When a mobile device such as a smart phone comes within range of a location device, the mobile device inputs a location token from the location device and a travel token is created from a mobile device token and the location token. The mobile and location tokens may include data elements indicating not only identity, but also such other characteristics as an authorization or infection risk level. Tokens may be digitally signed, preferably with an independently verifiable signature that also encodes time. Mobile and location devices may be created and issued by a tracking service provider, which may also store tokens, analyze travel tokens with respect to a location's risk level, and update mobile device and location tokens to change a status of the mobile or location device.