Although security was originally included with 802.11 standards, it soon became obvious that it wasn't enough. Wireless securityor the lack of ithas been a major contributor to IT managers' reluctance to adapt wireless LANs. Recently, wireless security has improved dramatically, providing IT managers with an acceptable level of comfort to proceed with the installation of WLANs. IEEE 802.11i, released in June 2004, addresses current security concerns. In addition to the 802.11 suite of standards, the 802.1x standard can be used for wireless security. More precisely, 802.1x addresses port-based access control. Wireless Security IssuesA main issue with wireless communication is unauthorized access to network traffic or, more precisely, the watching, displaying, and logging of network traffic, also known as sniffing. Contrary to a wired network, where a hacker would need to be physically located at the corporate premises to gain access through a network drop, with a wireless network, the intruder can access the network from a location outside the corporate building. WLANs use radio frequencies, and their signals propagate through ceilings and walls. Therefore, wireless eavesdropping, known as war driving or walk-by hacking, and rogue WAPsunauthorized WAPs that allow a hacker access to a networkare two significant security issues with wireless networks. Moreover, wireless equipment tends to ship with open access. Not only is traffic propagated in clear text, but WAPs also voluntarily broadcast their identity, known as Service Set Identifiers (SSIDs). Wireless Threat MitigationThanks to the wireless open-access default mode, we can join a wireless network from our favorite coffee shop or hotel room; however, this unrestricted access is not advisable for corporate networks. Wireless network security can be classified into the following three categories:
Basic Wireless SecurityBasic wireless security is provided by the following built-in functions:
SSIDsAn SSID is a code that identifies membership with a WAP. All wireless devices that want to communicate on a network must have their SSID set to the same value as the WAP SSID to establish connectivity with the WAP. By default, a WAP broadcasts its SSID every few seconds. This broadcast can be stopped so that a drive-by hacker can't automatically discover the SSID and hence the WAP. However, because the SSID is included in the beacon of every wireless frame, it is easy for a hacker equipped with sniffing equipment to discover the value and fraudulently join the network.
Being able to join a wireless network by the mere fact of knowing the SSID is referred to as open authentication. Wired Equivalent PrivacyWEP can be used to alleviate the problem of SSID broadcasts by encrypting the traffic between the wireless clients and WAPs. Joining a wireless network using WEP is referred to as shared-key authentication, where the WAP sends a challenge to the wireless client who must return it encrypted. If the WAP can decipher the client's response, the WAP has the proof that the client possesses valid keys and therefore has the right to join the wireless network. WEP comes in two encryption strengths: 64-bit and 128-bit. Note Even if a user manages to proceed with open authenticationfor example, he guesses the SSIDif WEP is activated, he could not communicate with the WAP until he obtains the keys. However, WEP is not considered secure: A hacker sniffing first the challenge and then the encrypted response could reverse-engineer the process and deduce the keys used by the client and WAP. MAC Address VerificationTo further wireless security, a network administrator could use MAC address filtering, in which the WAP is configured with the MAC addresses of the wireless clients that are to be permitted access. Unfortunately, this method is also not secure because frames could be sniffed to discover a valid MAC address, which the hacker could then spoof. Enhanced Wireless SecurityStronger security standards, shown in Table 5-2, were created to replace the weaknesses in WEP.
802.1xIEEE 802.1x is a port-based network access control standard. It provides per-user, per-session, mutual strong authentication, not only for wireless networks but also for wired networks, if need be. Depending on the authentication method used, 802.1x can also provide encryption. Based on the IEEE Extensible Authorization Protocol (EAP), 802.1x allows WAPs and clients to share and exchange WEP encryption keys automatically. The access point acts as a proxy, doing the heavier computational load of encryption. The 802.1x standard also supports a centralized key management for WLANs. Wi-Fi Protected AccessWPA was introduced as an intermediate solution to WEP encryption and data integrity insecurities while the IEEE 802.11i standard was being ratified. When WPA is implemented, access to the WAP is provided only to clients that have the right passphrase. Although WPA is more secure than WEP, if the preshared key is stored on the wireless client and the client is stolen, a hacker could get access to the wireless network. WPA supports both authentication and encryption. Authentication done through preshared keys is known as WPA Personal; when done through 802.1x, it is known as WPA Enterprise. WPA offers Temporal Key Integrity Protocol (TKIP) as an encryption algorithm and a new integrity algorithm known as Michael. WPA is a subset of the 802.11i specification. 802.11iIn June 2004, the IEEE ratified the draft for the 802.11i standard, also known as WPA2. The 802.11i standard formally replaces WEP and other security features of the original IEEE 802.11 standard. WPA2 is the product certification attributed to wireless equipment that is compatible with the 802.11i standard. WPA2 certification provides support for the additional mandatory 802.11i security features that are not included in WPA. WPA2, like WPA, supports both Enterprise and Personal modes for authentication. In addition to stricter encryption requirements, WPA2 also adds enhancements to support fast roaming of wireless clients by allowing a client to preauthenticate with the access point toward which it is moving, while maintaining a connection to the access point that it is moving away from. Wireless Intrusion DetectionMany products provide rogue access point detection. However, some third-party products integrate better than others with Cisco Aironet WAPs and the CiscoWorks Wireless LAN Solution Engine (WLSE), discussed in the next section. One such third-party product is from AirDefense.[5] This product provides wireless intrusion detection that uses the access points to scan the airwaves and report wireless activity. |