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[ISN] Researchers crack WEP WiFi security in record time
By Peter Sayer
IDG News Service
04 April 2007
The WiFi security protocol WEP should not be relied on to protect
sensitive material, according to three German security researchers who
have discovered a faster way to crack it. They plan to demonstrate their
findings at a security conference in Hamburg this weekend.
Mathematicians showed as long ago as 2001 that the RC4 key scheduling
algorithm underlying the WEP (Wired Equivalent Privacy) protocol was
flawed, but attacks on it required the interception of around 4 million
packets of data in order to calculate the full WEP security key.
Further flaws found in the algorithm have brought the time taken to find
the key down to a matter of minutes, but that's not necessarily fast
enough to break into systems that change their security keys every five
Now it takes just 3 seconds to extract a 104-bit WEP key from
intercepted data using a 1.7GHz Pentium M processor. The necessary data
can be captured in less than a minute, and the attack requires so much
less computing power than previous attacks that it could even be
performed in real time by someone walking through an office.
Anyone using WiFi to transmit data they want to keep private, whether
it's banking details or just email, should consider switching from WEP
to a more robust encryption protocol, the researchers said.
"We think this can even be done with some PDAs or mobile phones, if they
are equipped with wireless LAN hardware," said Erik Tews, a researcher
in the computer science department at Darmstadt University of Technology
in Darmstadt, Germany.
Tews, along with colleagues Ralf-Philipp Weinmann and Andrei Pyshkin,
published a paper about the attack showing that their method needs far
less data to find a key than previous attacks: just 40,000 packets are
needed for a 50 percent chance of success, while 85,000 packets give a
95 percent chance of success, they said.
Although stronger encryption methods have come along since the first
flaws in WEP were discovered over six years ago, the new attack is still
relevant, the researchers said. Many networks still rely on WEP for
security: 59 percent of the 15,000 WiFi networks surveyed in a large
German city in September 2006 used it, with only 18 percent using the
newer WPA (WiFi Protected Access) protocol to encrypt traffic. A survey
of 490 networks in a smaller German city last month found 46 percent
still using WEP, and 27 percent using WPA. In both surveys, over a fifth
of networks used no encryption at all, the researchers said in their
Businesses can still protect their networks from the attack, even if
they use old WiFi hardware incapable of handling the newer WPA
For one thing, the researchers said, their attack is active: in order to
gather enough of the right kind of data, they send out ARP (Address
Resolution Protocol) requests, prompting computers on the network under
attack to reply with unencrypted packets of an easily recognisable
length. This should be enough to alert an IDS (intrusion detection
system) to the attack, they say.
Another way to defeat attacks like that of the Darmstadt researchers,
which use statistical techniques to identify a number of possible keys
and then select the one most likely to be correct for further analysis,
is to hide the real security key in a cloud of dummy ones. That's the
approach taken by AirDefense in its WEP Cloaking product, which was
released Monday. The technique means that businesses can
cost-effectively protect networks using old hardware, such as
point-of-sale systems, without the need to upgrade every terminal or
base station, the company said.
If your network supports WPA encryption, though, you should use that
instead of WEP to protect your private data, Tews said.
"Depending on your skills, it will cost you some minutes to some hours
to switch your network to WPA. If it would cost you more than some hours
of work if such private data becomes public, then you should not use WEP
anymore," he said.
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