Wired Equivalent Privacy (WEP)

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Wired Equivalent Privacy(WEP) is a security algorithm for IEEE 802.11 wireless networks. Introduced as part of the original 802.11 standard ratified in September 1999, its intention was to provide data confidentiality comparable to that of a traditional wired network.[1] In 2003 the Wi-Fi Alliance announced that WEP had been superseded by Wi-Fi Protected Access (WPA). In 2004, with the ratification of the full 802.11i standard (i.e. WPA2), the IEEE declared that both WEP-40 and WEP-104 have been deprecated.[2]

Authentication

Two methods of authentication can be used with WEP: Open System authentication and Shared Key authentication. In Open System authentication, the WLAN client need not provide its credentials to the Access Point during authentication. Any client can authenticate with the Access Point and then attempt to associate. In effect, no authentication occurs. Subsequently WEP keys can be used for encrypting data frames. At this point, the client must have the correct keys. In Shared Key authentication, the WEP key is used for authentication in a four step challenge-response handshake:

  • The client sends an authentication request to the Access Point.
  • The Access Point replies with a clear-text challenge.
  • The client encrypts the challenge-text using the configured WEP key, and sends it back in another authentication request.
  • The Access Point decrypts the response. If this matches the challenge-text the Access Point sends back a positive reply.

After the authentication and association, the pre-shared WEP key is also used for encrypting the data frames using RC4. In cryptography, RC4 (also known as ARC4 or ARCFOUR meaning Alleged RC4, see below) is the most widely used software stream cipher and is used in popular protocols such as Transport Layer Security (TLS) (to protect Internet traffic) and WEP (to secure wireless networks). At first glance, it might seem as though Shared Key authentication is more secure than Open System authentication, since the latter offers no real authentication. However, it is quite the reverse. It is possible to derive the keystream used for the handshake by capturing the challenge frames in Shared Key authentication.[3]Therefore, data can be more easily intercepted and decrypted with Shared-key authentication than with Open System authentication. If privacy is a primary concern, it is more advisable to use Open System authentication for WEP authentication, rather than Shared Key authentication; however this also means that any WLAN client can connect to the AP. (both authentication mechanisms are weak; Shared Key WEP is deprecated in favor of WPA/WPA2.).

Encryption

WEP uses the stream cipher RC4 for confidentiality, and the CRC-32 checksum for integrity. Standard 64-bit WEP uses a 40 bit key (also known as WEP-40), which is concatenated with a 24-bit initialization vector (IV) to form the RC4 key. A 64-bit WEP key is usually entered as a string of 10 hexadecimal (base 16) characters (0-9 and A-F). Each character represents four bits, 10 digits of four bits each gives 40 bits; adding the 24-bit IV produces the complete 64-bit WEP key (4 bits × 10 + 24 bits IV = 64 bit WEP key).[4] A 128-bit WEP key is usually entered as a string of 26 hexadecimal characters. 26 digits of four bits each gives 104 bits; adding the 24-bit IV produces the complete 128-bit WEP key (4 bits × 26 + 24 bits IV = 128 bit WEP key). Most devices also allow the user to enter it as 13 ASCII characters (8 bits × 13 + 24 bits IV = 128 bit WEP key).

Security

RC4 is a stream cipher, the same traffic key must never be used twice. The purpose of an IV, which is transmitted as plain text, is to prevent any repetition, but a 24-bit IV is not long enough to ensure this on a busy network. The way the IV was used also opened WEP to a related key attack. For a 24-bit IV, there is a 50% probability the same IV will repeat after 5000 packets. In August 2001, Scott Fluhrer, Itsik Mantin, and Adi Shamir published a cryptanalysis of WEP that exploits the way the RC4 ciphers and IV are used in WEP, resulting in a passive attack that can recover the RC4 key after eavesdropping on the network. Depending on the amount of network traffic, and thus the number of packets available for inspection, a successful key recovery could take as little as one minute.[5] It is possible to perform the attack with a personal computer, off-the-shelf hardware and freely available software such as aircrack-ng to crack any WEP key in minutes.

Remedies

Use of encrypted tunneling protocols (e.g. IPSec, Secure Shell) can provide secure data transmission over an insecure network. However, replacements for WEP have been developed with the goal of restoring security to the wireless network itself. Ex. 802.11i (WPA and WPA2)[6].

References

  • 1) IEEE Std 802.11-1997 Information Technology- telecommunications And Information exchange Between Systems-Local And Metropolitan Area Networks-specific Requirements-part 11: Wireless Lan Medium Access Control (MAC) And Physical Layer (PHY) Specifications. 1997.
  • 2) "What is a WEP key?". lirent.net. Retrieved 2008-03-11.
  • 3) "Intercepting Mobile Communications: The Insecurity of 802.11". Retrieved 2006-09-12.
  • 4) IEEE 802.11i-2004: Medium Access Control (MAC) Security Enhancements. 2004.
  • 5) SECURITY FLAWS IN 802.11 DATA LINK PROTOCOLS
  • 6) 802.11b Update: Stepping Up Your WLAN Security". networkmagazineindia.com. Retrieved 2008-03-16.