Weakness Reported in Wireless Security Protocol

By Larry Seltzer  |  Posted 2003-11-06 Print this article Print

Security researcher reports that WPA networks can be compromised through passive sniffing of the network and an offline dictionary attack.

A researcher at ICSA Labs has reported that some implementations of Wi-Fi Protected Access (WPA), a standard for cryptography of data on Wi-Fi networks, can be compromised through a dictionary attack. Robert Moskowitz, senior technical director at ICSA Labs, detailed the attack scenario in a paper published yesterday. Not all WPA-based networks are vulnerable. Those most at risk, according to the paper, are the ones that use the "pre-shared key" method for passphrase generation. Most implementations of WPA, in order to make use of the cryptography accessible to unsophisticated users with normal home computing equipment, allow users to enter a common shared phrase into a WPA user interface on the computer. This phrase, along with the SSID, the visible name for the network, is transformed mathematically into a key used by the cryptography routines. Other key management techniques are available to WPA, but these generally require more expensive and complex network management equipment, such as authentication servers. Moskowitz states that after sniffing a few packets of data from certain points in Wi-Fi standard communication, an attacker could use a "dictionary attack" on the data offline in an attempt to guess the passphrase. Users who employ short, simple passphrases could be quickly cracked. Users who have complex passphrases, such as "elmo2$fruit99.TAMMANY+1875" can feel more secure. According to Moskowitz: "A key generated from a passphrase of less than about 20 characters is unlikely to deter attacks. ... This is considerably longer than most people will be willing to use."
Once the passphrase is guessed, the attacker can join the network like any legitimate user. Moskowitz did not address the use of other techniques, such as MAC address filtering, to stop unauthorized users.
Initial reaction to the report on a Slashdot thread was mixed. Many users pointed out that even a network as vulnerable as those described in the paper is far more secure than the very large number of wireless networks in use today with no cryptographic protection at all. User WolfWithoutAClause remarked that many other protocols are subject to dictionary attacks, and that only long passwords and good password practices can properly address such problems.Discuss This in the eWEEK Forum Security Center Editor Larry Seltzer has worked in and written about the computer industry since 1983.
Larry Seltzer has been writing software for and English about computers ever since—,much to his own amazement—,he graduated from the University of Pennsylvania in 1983.

He was one of the authors of NPL and NPL-R, fourth-generation languages for microcomputers by the now-defunct DeskTop Software Corporation. (Larry is sad to find absolutely no hits on any of these +products on Google.) His work at Desktop Software included programming the UCSD p-System, a virtual machine-based operating system with portable binaries that pre-dated Java by more than 10 years.

For several years, he wrote corporate software for Mathematica Policy Research (they're still in business!) and Chase Econometrics (not so lucky) before being forcibly thrown into the consulting market. He bummed around the Philadelphia consulting and contract-programming scenes for a year or two before taking a job at NSTL (National Software Testing Labs) developing product tests and managing contract testing for the computer industry, governments and publication.

In 1991 Larry moved to Massachusetts to become Technical Director of PC Week Labs (now eWeek Labs). He moved within Ziff Davis to New York in 1994 to run testing at Windows Sources. In 1995, he became Technical Director for Internet product testing at PC Magazine and stayed there till 1998.

Since then, he has been writing for numerous other publications, including Fortune Small Business, Windows 2000 Magazine (now Windows and .NET Magazine), ZDNet and Sam Whitmore's Media Survey.

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