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'Blind to the data': Behind the effort to anonymously track COVID-19 carriers

Startup TripleBlind is part of an effort to alert you if you crossed paths with an infected person. You wouldn't know who the person was, and nor would anyone else.

A city in blue tone with map pins sticking out of the buildings

Kansas City-based encryption startup TripleBlind is working to secure vast amounts of user location data that could be the first large-scale project that enlists people, and their phones, to help trace the spread of coronavirus in the U.S.

Photo: Getty Images

As U.S. tech companies and government agencies rush to use phone location data to fight the spread of COVID-19, they're straddling a volatile line: seeking the benefits that countries across Asia and Europe have reaped by mapping residents' movements and interactions, but without forcing people to divulge intimate details of their whereabouts. This is the challenge — and business opportunity — for firms such as TripleBlind.

The Kansas City-based encryption startup is working to secure vast amounts of user location data collected by Private Kit, an app launched last month by a team of researchers at the Massachusetts Institute of Technology that could be the first large-scale project that enlists people, and their phones, to help trace the spread of coronavirus in the U.S. The effort comes as more than two dozen countries are reportedly deploying cell phone technology to track the spread of the virus.

"We can't do what Singapore and China and others are doing," TripleBlind co-founder Greg Storm said. "Here, we're going to have to make something that will respect people's privacy."

Private Kit, available on both Android and iOS, collects users' GPS data and stores up to a month's worth of it on their phone. When a user tests positive for COVID-19, they can share that data with local health officials as a replacement to the manual "contact tracing" done with paper and pen, in which people recount by memory where they've been. Officials can then use the information to try to identify others who may have come in contact with the person and zero in on geographic hot spots.

Whether the digitization of this process can succeed depends on bureaucratic hurdles as well as a collective trust in the privacy controls that companies such as TripleBlind are safeguarding.

The small company's venture into the center of a public health crisis comes as tech giants tap into their caches of users' location data one after another to analyze the effectiveness of widespread shelter-in-place policies. Facebook unveiled a series of new mapping tools Monday in collaboration with researchers from Carnegie Mellon University, based on user data across the country. Alphabet, meanwhile, is making aggregated location data culled from Google Maps available for download. In both cases, it's the lack of granular information that provides individual anonymity.

Private Kit's goal is more ambitious, and thus its privacy challenge is more fraught. In seeking to thwart the disease's spread but protect trusting users, it must compartmentalize individuals' precise location data while simultaneously avoiding keeping the information in a central place (like a company or government database). The key to the app's success isn't so much what data it collects, but how it stores it.

"We can bring two encrypted objects together and get the answer," Storm said, explaining how the company named itself. "We're blind to the data, the algorithm and the result."

This differs from the approach taken by traditional location data brokers, including those who sell phone-tracking tools to federal law enforcement, whose solution to anonymity is typically to strip out names and other identifying information. As regulators and civil liberties advocates sound alarm bells about the inherent risk of "reidentification" of anonymized location data — if you know where someone lives and where they work, after all, identifying them is simple — encryption technologies are being touted as a solution.

TripleBlind uses what's known as "secure multiparty computation," a form of encryption that enables multiple parties to bring different data points together to analyze them while at the same time not revealing too much information to any one party. As a result, there's no single repository of user data that can be tapped into — or misused. The question is whether this will allow Private Kit to produce actionable information.

Screenshots of TripleBlind An example of how you would get notified if you came into contact with someone who has COVID-19. Screenshot: Courtesy of TripleBlind

In the case of tracking the spread of COVID-19, some experts warn that the GPS data that Private Kit and other contact-tracing apps rely on isn't granular enough to identify instances of possible exposure. While a GPS coordinate can pinpoint a location on a map, it's not precise enough to measure 6 feet between people. Another fundamental challenge is how to reliably measure someone's location indoors, such as in a densely populated apartment building or a hospital where the virus can spread quickly. This has prompted app developers in other countries to use Bluetooth signals instead of traditional GPS data.

More challenging still: for Private Kit to be effective, it must scale up quickly, experts said. Widespread adoption propelled similar efforts in other countries, arming officials with up-to-date information on the spread of the disease while that information still mattered.

'You don't know where you crossed paths'

One built-in feature differentiating Private Kit from other apps is its redaction one of the most concerning location data points: a person's home. Since COVID-19 contact tracing is focused on where people move outside their homes, Private Kit detects and redacts a user's suspected home location based on where they spent the night multiple days in a row. Users also have the option to manually delete individual data points, removing politically sensitive locations such as an abortion clinic or gun store, for example.

For people who haven't downloaded the Private Kit app, but do so once they are tested for COVID-19, there is also an option to import location data from their Facebook or Google Maps apps. Taken together, the information can provide health officials with a composite map of known cases.

