Let’s Develop Decentralized, Privacy-Preserving Contact Tracing




Over the last few months and especially the last few weeks, the spread of COVID-19 has created a massive health crisis at global scale. Healthcare infrastructure is being overwhelmed around the world. While data about the spread of the virus and its effects are still uncertain, projections about the potential effects of unchecked spread are dire.

Unfortunately, institutional failings have hampered the response to the outbreak of the virus. For instance, Chinese authorities responded to reports of a potential SARS outbreak in early January by arresting eight people for “spreading rumors”. The World Heath Organization announced in mid-January that there was no evidence of human-to-human transmission, ignoring warnings from Taiwanese health authorities sent in December. (Taiwan, which has not had an outbreak, is not allowed to participate in the WHO due to political pressure from China, which views it as a breakaway province). In the US, the CDC prevented testing in the early stages of the outbreak while containment was still possible, and elected officials dumped millions in stock while doing nothing to mobilize resources or prepare a response.

However, we can also observe the power of informal information economies, decentralized responses, and individual actions to step in where institutions fail. While the WHO ignored warnings in January, an informal network of professional and amateur epidemiologists on Twitter and elsewhere tracked the disease’s spread and collected information about the virus. Public outcry helped drive a policy reversal in the UK, where the government had planned to allow the virus to sweep through the population in a plan to “[create] herd immunity, protect the economy, and if that means some pensioners die, too bad” – before belatedly realizing they had done modeling based on a different disease with lower rates of intensive care need than COVID-19.

And some of the highest-impact actions have been the result of individual initiative. Most notably, the outbreak was initially reported by Li Wenliang, who was reprimanded by police and on state television for sharing information on the disease with other doctors. Li contracted COVID-19 while treating patients, and tragically died a month later. And individual researchers with the Seattle Flu Study study, who had been tracking flu outbreaks, made the decision to test existing samples for SARS-CoV-2 without authorization. Before they were ordered to stop, they discovered evidence that the virus had been circulating undetected on the west coast for six weeks. This information may have played a key role in the early timing of the SF Bay Area’s shelter-in-place order.

We are now faced with a global health and economic crisis, which will require full social mobilization to defeat. But just as the impact of COVID-19 cuts across every sector of human activity, so too will the required response, requiring people to think about how the specialized expertise they have can be usefully applied to the problem. We’ve seen people apply 3D printing expertise to produce emergency face shields for hospitals, apply logistics expertise to start spinning up new supply chains, and apply data analysis expertise to make up-to-the-minute information about the outbreak legible. But what kind of role could cryptography usefully play?

One incredibly exciting technological development is TraceTogether, a mobile application that assists with contact tracing produced by the Government of Singapore and the Singapore Ministry of Health (MoH). The app creates a temporary ID by encrypting a user ID to a MoH-owned public key, and then broadcasts the temporary ID over Bluetooth. This temporary ID is refreshed at regular intervals, so that it cannot be used as a long-term identifier for third-party tracking. Nearby mobile devices running the app log all observed broadcasts. If a user later develops symptoms and tests positive for COVID-19, they can upload their log of contacts to the MoH, who functions as a trusted third party that can decrypt the log entries and notify all of that user’s contacts of potential COVID-19 exposure. The MoH promises to use the log data only for the purposes of contact notification.

While this application is not perfectly privacy-preserving, it is far superior to location-tracking, and reveals personal information only upon infection, rather than using the threat of COVID-19 as a justification to build permanent surveillance infrastructure, or exposing patient data to the public. Public health requires public trust, and the developers should be congratulated for building privacy protections into the system.

Unfortunately, most of the world does not have the Singapore Ministry of Health. But removing trusted third parties is a fundamental part of cryptography, and we think this is a problem where the cryptography and privacy community’s skills can be brought to bear. If we had a decentralized, privacy-preserving contact tracing protocol, it could be deployed immediately, without requiring approval or participation of the same institutions that have been ineffective in responding to the crisis. We’ve seen what happened in the aftermath of other crises, like 9/11, where new surveillance infrastructure gave more power to the very institutions whose failure created the crisis. But we don’t have to wait for this to happen and then fight against it. We can build the alternatives we want instead:

We must not forget that we can also build. We carry a new world here, in our hearts. That world is growing in this minute.

At the Zcash Foundation, we’ve been thinking of some ways to solve this problem over the last few days. If you’d like to help, come talk with us and help us solve this problem together.

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