May 25, 2017

Archives for October 2010

Court permits release of unredacted report on AVC Advantage

In the summer of 2008 I led a team of computer scientists in examining the hardware and software of the Sequoia AVC Advantage voting machine. I did this as a pro-bono expert witness for the Plaintiffs in the New Jersey voting-machine lawsuit. We were subject to a Protective Order that, in essence, permitted publication of our findings but prohibited us from revealing any of Sequoia’s trade secrets.

At the end of August 2008, I delivered my expert report to the court, and prepared it for public release as a technical report with the rest of my team as coauthors. Before we could release that report, Sequoia intervened with the Court, claiming that we were revealing trade secrets. We had been very careful not to reveal trade secrets, so we disputed Sequoia’s claim. In October 2008 the Court ruled mostly in our favor on this issue, permitting us to release the report with some redactions,and reserving a decision on those redacted sections until later.

The hearing on those sections has finally arrived, completely vindicating our claim that the original report was within the parameters of the Protective Order. On October 5, 2010 Judge Linda Feinberg signed an order permitting me to release the original, unredacted expert report, which is now available here.

If you’re curious, you can look at paragraphs 19.8, 19.9, 21.3, and 21.5, as well as Appendices B through G, all of which were blacked out in our previously released report.

HTC Willfully Violates the GPL in T-Mobile's New G2 Android Phone

[UPDATE (Oct 14, 2010): HTC has released the source code. Evidently 90-120 days was not in fact necessary, given that they managed to do it 7 days after the phone’s official release. It is possible that the considerable pressure from the media, modders, kernel copyright holders, and other kernel hackers contributed to the apparently accelerated release.]

[UPDATE (Nov 10, 2010): The phone has been permanently rooted.]

Last week, the hottest new Android-based phone arrived on the doorstep of thousands of expectant T-Mobile customers. What didn’t arrive with the G2 was the source code that runs the heart of the device — a customized Linux kernel. Android has been hailed as an open platform in the midst of other highly locked-down systems, but as it makes its way out of the Google source repository and into devices this vision has repeatedly hit speedbumps. Last year, I blogged about one such issue, and to their credit Google sorted out a solution. This has ultimately been to everyone’s benefit, because the modified versions of the OS have routinely enabled software applications that the stock versions haven’t supported (not to mention improved reliability and speed).

When the G2 arrived, modders were eager to get to work. First, they had to overcome one of the common hurdles to getting anything installed — the “jailbreak”. Although the core operating system is open source, phone manufacturers and carriers have placed artificial restrictions on the ability to modify the basic system files. The motivations for doing so are mixed, but the effect is that hackers have to “jailbreak” or “root” the phone — essentially obtain super-user permissions. In 2009, the Copyright Office explicitly permitted such efforts when they are done for the purpose of enabling third-party programs to run on a phone.

G2 owners were excited when it appeared that an existing rooting technique worked on the G2, but were dismayed when their efforts were reversed every time the phone rebooted. T-Mobile passed the buck to HTC, the phone manufacturer:

The HTC software implementation on the G2 stores some components in read-only memory as a security measure to prevent key operating system software from becoming corrupted and rendering the device inoperable. There is a small subset of highly technical users who may want to modify and re-engineer their devices at the code level, known as “rooting,” but a side effect of HTC’s security measure is that these modifications are temporary and cannot be saved to permanent memory. As a result the original code is restored.

As it turned out, the internal memory chip included an option to make certain portions of memory read-only, which had the effect of silently discarding all changes upon reboot. However, it appears that this can be changed by sending the right series of commands to the chip. This effectively moved the rooting efforts into the complex domain of hardware hacking, with modders trying to figure out how to send these commands. Doing so involves writing some very challenging code that interacts with the open-source Linux kernel. The hackers haven’t yet succeeded (although they still could), largely because they are working in the dark. The relevant details about how the Linux kernel has been modified by HTC have not been disclosed. Reportedly, the company is replying to email queries with the following:

Thank you for contacting HTC Technical Assistance Center. HTC will typically publish on developer.htc.com the Kernel open source code for recently released devices as soon as possible. HTC will normally publish this within 90 to 120 days. This time frame is within the requirements of the open source community.

Perhaps HTC (and T-Mobile, distributor of the phone) should review the actual contents of the GNU Public License (v2), which stipulate the legal requirements for modifying and redistributing Linux. They state that you may only distribute derivative code if you “[a]ccompany it with the complete corresponding machine-readable source code.” Notably, there is no mention of a “grace period” or the like.

The importance of redistributing source code in a timely fashion goes beyond enabling phone rooting. It is the foundation of the “copyleft” regime of software licensing that has led to the flourishing of the open source software ecosystem. If every useful modification required waiting 90 to 120 days to be built upon, it would have taken eons to get to where we are today. It’s one thing for a company to choose to pursue the closed-source model and to start from scratch, but it’s another thing for it to profit from the goodwill of the open source community while imposing arbitrary and illegal restrictions on the code.

Hacking the D.C. Internet Voting Pilot

Editor’s Note: On November 1, 2012, Alex Halderman and several other experts participated in a live streaming symposium on the state of electronic voting in Election 2012: E-Voting: Risk and Opportunity (archived video now available). The event was hosted by the Center for Information Technology Policy at Princeton.

The current U.S. e-voting system is a patchwork of locally implemented technologies and procedures — with varying degrees of reliability, usability, and security. Different groups have advocated for improved systems, better standards, and new approaches like internet-based voting. Panelists will discuss these issues and more, with a keynote by Professor Ron Rivest, one of the pioneers of modern cryptography.

