialization vector (IV) and a 40-bit or 104-bit secret key.
However, WEP implementation violates the cardinal rule of cryptography. A mathematical key that creates a detectable pattern or structure provides an attacker with valuable information to break the encryption (keys that create this type of repeating pattern are known as weak keys). The implementation of WEP creates a detectable pattern for attackers. IVs are 24-bit numbers, meaning there are 16,777,216 possible values. An AP transmitting at only 11 Mbps can send and receive 700 packets each second. If a different IV were used for each packet, then the IVs would start repeating in fewer than seven hours (a “busy” AP can produce duplicates in fewer than five hours). An attacker who captures packets for this length of time can see the duplication and use it to crack the code.
Yet it does not always require seven hours of capturing packets to see the IV repeat. Some wireless systems always start with the same IV after the system is restarted and then follow the same sequence of incrementing IVs. If 50 devices start in the morning they may all be given the same initial IV and then follow the same sequence of subsequent IVs. This would give an attacker the same IV value that would appear 50 times for each value in the sequence, which would be sufficient data for cracking the code. Because of the weaknesses of the implementation of WEP, it is possible for an attacker to identify two packets derived from the same IV (called a collision). Once the attacker has that information, he or she can begin a key stream attack, which is a method of determining the key stream by analyzing two packets that were created from the same IV. The attacker can then derive the plaintext of any packet that uses that IV.
Wireless Security Models
Due to the weaknesses in WEP, alternative wireless security implementations were designed. These implementations used other technologies in order to make WLANs secure. It is now generally recognized that there are three security models that can provide a higher degree of wireless security. These models are the Transitional Model, the Personal Model, and the Enterprise Model.
Transitional Security Model
Someone once said security is like car insurance: you realize you should have had more only after it’s too late! It is important to implement the most comprehensive security model possible in order to protect information. Failing to adequately protect information from all potential attacks can result in only partial coverage and will give rise to serious consequences.
With that being said, however, there are occasions when the best security model cannot be implemented. For example, a public library may have installed an 802.11b network several years ago for its patrons but due to funding cannot now afford to purchase new equipment that supports higher levels of security. Or, a business may be deeply involved in another project and cannot afford the time to update the wireless LAN to new equipment that supports IEEE 802.11i. What should be done in these instances?
The answer may be to implement the highest level of security based upon the current equipment in use. Although this is not the optimal solution, it is better than doing nothing at all. It should, however, be recognized that this should only be considered a transitional phase until a migration to stronger wireless security is possible. Sometimes called the Transitional Security Model, this should only be implemented as a temporary solution. This model should be considered as the absolute minimum level of security for a home or an apartment that uses a WLAN. Table 1 lists the features of the Transitional Security Model.
| Category | Security mechanism | Security level |
| Authentication | Shared key authentication | Low |
| Authentication | SSID beaconing | Low |
| Authentication | MAC address filtering | Low |
| Encryption | WEP | Low |
Personal Security Model
A dramatically increased level of security can be achieved through use of the Personal Security Model. The Personal Security Model is designed for single users or small office home office (SOHO) settings of generally ten or fewer wireless devices. The Personal Security Model is intended for settings in which an authentication server is unavailable. If an authentication server is available, the Enterprise Security Model should be used instead.
The Personal Security Model is divided into two sections: WPA and WPA2. Older equipment may be forced to implement WPA, while newer APs and wireless NICs can support WPA2. It is important the highest level of security be implemented within the model: if the equipment can support WPA2, then that should be used instead of WPA. Table 2 outlines the Personal Security Model.
| Security Model | Category | Security mechanism | Security level |
| WPA Personal Security | Authentication | PSK | Medium |
| WPA Personal Security | Encryption | TKIP | Medium |
| WPA2 Personal Security | Authentication | PSK | Medium |
| WPA2 Personal Security | Encryption | AES-CCMP | High |
Enterprise Security Model
The most secure level of security for Wireless LANs that can be achieved today is the Enterprise Security Model. The Enterprise Security Model is designed for medium to large-size organizations such as businesses, government agencies, and universities. The Enterprise Security Model is intended for settings in which an authentication server is available. (If an authentication server is not available, the highest level of the Personal Security Model should be used instead.)
The Enterprise Security Model is divided into two sections, WPA and WPA2. Older equipment may be forced to implement WPA, while newer AP’s and wireless NIC’s can support WPA2. In addition, there are other types of security tools that can be used to help protect the network. The features of the Enterprise Security Model are outlined in Table 3.
| Security Model | Category | Security mechanism | Security level |
| WPA Enterprise Security | Authentication | 802.1x | High |
| WPA Enterprise Security | Encryption | TKIP | Medium |
| WPA2 Enterprise Security | Authentication | 802.1x | High |
| WPA2 Enterprise Security | Encryption | AES-CCMP | High |
Although the original security implementation of the IEEE 802.11 standard contained several vulnerabilities, most security experts agree that these vulnerabilities have been addressed with new and improved technologies. Today’s wireless LANs should be designed with the highest possible level of security for that setting in order to ensure the security of the information on the network.
>>>Mark Ciampa