WPA networks open to limited attack

Researchers find more flaws in wireless security


WPA networks open to limited attack

By Robert Lemos, SecurityFocus

Wireless networks that use a popular form of security known as Wi-Fi Protected Access (WPA) are vulnerable to an attack that could compromise certain communications in less than 15 minutes, two researchers plan to tell attendees next week at the PacSec 2008 conference in Tokyo.
Martin Beck and Erik Tews - two graduate students at technical universities in Germany - found a combination of techniques that allow an attacker to decrypt limited communications protected with the lesser of two WPA security protocols, known as the Temporal Key Integrity Protocol or TKIP. Using the techniques, attackers could also recover a special integrity checksum and send up to seven custom packets to clients on the network, sources told SecurityFocus.
The attack does not allow the key protecting the communications to be recovered, one of the researchers stressed .
"The new attack on WPA is not a complete key recovery attack," Tews said in an email to SecurityFocus. "It just allows you to decrypt packets and inject packets with custom content. But there is only a single short-term key recovered during the attack."
The research describes the latest weakness in wireless networks' security. In 2001, three researchers found a way to reliably break the previous wireless security protocol, known as Wired Equivalent Privacy (WEP), in less than two hours. By 2007, the latest refinement in attacks against WEP - found by Tews and two other researchers - reduced the time to recover a WEP key to less than a minute of calculations.
In 2002, after seeing WEP thoroughly broken, the industry alliance responsible for setting standards for wireless access points created the Wi-Fi Protected Access (WPA) protocol. Two years, later the firms created a stronger version of the standard known as WPA2.
Tews and Beck's attack appears to be the first practical, albeit limited, break of WPA encryption.
The duo's attack on WPA's Temporal Key Integrity Protocol (TKIP) uses a similar technique to an attack on WEP found in 2004, according to a copy of Beck's and Tews' presentation obtained by SecurityFocus. The WEP attack, known as chopchop, could decipher a packet of data without knowing the key by guessing each byte and using the access point as a check on each guess: If the packet is accepted by the access point, then the attacker knows the plaintext guess is correct.
The Temporal Key Integrity Protocol (TKIP) adds several countermeasures to foil attacks that would have succeeded against WEP. The protocol adds a message integrity check, or MIC, to protect against header and message alterations and uses replay counters to prevent replay attacks.
The researchers, however, found that the countermeasures only made the attack take longer: a wrong guess would cause the packet to be dropped by the access point, while a correct guess would cause a MIC failure and require the attacker to wait 60 seconds. In the case of an important type of networking data known as an Address Resolution Protocol (ARP) packet, only 14 bytes are not known. In less than 15 minutes, an encrypted ARP packet could be deciphered, including the secret MIC data, according to the researchers' presentation.
The attack also allows a limited amount of data to be sent on other channels using the same keystream - an end run around the replay-attack protection of TKIP.
While the security vulnerabilities are limited, the techniques could be used in a denial-of-service (DoS) attack, the researchers stated in their presentation, by using ARP injection to overwrite entries in the ARP table or potentially attack a local network's domain servers. The technique could also be used to channel data through a corporate firewall, they added.
In an email to a security mailing list, PacSec conference organizer Dragos Ruiu recommended that wireless-network administrators move to WPA2 or use the improved WPA security mode, known as Counter Mode with Cipher Block Chaining Message Authentication Code Protocol (CCMP). In the latter case, the access point should not allow clients to revert to TKIP for communications with legacy systems, Ruiu said.
"If you aren't given the option to disable this, you might want to think about getting a different Access Point or Wi-Fi Router," he said.
According to Tews, an experimental implementation of the researchers' attack has been introduced into a development version of the aircrack-ng tool.
Beck and Tews plan to discuss their findings at the PacSec conference in Tokyo next week.
This article originally appeared in Security Focus.

Researchers find more flaws in wireless security • The Register

While that may be true, to hack the network they need the key. They can listen to the traffic all they want It does them no good If they cant break the encryption-or If it re-keys before enough packets are obtained, The network is still secure. In my case the algorithm for the Temporal key renews every 600 seconds.(by the time they crack the key it would already be changed). Researchers have found a way to break the Temporal Key Integrity Protocol (TKIP) key used by WPA in a matter of twelve to fifteen minutes. This then enables them to send a small number of packets (that could contain malicious code). They have not yet managed to crack the encryption keys used to secure data that goes from the PC to the router. Security experts had known that TKIP could be cracked using what's known as a dictionary attack. Using massive computational resources, the attacker essentially cracks the encryption by making an extremely large number of educated guesses as to what key is being used to secure the wireless data.

"...the frst practical attack on WPA secured wireless networks, besides
launching a dictionary attack when a weak pre shared key (PSK) is used.
The attack works if the network is using TKIP to encrypt the traffic. An
attacker, who has about 12-15 minutes access to the network is then able
to decrypt an ARP request or response and send 7 packets with custom
content to network."

Dictionary/brute force attacks will not crack an encryption key that is random like this, and will have difficulty with a temporal key that renews and changes every 10 minutes:

0z417swWM1'@((H#3$J]{,GOBW248+_@#fsdVXPq34012

Beck-Tews attacks (as well as others) operate on the premise that a long re-keying interval is used for TKIP (i.e., default 3600 seconds), this re-keying Interval must be changed.
The Aircr***-ng cracks utilize WEP (Brute-force search) and WPA (Dictionary File) keys breakers.
Effectively the only way to break WPA is to brute force it, so if you have a long key with letter, numbers and symbols in you are in effect making it logistically impossible to crack. It is important to also set the TKIP renewal to 600 Seconds.

How to secure WPA PSK
1. Block anonymous internet requests
2.You can disable SSID Broadcast (I leave mine enabled though-as it makes it easier to reconnect to network in the event I repair/disconnect from network)
3. Do not use default SSID- change it
4.I use WPA TKP with a randomly manual generated 40+ digit string consisting of Numbers/symbols/letters/caps/lower case-Not an auto generated string (back it up, and
store it somewhere safe- like a encrypted/protected drive)
5.Enable MAC Filtering to allow only those IP's you add to the access list (i.e., networked computers)
6. Disable remote Admin/Disable Remote upgrade/Disable UPnP
7. Set alpha/numeric random password to router that is no less than 8 digits.
8. THIS IS VERY IMPORTANT!-TKIP re-keying Interval must be reset to 600 seconds (or less)

Eircom default wireless configuration is still insecure - boards.ie
http://www.infoworld.com/d/security-central/once-thought-safe-wpa-wi-fi-encryption-cracked-635
http://dl.aircrack-ng.org/breakingwepandwpa.pdf

Great post!