This paper describes techniques to help with COVID-19 automated contact tracing, and with the restoration efforts. We describe a decentralized protocol for "proof-of-contact" (PoC) in zero knowledge where a person can publish a short cryptographic proof attesting to the fact that they have been infected and that they have come in contact with a set of people without revealing any information about any of the people involved. More importantly, we describe how to compose these proofs to support broader functionality such as proofs of nth-order (transitive) exposure which can further speed up automated contact tracing. The cryptographic proofs can be publicly verified. In both cases, the burden (and control) is on (and with) the person proving contact or health and not on (with) third parties or healthcare providers rendering the system more decentralized, and accordingly more scalable.
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