October 20, 2017

Blockchains and voting

I’ve been asked about a number of ideas lately involving voting systems and blockchains. This blog piece talks about all the security properties that a voting system needs to have, where blockchains help, and where they don’t.

Let’s start off a decade ago, when Daniel Sandler and I first wrote a paper saying blockchains would be useful for voting systems. We observed that voting machines running on modern computers have overwhelming amounts of CPU and storage, so let’s use it in a serious way. Let’s place a copy of every vote on every machine and let’s use timeline entanglement (Maniatis and Baker 2002), so every machine’s history is protected by hashes stored on other machines. We even built a prototype voting system called VoteBox that used all of this, and many of the same ideas now appear in a design called STAR-Vote, which we hope could someday be used by real voters in real elections.

What is a blockchain good for? Fundamentally, it’s about having a tamper-evident history of events. In the context of a voting system, this means that a blockchain is a great place to store ballots to protect their integrity. STAR-Vote and many other “end-to-end” voting systems have a concept of a “public bulletin board” where encrypted votes go, and a blockchain is the obvious way to implement the public bulletin board. Every STAR-Vote voter leaves the polling place with a “receipt” which is really just the hash of their encrypted ballot, which in turn has the hash of the previous ballot. In other words, STAR-Vote voters all leave the polling place with a pointer into the blockchain which can be independently verified.

So great, blockchain for the win, right? Not so fast. Turns out, voting systems need many additional security properties before they can be meaningfully secure. Here’s a simplified list with some typical vocabulary used for these security properties.

  • Cast as intended. A voter is looking at a computer of some sort and indicates “Alice for President!”, and our computer handily indicates this with a checkbox or some highlighting, but evil malware inside the computer can silently record the vote as “Bob for President!” instead. Any voting system needs a mechanism to defeat malware that might try to compromise the integrity of the vote. One common approach is to have printed paper ballots (and/or hand-marked paper ballots) which can be statistically compared to the electronic ballots. Another approach is to have a process whereby the machine can be “challenged” to prove that it correctly encrypted the ballot (Benaloh 2006, Benaloh 2007).
  • Vote privacy. It’s important that there is no way to identify a particular voter with how they voted. To understand the importance of vote privacy, consider a hypothetical alternate where all votes were published, in the newspaper, with the voter’s name next to each vote. At that point, you could trivially bribe or coerce people to vote in a particular way. The modern secret ballot, also called the Australian ballot, ensures that votes are secret, with various measures taken to make it hard or impossible for voters to violate this secrecy. When you wish to maintain a privacy property in the face of voting computers, that means you have to prevent the computer from retaining state (i.e., keeping a private list of the plaintext votes in the order cast) and you have to ensure that the ciphertext votes, published to the blockchain, aren’t quietly leaking information about their plaintext through various subliminal channels.
  • Counted as cast. If we have voters taking home a receipt of some sort that identifies their ciphertext vote in the blockchain, then they also want to have some sort of cryptographic proof that the final vote tally includes their specific vote. This turns out to be a straightforward application of homomorphic cryptographic primitives and/or mixnets.

If you look at these three properties, you’ll notice that the blockchain doesn’t do much to help with the first two, although they are very useful for the third.

Achieving a “cast as intended” property requires a variety of mechanisms ranging from paper ballots and spot challenges of machines. The blockchain protects the integrity of the recorded vote, but has nothing to say about its fidelity to the intent of the voter.

Achieving a “vote privacy” property requires locking down the software on the voting platform, and for that matter locking down the entire computer. And how can that lock-down property be verified? We need strong attestations that can be independently verified. We also need to ensure that the user cannot be spoofed into running a fake voting application. We can almost imagine how we can achieve this in the context of electronic voting machines which are used exclusively for voting purposes. We can centrally deploy a cryptographic key infrastructure and place physical controls over the motion of the machines. But for mobile phones and personal computers? We simply don’t have the infrastructure in place today, and we probably won’t have it for years to come.

