A system for location based security which includes a plurality of receivers. Each of the receivers determines times of arrival of received time varying signals. The system also includes a server in communication with the receivers and a mobile device. The server receives the times of arrival from the receivers, and times of arrival of the time varying signals determined by the mobile device. The server determines a location of the mobile device based on the times of arrival. The server may then authorize the mobile device to perform secure communication over the secure communication network when the location of the mobile device is determined to be in an authorized communication area defined based on the times of arrival received from the receivers.