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IEEE 802.11i, also known as WPA2, is an amendment to the 802.11 standard specifying security mechanisms for wireless networks (see Wi-Fi). The draft standard was ratified on 24 June, 2004, and supersedes the previous security specification, Wired Equivalent Privacy (WEP), which was shown to have severe security weaknesses. Wi-Fi Protected Access (WPA) had previously been introduced by the Wi-Fi Alliance as an intermediate solution to WEP insecurities. WPA implemented a subset of 802.11i. The Wi-Fi Alliance refers to their approved, interoperable implementation of the full 802.11i as WPA2. 802.11i makes use of the Advanced Encryption Standard (AES) block cipher; WEP and WPA use the RC4 stream cipher. The 802.11i architecture contains the following components: 802.1X for authentication (entailing the use of EAP and an authentication server), RSN for keeping track of associations, and AES-based CCMP to provide confidentiality, integrity and origin authentication. Another important element of the authentication process is the four-way handshake, explained below. The Four-Way Handshake The authentication process leaves two considerations: the access point (AP) still needs to authenticate itself to the client station (STA), and keys to encrypt the traffic need to be derived. The earlier EAP exchange has provided the shared secret key PMK (Pairwise Master Key). This key is however designed to last the entire session and should be exposed as little as possible. Therefore the four-way handshake is used to establish another key called the PTK (Pairwise Transient Key). The PTK is generated by concatenating the following attributes: PMK, AP nonce (ANonce), STA nonce (SNonce), AP MAC address and STA MAC address. The product is then put through a cryptographic hash function. The handshake also yields the GTK (Group Temporal Key), used to decrypt multicast and broadcast traffic. The actual messages exchanged during the handshake are depicted in the figure and explained below: As soon as the PTK is obtained it is divided into three separate keys: The Group Key Handshake The GTK used in the network may need to be updated due to the expiry of a preset timer. When a device leaves the network, the GTK also needs to be updated. This is to prevent the device from receiving any more multicast or broadcast messages from the AP. To handle the updating, 802.11i defines a Group Key Handshake that consists of a two-way handshake: Security in pre-shared key mode Like WPA, 802.11i has a pre-shared key mode (PSK, also known as personal mode), designed for home and small office networks that cannot afford the cost and complexity of an 802.1X authentication server. Each user must enter a passphrase to access the network. The passphrase is typically stored on the user's computer, so it need only be entered once. The weak passphrases users typically employ create a major vulnerability to password cracking attacks. Passphrases must be at least 8 characters, however at least 20 characters is recommended, and contain numbers and special characters. The IEEE 802.11i standard allows strong PSKs to be entered as 63 character hexadecimal strings. Passphrases should be changed whenever an individual with access is no longer authorized to use the network or when a device configured to use the network is lost or compromised. Security for Public Venues Security for users at public venues have been a unique problem. Venues such as cafes, hotels, airports, malls, libraries, schools, and other public places provide Wi-Fi access to their users. The 802.11i personal mode requires the venue administrator to provide each customer with their personal passphrase. This is an administrative problem and compromises their WLAN for internal use. The enterprise mode is too complex and expensive to manage. Thus, virtually 100% of public venues offer unsecured Wi-Fi. Some venues offer VPN as an option, such as Google WiFi. This solution is expensive to scale. Others such as T-mobile provide a download option that deploys WPA support specific to T-mobile. This conflicts with enterprise configurations at Cisco, IBM, HP, Google, and other large enterprises who have solutions specific to their internal WLAN. Another company, AeONsafe, has a mixed mode 802.11i WiFi for public venues. The security services requires venues to install equipment that includes the AeONsafe, embedded code. The company then provides users with a private key per device. The mixed mode supports Windows, Macintosh, Linux, Palm, and Mobile platforms without software downloads. Devices implementing 802.11i In general, the use of WPA2 needs firmware or driver support of both devices, the wireless host (router or access point) and the wireless client (adapter). Usually, the wireless host can be enabled to support WPA2 by a firmware upgrade, available at the manufacturer's site. The client needs an update of the wireless adapter driver, and maybe part of the operating system as well. Mac OS X With the release of the 4.2 update to their AirPort software, Apple now supports WPA2 on all AirPort Extreme-enabled Macintoshes, the AirPort Extreme Base Station, and the AirPort Express (firmware upgrades included in AirPort 4.2). Windows XP Support of WPA2 needs an operating system update (KB917021 (Replaces KB893357), see external link below), and upgrade of wireless adapter drivers. There is a link to Intel drivers below. Despite security concerns, there is no update for Windows XP x64 to support WPA2. WPA2 support for Windows XP x64 is planned for Windows XP x64 SP2. Linux Support of WPA2 is available. Drivers are needed to support WPA as well as the userspace utility, wpa_supplicant. A Gnome initiative called Network Manager allows users to roam between wireless (WPA2, WPA, WEP and open/unencrypted standards) and wired networks. Mobile, Palm, Symbian Do these platforms support 802.11i? See also | |||||||
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