To make matters worse, a commonly expressed desire is to vote from home. It’s convenient! It increases turnout! (Maybe.) Well, it also makes it exceptionally easy for your spouse or your boss or your neighbor to watch over your shoulder and “help” you vote the way they want you to vote.

Blockchains do turn out to be incredibly helpful for verifying a “counted as cast” property, because they force everybody to agree on the exact set of ballots being tabulated. If an election official needs to disqualify a ballot for whatever reason, that fact needs to be public and everybody needs to know that a specific ballot, right there in the blockchain, needs to be discounted, otherwise the cryptographic math won’t add up.

Wrapping up, it’s easy to see how blockchains are an exceptionally useful primitive that can help build voting systems, with particular value in verifying that the final tally is consistent with the cast ballot records. However, a good voting system needs to satisfy many additional properties which a blockchain cannot provide. While there’s an intellectual seduction to pretend that casting votes is no different than moving coins around on a blockchain, the reality of the problem is a good bit more complicated.

Pragmatic advice for buying “Internet of Things” devices

We’re hearing an increasing amount about security flaws in “Internet of Things” devices, such as a “messaging” teddy bear with poor security or perhaps Samsung televisions being hackable to become snooping devices. How are you supposed to make purchasing decisions for all of these devices when you have no idea how they work or if they’re flawed?

Threat modeling and understanding the vendor’s stance. If a device comes from a large company with a reputation for caring about security (e.g., Apple, Google, and yes, even Microsoft), then that’s a positive factor. If the device comes from a fresh startup, or from a no-name Chinese manufacturer, that’s a negative factor. One particular thing that you might look for is evidence that the device in question automatically updates itself without requiring any intervention on your behalf. You might also consider the vendor’s commitment to security features as part of the device’s design. And, you should consider how badly things could go wrong if that device was compromised. Let’s go through some examples.

Your home’s border router. When we’re talking about your home’s firewall / NAT / router box, a compromise is quite significant, as it would allow an attacker to be a full-blown man-in-the-middle on all your traffic. Of course, with the increasing use of SSL-secured web sites, this is less devastating than you’d think. And when our ISPs might be given carte blanche to measure and sell any information about you, you already need to actively mistrust your Internet connection. Still, if you’ve got insecure devices on your home network, your border router matters a lot.

A few years ago, I bought a pricey Apple Airport Extreme, which Apple kept updated automatically. It has been easy to configure and manage and it faithfully served my home network. But then Apple supposedly decided to abandon the product. This was enough for me to start looking around for alternatives, wherein I settled on the new Google WiFi system, not only because it does a clever mesh network thing for whole-home coverage, but because Google explicitly claims security features (automatic updates, trusted boot, etc.) as part of its design. If you decide you don’t trust Google, then you should evaluate other vendors’ security claims carefully rather than just buying the cheapest device at the local electronics store.

Your front door / the outside of your house. Several vendors offer high-tech door locks that speak Bluetooth or otherwise can open themselves without requiring a mechanical key. Other vendors offer “video doorbells”. And a number of IoT vendors have replacements for traditional home security systems, using your Internet connection for connecting to a “monitoring” service (and, in some cases, using a cellular radio connection as a backup). For my own house, I decided that a Ring video doorbell was a valuable idea, based on its various advertised features, but also if it’s compromised, nobody can see into my house. In the worst case, an attacker can learn the times that I arrive and leave from my house, which aren’t exactly a nation-state secret. Conversely, I stuck with our traditional mechanical door locks. Sure, they’re surprisingly easy to pick, but I might at least end up with a nice video of the thief. I’m assuming that I have more to risk from “smash and grab” amateur thieves than from careful professionals. Ultimately, we do have insurance for these sorts of things. Speaking of which, Ring provides a free replacement if somebody steals your video doorbell. That’s as much a threat as anything.