[Update (6/2012): We’ve published a detailed technical paper about the D.C. hack.]

The District of Columbia is conducting a pilot project to allow overseas and military voters to download and return absentee ballots over the Internet. Before opening the system to real voters, D.C. has been holding a test period in which they’ve invited the public to evaluate the system’s security and usability.

This is exactly the kind of open, public testing that many of us in the e-voting security community — including me — have been encouraging vendors and municipalities to conduct. So I was glad to participate, even though the test was launched with only three days’ notice. I assembled a team from the University of Michigan, including my PhD students, Eric Wustrow and Scott Wolchok, and Dawn Isabel, a member of the University of Michigan technical staff.

Within 36 hours of the system going live, our team had found and exploited a vulnerability that gave us almost total control of the server software, including the ability to change votes and reveal voters’ secret ballots. In this post, I’ll describe what we did, how we did it, and what it means for Internet voting.

D.C.’s pilot system

The D.C. system is built around an open source server-side application developed in partnership with the TrustTheVote project. Under the hood, it looks like a typical web application. It’s written using the popular Ruby on Rails framework and runs on top of the Apache web server and MySQL database.

Absentee overseas voters receive a physical letter in the mail instructing them to visit a D.C. web site, http://www.dcboee.us/DVM/, and log in with a unique 16-character PIN. The system gives voters two options: they can download a PDF ballot and return it by mail, or they can download a PDF ballot, fill it out electronically, and then upload the completed ballot as a PDF file to the server. The server encrypts uploaded ballots and saves them in encrypted form, and, after the election, officials transfer them to a non-networked PC, where they decrypt and print them. The printed ballots are counted using the same procedures used for mail-in paper ballots.

A small vulnerability, big consequences

We found a vulnerability in the way the system processes uploaded ballots. We confirmed the problem using our own test installation of the web application, and found that we could gain the same access privileges as the server application program itself, including read and write access to the encrypted ballots and database.

The problem, which geeks classify as a “shell-injection vulnerability,” has to do with the ballot upload procedure. When a voter follows the instructions and uploads a completed ballot as a PDF file, the server saves it as a temporary file and encrypts it using a command-line tool called GnuPG. Internally, the server executes the command gpg with the name of this temporary file as a parameter: gpg […] /tmp/stream,28957,0.pdf.

We realized that although the server replaces the filename with an automatically generated name (“stream,28957,0” in this example), it keeps whatever file extension the voter provided. Instead of a file ending in “.pdf,” we could upload a file with a name that ended in almost any string we wanted, and this string would become part of the command the server executed. By formatting the string in a particular way, we could cause the server to execute commands on our behalf. For example, the filename “ballot.$(sleep 10)pdf” would cause the server to pause for ten seconds (executing the “sleep 10” command) before responding. In effect, this vulnerability allowed us to remotely log in to the server as a privileged user.

Our demonstration attacks

D.C. launched the public testbed server on Tuesday, September 28. On Wednesday afternoon, we began to exploit the problem we found to demonstrate a number of attacks:

  • We collected crucial secret data stored on the server, including the database username and password as well as the public key used to encrypt the ballots.
  • We modified all the ballots that had already been cast to contain write-in votes for candidates we selected. (Although the system encrypts voted ballots, we simply discarded the encrypted files and replaced them with different ones that we encrypted using the same key.) We also rigged the system to replace future votes in the same way.
  • We installed a back door that let us view any ballots that voters cast after our attack. This modification recorded the votes, in unencrypted form, together with the names of the voters who cast them, violating ballot secrecy.
  • To show that we had control of the server, we left a “calling card” on the system’s confirmation screen, which voters see after voting. After 15 seconds, the page plays the University of Michigan fight song. Here’s a demonstration.

Stealthiness wasn’t our main objective, and our demonstration had a much greater footprint inside the system than a real attack would need. Nevertheless, we did not immediately announce what we had done, because we wanted to give the administrators an opportunity to exercise their intrusion detection and recovery processes — an essential part of any online voting system. Our attack remained active for two business days, until Friday afternoon, when D.C. officials took down the testbed server after several testers pointed out the fight song.

Based on this experience and other results from the public tests, the D.C. Board of Elections and Ethics has announced that they will not proceed with a live deployment of electronic ballot return at this time, though they plan to continue to develop the system. Voters will still be able to download and print ballots to return by mail, which seems a lot less risky.

D.C. officials brought the testbed server back up today (Tuesday) with the electronic ballot return mechanism disabled. The public test period will continue until Friday, October 8.

What this means for Internet voting

The specific vulnerability that we exploited is simple to fix, but it will be vastly more difficult to make the system secure. We’ve found a number of other problems in the system, and everything we’ve seen suggests that the design is brittle: one small mistake can completely compromise its security. I described above how a small error in file-extension handling left the system open to exploitation. If this particular problem had not existed, I’m confident that we would have found another way to attack the system.

None of this will come as a surprise to Internet security experts, who are familiar with the many kinds of attacks that major web sites suffer from on a daily basis. It may someday be possible to build a secure method for submitting ballots over the Internet, but in the meantime, such systems should be presumed to be vulnerable based on the limitations of today’s security technology.

We plan to write more about the problems we found and their implications for Internet voting in a forthcoming paper.


Professor J. Alex Halderman is a computer scientist at the University of Michigan.