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The use of wireless technology has become increasingly popular due to its flexibility and recent affordabili ty over traditional methods to access hard-wired LANs. This convenience, however, may not be worth the potential for losses incurred by its use. The 802.11b standard has been coming under increased scrutiny in light of a recently published paper outlining a significant vulnerability found with the Wired Equivalent Privacy (WEP) used to secure traffic between wireless devices. Unfortunately, this recent discovery is the latest in an increasingly long list of security issues surrounding 802.11b. This paper will present the issues surrounding newly discovered vulnerabilities with WEP, as well as current access control problems that exist with the wireless architecture currently in use. It will also propose methods that can be used to help secure wireless LANs. Introduction Wireless connectivity offers a freedom and flexibility never before encountered with home and business users. Traditionally, adding users to a network required wiring to be pulled throughout a building and installed by either a hired professional, or an unfortunate network administrator who had been given the task and a crimping tool. On the other hand, with wireless technology, data travels through the air, allowing a user the ability to connect in locations once deemed impossible, or at the very least inconvenient, to the typical hard-wired user. This newly found freedom, though, has come with a price. Serious security concerns over 802.11b and WEP have been uncovered that have required a moment of pause for those responsible for such wireless installations to determine if the security of a wireless LAN could potentially be sacrificed for the sake of convenience. These concerns, though, don’t seem to be deterring the sales or popularity of 802.11b, as the number of wireless devices is expected to grow from 2.6 million in 2000 to 11.8 million by 2003 [LAW]. Weakness of WEP Wireless technology uses Wired Equivalent Privacy (WEP) as a method of encrypting and decrypting wireless communications typically between a client and an access point connected to a wired LAN. WEP depends on the use of a secret key to encrypt and decrypt packets traveling between the wireless network card and access point. This encryption and decryption takes place using the Ron’s Code 4 (RC4) algorithm, which was designed in 1987, and kept secret until © S A N S In st itu te 2 00 1, A ut ho r r et ai ns fu ll ri gh ts Key fingerprint = AF19 FA27 2F94 998D FDB5 DE3D F8B5 06E4 A169 4E46 Key fingerprint = AF19 FA27 2F94 998D FDB5 DE3D F8B5 06E4 A169 4E46 © SANS Institute 2001, As part of the Information Security Reading Room. Author retains full rights. it was anonymously posted in 1994 [FLU]. The following is a brief overview of the process of WEP to use as a foundation of recently discovered vulnerabilities. The process of encrypting an 802.11 frame is essentially a 3 step process. For the purpose of this discussion, we will assume the use of a 40-bit key. In the first step, WEP computes a 32-bit cyclical redundancy check (ICV) on the payload of the frame and appends it to the end of the frame. Next, one of potentially up to four keys, which are all shared between Wireless LAN (WLAN) members, is selected and appended to a 24-bit initialization vector (IV). One of the problems with WEP is the use (or misuse) of the IV. Typically, the IV selected by the wireless NIC starts at some pre-determined number (such as 0) and incr mented by one for each packet that is transmitted [ARB]. One problem is that each time a card is re-initialized, the IV is reset to the starting number, leaving the possibility of low numbered IV to be re-used more frequently [ARB]. Using the data frame+ICV, and the secret key+IV, the message gets encrypted using the RC4 algorithm. This is accomplished by creating a keystream using the secret key+IV and XORing the keystream with th data payload. The frame that is sent is the resulting ciphertext and the IV. It should be noted for clarity that the IV, in addition to the header and keynumber, is sent in the unencrypted portion of the frame. The receiving station uses the sent IV and the shared secret key to decrypt the ciphertext, again using RC4 to accomplish this. Example of WEP encryption and format of WEP frame [NEW] Serious problems surrounding the use of wireless LANs and specifically WEP have come to light recently. Researchers from UC Berkeley and Zero-Knowledge Systems released a paper outlining the vulnerability of keystream reuse attributed to mismanagement of IV. It was noted that all possible IV could be exhausted in as little as 5 hours [BO2]. This would allow the potential for an attacker to capture two encrypted packets using the same keystream. This flaw could allow an attacker to not only decrypt the contents of an encrypted packet, it could also allow an attacker to insert or change traffic, redirect decrypted traffic to an alternate IP address, or even enable an attacker to develop an IV dictionary to use to decrypt any and all traffic traveling within a wireless network [BO1]. IV Key ICV Payload ICV Payload RC4 24-bit 40-bit