Value Matching of Positive Users

To identify any exposures, each client periodically fetches the list of new Diagnosis Keys from the Diagnosis Server. Because Diagnosis Keys are sets of Temporary Exposure Keys with their associated ENIntervalNumber, each of the clients can again derive the sequence of Rolling Proximity Identifiers that were broadcast over Bluetooth from users who tested positive.

To do so, the clients use each of the Diagnosis Keys with the function defined, to derive the 144 Rolling Proximity Identifiers starting from ENIntervalNumber. The clients match each of the derived identifiers against the sequence they found through Bluetooth scanning. A +/- two-hour tolerance window is allowed between when a Rolling Proximity Identifier derived from the Diagnosis Key was supposed to be broadcast, and the time at which it was scanned.

The Associated Encrypted Metadata does not have to be decrypted until a match occurs. Upon decryption, the data has to be appropriately sanitized and validated as the Associated Encrypted Metadata isn’t authenticated.

• Overview

• External Functions

• Key Schedule for Exposure Notification

• Positive Diagnosis

• Value Matching of Positive Users

• Privacy Considerations

• Test Vectors

• Revision History