Cryptology ePrint Archive: Report 2020/493

Towards Defeating Mass Surveillance and SARS-CoV-2: The Pronto-C2 Fully Decentralized Automatic Contact Tracing System

Gennaro Avitabile and Vincenzo Botta and Vincenzo Iovino and Ivan Visconti

Abstract: Mass surveillance can be more easily achieved leveraging fear and desire of the population to feel protected while affected by devastating events. Indeed, in such scenarios, governments can adopt exceptional measures that limit civil rights, usually receiving large support from their citizens.

The COVID-19 pandemic is currently affecting daily life of many citizens in the world. People are forced to stay home for several weeks, unemployment rates quickly increase, uncertainty and sadness generate an impelling desire to join any government effort in order to stop as soon as possible the spread of the virus.

Following recommendations of epidemiologists, governments are proposing the use of smartphone applications to allow automatic contact tracing of citizens. Such systems can be an effective way to defeat the spread of the SARS-CoV-2 virus since they allow to gain time in identifying potentially new infected persons that should therefore be in quarantine. This raises the natural question of whether this form of automatic contact tracing can be a subtle weapon for governments to violate the privacy of their citizens as part of new and more sophisticated mass surveillance programs.

In order to preserve privacy and at the same time to contribute to the containment of the pandemic, several research partnerships are proposing privacy-preserving contact tracing systems where pseudonyms are updated periodically to avoid linkability attacks. A core component of such systems is Bluetooth low energy (BLE, for short) a technology that allows two smartphones to detect that they are in close proximity. Among such systems there are some proposals like DP-3T, PACT and the Apple&Google exposure notification system that through a decentralized approach guarantee better privacy properties compared to other centralized approaches (e.g., PEPP-PT-NTK, PEPP-PT-ROBERT). On the other hand, advocates of centralized approaches claim that centralization gives to epidemiologists more useful data, therefore allowing to take more effective actions to defeat the virus.

Motivated by Snowden's revelations about previous attempts of governments to realize mass surveillance programs, in this paper we first analyze mass surveillance attacks that leverage weaknesses of automatic contact tracing systems. We focus in particular on the DP-3T system (still our analysis is significant also for PACT and Apple&Google systems) that has been endorsed by Apple&Google. The endorsement has the impact of integrating in the forthcoming updates of Android and iOS special features like a synchronous rotation of the BLE MAC address of the smartphone with the update of the pseudonyms used in the DP-3T system.

Based on recent literature and new findings, we discuss how a government can exploit the use of DP-3T to successfully mount privacy attacks as part of a mass surveillance program.

Interestingly, we also show that the privacy issues in DP-3T are not intrinsic in any BLE-based contact tracing system. Indeed, we propose a different system named $\textsf{Pronto-C2}$ that, in our view, enjoys a much better resilience with respect to mass surveillance attacks still relying on BLE. $\textsf{Pronto-C2}$ is based on a paradigm shift: instead of asking smartphones to send keys to the Big Brother (this corresponds to the approach of DP-3T), we construct a decentralized BLE-based ACT system where smartphones anonymously and confidentially talk to each other in the presence of the Big Brother.

$\textsf{Pronto-C2}$ can optionally be implemented using Blockchain technology, offering complete transparency and resilience through full decentralization, therefore being more appealing for citizens. Only through a large participation of citizens contact tracing systems can be very useful to defeat COVID-19, and our proposal goes straight in this direction.

Category / Keywords: cryptographic protocols / privacy, blockchain, tracing, BLE, anonymity

Date: received 27 Apr 2020, last revised 6 May 2020

Contact author: gavitabile at unisa it,vbotta@unisa it,viovino@unisa it,visconti@unisa it

Available format(s): PDF | BibTeX Citation

Note: The changes between this and the previous version can be found in Appendix A.

Version: 20200506:135811 (All versions of this report)

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