Your home interior. Unlike the outside, I decided against any sort of always-on audio or video devices inside my house. No NestCam. No “smart” televisions. No Alexa or Google Home. After all the hubbub about baby monitors being actively cataloged and compromised, I wouldn’t be willing to have any such devices on my network because the risks outweigh the benefits. On the flip side, I’ve got no problem with my Nest thermostats. They’re incredibly convenient, and the vendor seems to have kept up with software patches and feature upgrades, continuing to support my first-generation devices. If compromised, an attacker might be able to overheat my house or perhaps damage my air conditioner by power-cycling it too rapidly. Possible? Yes. Likely? I doubt it. As with the video doorbell, there’s also a risk that an attacker could profile when I leave in the morning and get home in the evening.

Your mobile phones. The only in-home always-on audio surveillance is the “Ok Google” functionality in our various Android devices, which leads to a broader consideration of mobile phone security. All of our phones are Google Nexus or Pixel devices, so are running the latest release builds from Google. I’d feel similarly comfortable with the latest Apple devices. Suffice to say that mobile phone security is really an entirely separate topic from IoT security, but many of the same considerations apply: is the vendor supplying regular security patches, etc.

Your home theater. As mentioned above, I’m not interested in “smart” devices that can turn into surveillance devices. Our “smart TV” solution is a TiVo device: actively maintained by TiVo, and with no microphone or camera. If compromised, an attacker could learn what we’re watching, but again, there are no deep secrets that need to be protected. (Gratuitous plug: SyFy’s “The Expanse” is fantastic.) Our TV itself is not connected to anything other than the TiVo and a Chromecast device (which, again, has a remarkably limited attack surface; it’s basically just a web browser without the buttons around the edges).

I’m pondering a number of 4K televisions to replace our older TV, and they all come with “smarts” built-in. For most TV vendors, I’d just treat them as “dumb” displays, but I might make an exception for an Android TV device. I’ll note that Google abandoned support for its earlier Google TV systems, including a Sony-branded Google TV Bluray player that I bought back in the day, so I currently use it as a dumb Bluray player rather than as a smart device for running apps and such. My TiVo and Chromecast provide the “smart” features we need and both are actively supported. Suffice to say that when you buy a big television, you should expect it to last a decade or more, so it’s good to have the “smart” parts in smaller/cheaper devices that you can replace or upgrade on a more frequent basis.

Other gadgets. In our home, we’ve got a variety of other “smart” devices on the network, including a Rachio sprinkler controller, a Samsung printer, an Obihai VoIP gateway, and a controller for our solar panel array (powerline networking to gather energy production data from each panel!). The Obihai and the Samsung don’t do automatic updates and are probably security disaster areas. The Obihai apparently only encrypts control traffic with internet VoIP providers, while the data traffic is unencrypted. So do I need to worry about them? Certainly, if an attacker could somehow break in from one device and move laterally to another, the printer and the VoIP devices are the tastiest targets, as an attacker could see what I print (hint: nothing very exciting, unless you really love grocery shopping lists) or listen in on my phone calls (hint: if it’s important, I’d use Signal or I’d have an in-person conversation without electronics in earshot).

Some usability thoughts. After installing all these IoT devices, one of the common themes that I’ve observed is that they all have radically different setup procedures. A Nest thermostat, for example, has you spin the dial to enter your WiFi password, but other devices don’t have dials. What should they do? Nest Protect smoke detectors, for example, have a QR code printed on them which drives your phone to connect to a local WiFi access point inside the smoke detector. This is used to communicate the password for your real WiFi network, after which the local WiFi is never again used. For contrast, the Rachio sprinkler system uses a light sensor on the device that reads color patterns from your smartphone screen, which again send it the configuration information to connect to your real WiFi network. These setup processes, and others like them, are making a tradeoff across security, usability, and cost. I don’t have any magic thoughts on how best to support the “IoT pairing problem”, but it’s clearly one of the places where IoT security matters.

