Privacy-preserving contact tracing

A system comprising:

• at least one device including a hardware processor;
• the system being configured to perform operations comprising:
• generating, by a first user device, a first proximity token for contact tracing;
• receiving, by the first user device, a second proximity token from a second user device;
• generating, by the first user device, a first hash based on the first proximity token and the second proximity token;
• generating, by the first user device using a prover function of a preprocessing zero knowledge succinct non-interactive argument of knowledge (pp-zk-SNARK), a first cryptographic proof attesting that a first individual associated with the first user device tested positive for a pathogen;
• transmitting, by the first user device, first publicly verifiable exposure data comprising at least the first cryptographic proof and the first hash to a public registry;
• generating, by a third user device, a second hash based on proximity tokens from the third user device and a fourth user device;
• checking, by the third user device, a second cryptographic proof using a verifier function of the pp-zk-SNARK, the second cryptographic proof attesting that a third individual associated with a fifth user device had (N-1)th-order contact with the first individual who tested positive for a pathogen;
• and
• based at least on checking the second cryptographic proof, determining, by the third user device, that a fourth individual associated with the third user device had Nth-order contact with the pathogen;
• generating, by the third user device using the prover function of the pp-zk-SNARK, a third cryptographic proof attesting that the fourth individual associated with the third user device had an Nth-order exposure to the pathogen, the third cryptographic proof being a transitive privacy-preserving proof hiding details of intermediate proofs;
• and
• transmitting, by the third user device, second publicly verifiable exposure data comprising at least the fourth cryptographic proof and the second hash to the public registry.

A method comprising:

• generating, by a first user device, a first proximity token for contact tracing;
• receiving, by the first user device, a second proximity token from a second user device;
• generating, by the first user device, a first hash based on the first proximity token and the second proximity token;
• generating, by the first user device using a prover function of a preprocessing zero knowledge succinct non-interactive argument of knowledge (pp-zk-SNARK), a first cryptographic proof attesting that a first individual associated with the first user device tested positive for a pathogen;
• transmitting, by the first user device, first publicly verifiable exposure data comprising at least the first cryptographic proof and the first hash to a public registry;
• generating, by a third user device, a second hash based on proximity tokens from the third user device and a fourth user device;
• checking, by the third user device, a second cryptographic proof using a verifier function of the pp-zk-SNARK, the second cryptographic proof attesting that a third individual associated with a fifth user device had (N-1)th-order contact with the first individual who tested positive for a pathogen;
• and
• based at least on checking the second cryptographic proof, determining, by the third user device, that a fourth individual associated with the third user device had Nth-order contact with the pathogen;
• generating, by the third user device using the prover function of the pp-zk-SNARK, a third cryptographic proof attesting that the fourth individual associated with the third user device had an Nth-order exposure to the pathogen, the third cryptographic proof being a transitive privacy-preserving proof hiding details of intermediate proofs;
• and
• transmitting, by the third user device, second publicly verifiable exposure data comprising at least the fourth cryptographic proof and the second hash to the public registry.