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Apple's screw-up leaves tethered iPhones easily crackable

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iPhones being used as Wi-Fi hotspots are open to attack because of lax security protocols in the automatic password generation system Apple has in place, according to new research from the University of Erlangen in Germany.

The paper, "Usability vs. Security: The Everlasting Trade-Off in the Context of Apple iOS Mobile Hotspots" by Andreas Kurtz, Felix Freiling, and Daniel Metz, found that the seemingly random password iOS generates for hotspots is simple to crack. It consists of four to six characters followed by a four-digit number string.

As a test, the team downloaded a 52,500-word dictionary from an open source version of Scrabble, added number-generating code, and cracked the iOS password system every time – although the team points out it isn't suggesting Apple used the same dictionary. Using a AMD Radeon HD 6990 GPU, the average time to crack was 59 minutes – which is interesting, but hardly practical.

So the team then reverse-engineered the iOS word list used for password generation, using "static and dynamic analysis," tools like GNU Debugger, and by manually going through the ARM disassembly of the relevant iOS frameworks. They found Apple uses English-language words of between four and six letters from a dictionary copyrighted by Lernout & Hauspie Speech Products.

"Only 1,842 different entries of that dictionary are taken into consideration," the paper states. "Consequently, any default password used within an arbitrary iOS mobile hotspot, is based on one of these 1,842 different words. This fact reduced the search space of our initial brute force attack by more than 96% and thus increased the overall cracking speed significantly."

In addition, the selection of words picked for passwords was skewed. "Suave" was used 0.08 per cent of the time, "subbed" cropped up 0.76 per cent and "head" 0.53 per cent – ten times the frequency they should have had under a random pick. By frontloading these selections into any attack code, the chances of cracking the system quickly are greatly increased.

The team also decided to upgrade their hardware to bring down search times and built a box with four AMD Radeon HD 7970 units that could burn through 390,000 guesses per second. This cut the time to crack automatically generated passwords down to 24 seconds, or 52 using a single AMD Radeon HD 6990 GPU. Users should specify their own the team recommends.

As a test case, the team built an iOS application dubbed "Hotspot Cracker" which could be used to try out an attack of the target phone. This was limited by the processing power of the smartphone, but can be used in conjunction with a cloud password cracking service such as CloudCracker for better results.

Once the password has been cracked, the operator can piggyback on the hotspot's bandwidth, stage a man-in-the-middle attack for eavesdropping, and get access to files stored on the device. Jailbroken iPhones are extra risky since they could allow access to the basic iPhone system services code.

While the researchers concentrated on Apple, they note that other mobile operating systems shouldn't get too smug. Microsoft's Windows Phone 8 uses a similar password system that doesn't even use words, relying instead on eight-digit number strings alone. Android is much better, but there have been cases of manufacturers such as HTC dumbing down password generation for some handsets, the authors report.

"The results of our analysis have shown that the mobile hotspot feature of smart devices increases the attack surface in several ways," the team concludes. "As the default password of an arbitrary iOS hotspot user can be revealed within seconds, attacks on mobile hotspots might have been underestimated in the past and might be an attractive target in the future." ®

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