User authentication techniques based on geographical locations associated with a client device is provided. A network connection can be established between two or more host machines and a client device. Upon a request received from the client device by one of these host machines, round trip times of test messages may be measured between the client device and each of the host machines. The round trip times can be utilized to determine the current geographical location of the client device. If the location is within a tolerance geographical area, the client device may be authenticated. Otherwise, the authentication may fail or additional security procedures may be implemented. In some examples, a travel time from a historical geographical location to current geographical location can be determined. This data may be also utilized in the user authentication process.