Original URL: http://www.theregister.co.uk/2009/09/23/texas_instruments_calculator_hacking/

Texas Instruments aims lawyers at calculator hackers

Is device modding a punishable offense?

By Dan Goodin

Posted in Policy, 23rd September 2009 03:00 GMT

Lawyers for Texas Instruments are taking aim at a group of calculator enthusiasts who posted the cryptographic keys used to modify the devices so they run custom-designed software.

Over the past few weeks, TI has sent webmasters letters invoking the DMCA, or US Digital Millennium Copyright Act (PDF), and demanding they remove the keys published in blog postings. The private keys are needed to sign operating systems before they work on a wide variety of calculator models designed by the Dallas-based electronics manufacturer.

Because TI generated the keys using extremely weak 512-bit ciphers, the hobbyists were able to crack the vast majority of them in a matter of weeks using an open-source project for distributed computing known as BOINC. The keys make it possible for them to write DIY versions of firmware that in some cases hasn't been updated in more than four years.

"Writing an operating system allows us to use the calculator in ways that are either very difficult or infeasible with TI's operating system," said Brandon Wilson, a 25-year-old programmer who's been writing his own calculator software for about a decade. "By writing our own, we can go about things our own way."

In late August, an attorney sent Wilson a letter warning that a posting on his website ran foul of TI's copyrights because it contained "information that bypasses TI's anti-circumvention technology" that could defeat encryption systems protecting the TI-83 Plus OS. Wilson quickly complied and removed the keys.

On Monday, the attorney struck again, this time against University of Washington student Duncan Smith, who had published the keys' raw materials on ticalc.org, a website dedicated to, well, TI calculators. Smith also took down the posting.

Neither hobbyist consulted with an attorney before caving in to the demands, and that may have been a mistake. According to two attorneys, it's not at all clear TI is using DMCA takedown provisions as Congress intended. What's more, modifications to calculators may be similar to unlocking cell phones, an activity the US Copyright Office has formally exempted from the DMCA.

"When websites publish these cracked keys, the websites aren't violating the copyright per se," said Eric Goldman a professor specializing in cyber law at Santa Clara University. Rather, "they might be violating provisions of the anti-circumvention rules under the copyright act."

While it's clear the DMCA requires websites to remove content that infringes copyright, courts have yet to weigh in on whether those provisions apply to material that makes it possible for others to defeat electronic locks protecting copyrighted works, he added.

Copyright or control?

Another issue clouding the case is whether TI is using the DMCA to protect copyrighted material or merely to control the way its calculators are being used by people who legally own them, said Jennifer Granick, an attorney for the Electronic Frontier Foundation.

"If they're using the DMCA to control the platform rather than to prevent infringement, the courts and the Copyright Office have looked askance at that in the past," said Granick, who was responsible for winning the copyright exemption for unlocking cell phones so they can be used on unauthorized carrier networks. "Users have the right to modify their own devices and their own copies of software to make it work best for them."

Asked what the precise copyright issue was in the DMCA takedown demands, a company spokeswoman said: "TI's graphing calculator software is copyrighted material. In an effort to protect our intellectual property we have sent these notices." She didn't elaborate.

In all, the hobbyists have published 14 private keys used to digitally sign firmware that runs a wide variety of calculators, including the TI-73, TI-83 Plus, TI-84 Plus models. OSes that don't bear the signature will fail to work unless users carry out other, more cumbersome hacks. The private keys were derived by reverse engineering the hardware to discover its public key and then using a series of computing-intensive mathematical factoring operations.

Thirteen of the keys were cracked by 500 networked computers that sieved some 12.5 512-bit integers over a four-week stretch, according to this post by Lionel Debroux, who helped spearhead the project. The 13th integer had to be sieved manually. The project would have been impractical had the keys used more bits.

Despite TI's efforts to keep the keys out of the public limelight, many of them remained available here on the Wikileaks site.

Both Smith and Wilson insist the goal from the start has been to allow them to run customized firmware on their legally purchased calculators. They say TI is using copyright concerns as a red herring to conceal its real motive, which is to prevent the devices from being disqualified in classrooms while tests are being administered.

"TI has the educational market squarely nailed down and they don't have anything to worry about so long as they make sure their calculators can be trusted to be resettable," Smith told The Register. "They've got all the (test) administrators knowing the TI calculators are trustworthy, and they don't want that to be undermined."

TI's website here shows that many of the OSes haven't been updated in years.

Said Wilson: "Their lack of updates and attention to the series is only more motivation for us to come up with our own solution for an operating system." ®