Security for “Internet of Things” devices is a topic of growing importance, at home and in the office. These devices offer all kinds of great features, whether it’s a sprinkler controller paying attention to the weather forecast or a smoke alarm that alerts you on your phone. Because they deliver useful features, they’re going to grow in popularity. Unfortunately, it’s not to possible for most consumers to make meaningful security judgments about these devices, and even web sites that specialize in gadget reviews don’t have security analysts on staff. Consequently, consumers are forced to make tradeoffs (e.g., no video cameras inside the house) or to use device brands as a proxy for measuring the quality and security of these devices.

Engineering around social media border searches

The latest news is that the U.S. Department of Homeland Security is considering a requirement, while passing through a border checkpoint, to inspect a prospective visitor’s “online presence”. That means immigration officials would require users to divulge their passwords to Facebook and other such services, which the agent might then inspect, right there, at the border crossing. This raises a variety of concerns, from its chilling impact on freedom of speech to its being an unreasonable search or seizure, nevermind whether an airport border agent has the necessary training to make such judgments, much less the time to do it while hundreds of people are waiting in line to get through.

Rather than conduct a serious legal analysis, however, I want to talk about technical countermeasures. What might Facebook or other such services do to help defend their users as they pass a border crossing?

Fake accounts. It’s certainly feasible today to create multiple accounts for yourself, giving up the password to a fake account rather than your real account. Most users would find this unnecessarily cumbersome, and the last thing Facebook or anybody else wants is to have a bunch of fake accounts running around. It’s already a concern when somebody tries to borrow a real person’s identity to create a fake account and “friend” their actual friends.

Duress passwords. Years ago, my home alarm system had the option to have two separate PINs. One of them would disable the alarm as normal. The other would sound a silent alarm, summoning the police immediately while making it seem like I disabled the alarm. Let’s say Facebook supported something similar. You enter the duress password, then Facebook locks out your account or switches to your fake account, as above.

Temporary lockouts. If you know you’re about to go through a border crossing, you could give a duress password, as above, or you could arrange an account lockout in advance. You might, for example, designate ten trusted friends, where any five must declare that the lockout is over. Absent those declarations, your account would remain locked, and there would be no means for you to be coerced into giving access to your own account.

Temporary sanitization. Absent any action from Facebook, the best advice today for somebody about to go through a border crossing is to sanitize their account before going through. That means attempting to second-guess what border agents are looking for and delete it in advance. Facebook might assist this by providing search features to allow users to temporarily drop friends, temporarily delete comments or posts with keywords in them, etc. As with the temporary lockouts, temporary sanitization would need to have a restoration process that could be delegated to trusted friends. Once you give the all-clear, everything comes back again.

User defense in bulk. Every time a user, going through a border crossing, exercises a duress password, that’s an unambiguous signal to Facebook. Even absent such signals, Facebook would observe highly unusual login behavior coming from those specific browsers and IP addresses. Facebook could simply deny access to its services from government IP address blocks. While it’s entirely possible for the government to circumvent this, whether using Tor or whatever else, there’s no reason that Facebook needs to be complicit in the process.

So is there a reasonable alternative?

While it’s technically feasible for the government to require that Facebook give it full “backdoor” access to each and every account so it can render threat judgments in advance, this would constitute the most unreasonable search and seizure in the history of that phrase. Furthermore, if and when it became common knowledge that such unreasonable seizures were commonplace, that would be the end of the company. Facebook users have an expectation of privacy and will switch to other services if Facebook cannot protect them.

Wouldn’t it be nice if there was some less invasive way to support the government’s desire for “extreme vetting”? Can we protect ordinary users’ privacy while still enabling the government to intercept people who intend harm to our country? We certainly must assume that an actual bona fide terrorist is going to have no trouble creating a completely clean online persona to use while crossing a border. They can invent wholesome friends with healthy children sharing silly videos of cute kittens. While we don’t know too much about our existing vetting strategies to distinguish tourists from terrorists, we have to assume that the process involves the accumulation of signals and human intelligence, and other painstaking efforts by professional investigators to protect our country from harm. It’s entirely possible that they’re already doing a good job.