Crate tcn

Reference implementation of Temporary Contact Numbers, a decentralized, privacy-first contact tracing protocol developed by the TCN Coalition. No personally-identifiable information is required by the protocol, and although it is compatible with a trusted health authority, it does not require one. Users' devices send short-range broadcasts over Bluetooth to nearby devices. Later, a user who develops symptoms or tests positive can report their status to their contacts with minimal loss of privacy. Users who do not send reports reveal no information. Different applications using the TCN protocol can interoperate, and the protocol can be used with either verified test results or for self-reported symptoms via an extensible report memo field.

For more information on the protocol, see the README.

Example

use tcn::*;
// Generate a report authorization key.  This key represents the capability
// to publish a report about a collection of derived temporary contact numbers.
let rak = ReportAuthorizationKey::new(rand::thread_rng());

// Use the temporary contact key ratchet mechanism to compute a list
// of temporary contact numbers.
let mut tck = rak.initial_temporary_contact_key(); // tck <- tck_1
let mut tcns = Vec::new();
for _ in 0..100 {
    tcns.push(tck.temporary_contact_number());
    tck = tck.ratchet().unwrap();
}

// Prepare a report about a subset of the temporary contact numbers.
let signed_report = rak
    .create_report(
        MemoType::CoEpiV1,        // The memo type
        b"symptom data".to_vec(), // The memo data
        20,                       // Index of the first TCN to disclose
        90,                       // Index of the last TCN to check
    )
    .expect("Report creation can only fail if the memo data is too long");

// Verify the source integrity of the report...
let report = signed_report
    .verify()
    .expect("Valid reports should verify correctly");

// ...allowing the disclosed TCNs to be recomputed.
let recomputed_tcns = report.temporary_contact_numbers().collect::<Vec<_>>();

// Check that the recomputed TCNs match the originals.
// The slice is offset by 1 because tcn_0 is not included.
assert_eq!(&recomputed_tcns[..], &tcns[20 - 1..90 - 1]);

Structs

Report	A report of potential exposure.
ReportAuthorizationKey	Authorizes publication of a report of potential exposure.
SignedReport	A signed exposure report, whose source integrity can be verified to produce a Report.
TemporaryContactKey	A ratcheting key used to derive temporary contact numbers.
TemporaryContactNumber	A pseudorandom 128-bit value broadcast to nearby devices over Bluetooth.

Enums

Error	Errors related to the TCN protocol.
MemoType	Describes the intended type of the contents of a memo field.