The next step is potentially the most powerful, and the one that TripleBlind and the Private Kit team is still figuring out. Once a new coronavirus case is identified, the goal is to pinpoint other users who may have crossed paths with the infected person. The app would check users' location history against known positive cases, helping them decide if they want to get tested themselves — but without providing them enough information to deduce whom they came in contact with.

"You don't know where you crossed paths, just that you have," explained TripleBlind co-founder Riddhiman Das. "The focus of the effort is to allow an individual to determine if they've been exposed."

Threading this needle has proved tricky, Storm said. Public health officials have warned the Private Kit technologists that they cannot alert a user about a potential exposure unless they are certain that the user came close enough to a person with COVID-19 to justify getting tested. Being in the same grocery store, for example, is not enough.

"We're getting enormous pushback from the health care providers on this," Storm said, citing the back and forth with health officials as the primary reason the next stage of functionality for the Private Kit app remains a work in progress. "The architecture around that exposure function needs some good thinking."

Neither Storm nor Das have a background in encryption. What the VC-backed duo do have is experience developing apps, which they say has proven instrumental in recent weeks. They started working with Ramesh Raskar, a computer vision professor at MIT who previously worked at Google X and Facebook, at the end of last year. In late February, when the White House appointed Mike Pence as coronavirus czar, TripleBlind's team brainstormed with Raskar about how to take the same approach to contact tracing that other countries have mandated.

The first draft of the Private Kit app came together in less than a week in early March, Das said, with contributions from a growing team of software engineer volunteers that recently surpassed 600 people. With the app's intellectual property donated to MIT and the formation of a nonprofit entity to maintain it in the works, the team is focused on rolling out different versions of the app across the world, each with its own requirements.

In recent weeks there have been virtual meetings with the World Health Organization and government officials in India, Chile, Italy and Haiti, Storm said. That's in addition to U.S. pilot projects with the Mayo Clinic and hospitals in Rhode Island, Boston and Kansas City. Each presents different security concerns: Officials in India, for example, don't want users to be able to redact location information. And in Haiti, where network connectivity can be an issue, TripleBlind is scaling down the encryption process to require less computing power.

"We're calling it 'decent privacy,' where it takes 10 days to crack the location and time of a person," Das said. He referred to the version being piloted in the U.S. as the "bullet-proof" option.

'They should be publishing things out front'

It's difficult to assess just how bullet-proof TripleBlind's encryption is, however, because the company doesn't make many technical details public. TripleBlind filed a handful of patents last month, Storm said, describing the technology in general terms but declining to provide specific details. (The filings are not yet publicly available.)

This has raised eyebrows in the close-knit cryptography community. Protocol shared TripleBlind's marketing materials and general patent descriptions with six independent cybersecurity experts. They all said that while the general approach and type of encryption made practical sense, it wasn't clear if what TripleBlind offers is unique.

The same can be said for Private Kit, which published a GitHub repository on an MIT website that experts said offers few details of what information is shared by the app with third parties — and when. MIT staff working on the Private Kit app did not respond to requests for comment for this story.

"If you look at the white paper it's extremely vague. It doesn't tell you how they would accomplish anything. It just lists out the goals, which anyone could do after thinking about it for a couple hours," said Bennett Cyphers, a staff technologist at the Electronic Frontier Foundation. "If you are trying to pitch something as privacy preserving, and you aren't publishing about how it actually works, that's a red flag. They should be publishing things out front and being like, 'Hey, look at our cool technology.'"

Any success Private Kit has in the coming months could reflect well on TripleBlind's commercial business efforts, something its founders don't shy away from. The company had planned to raise a series A round of funding this year, but pushed that off to focus on gaining traction through coronavirus applications. "We are essentially doing it as a humanitarian project," Das said. "To show that you can do this while preserving privacy and helping with the pandemic. And to showcase our technical skills."

Eventually, TripleBlind wants to apply the same approach it's bringing to contact tracing to other sensitive data projects in the health care and financial services industries. "We're trying to take the friction out of interacting algorithms and data," Storm said. "Anywhere with privacy regulations — HIPAA, California's Consumer Privacy Act , and the GDPR in Europe — we're making it easier to do business."


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Dan Bogdanov, a leading multiparty computation encryption expert who has worked on DARPA research projects with the U.S. Defense Department and is now at the security firm Cybernetica in Estonia, stressed that encryption is only part of the puzzle in such projects. Safeguards must be built into how the data is accessed and stored by end users, such as health care providers in the case of Private Kit.

"There's a risk anytime you have a technology but try and whitewash it with a good cause," Bogdanov said. "My desire would be that once the crisis has passed, if companies have built anything that infringes on people's privacy, they should tear down that infrastructure. But can we be certain that happens?"

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