An apparatus, comprising: - a communication port; and - a processor coupled to the communication port, the processor configured to: - send a request to a communication partner and receive a response from the communication partner via the communication port; - measure a time period from the request being sent to the response being received; - receive a secondary value from the communication partner via the communication port, the secondary value comprising at least a portion of the request, at least a portion of the response, and a measured time interval from when the communication partner receives a last symbol of the request to when the communication partner starts sending a first symbol of the response, and the secondary value having been sent with authenticating data to authenticate the secondary value; - authenticate the secondary value using the authenticating data and verify that the portion of the request and the portion of the response are included in the secondary value; and - compare the time period with a predefined threshold, wherein the predefined threshold is calculated based on a predefined maximum allowed distance to the communication partner, wherein the request and response are transmitted by modulated signals, wherein each of the modulated signals comprises one or more symbols and the request and response are transmitted by the one or more symbols, and the time period is measured using timings of the one or more symbols. - a communication port; and - a processor coupled to the communication port, the processor configured to: - send a request to a communication partner and receive a response from the communication partner via the communication port; - measure a time period from the request being sent to the response being received; - receive a secondary value from the communication partner via the communication port, the secondary value comprising at least a portion of the request, at least a portion of the response, and a measured time interval from when the communication partner receives a last symbol of the request to when the communication partner starts sending a first symbol of the response, and the secondary value having been sent with authenticating data to authenticate the secondary value; - authenticate the secondary value using the authenticating data and verify that the portion of the request and the portion of the response are included in the secondary value; and - compare the time period with a predefined threshold, wherein the predefined threshold is calculated based on a predefined maximum allowed distance to the communication partner, wherein the request and response are transmitted by modulated signals, wherein each of the modulated signals comprises one or more symbols and the request and response are transmitted by the one or more symbols, and the time period is measured using timings of the one or more symbols. - send a request to a communication partner and receive a response from the communication partner via the communication port; - measure a time period from the request being sent to the response being received; - receive a secondary value from the communication partner via the communication port, the secondary value comprising at least a portion of the request, at least a portion of the response, and a measured time interval from when the communication partner receives a last symbol of the request to when the communication partner starts sending a first symbol of the response, and the secondary value having been sent with authenticating data to authenticate the secondary value; - authenticate the secondary value using the authenticating data and verify that the portion of the request and the portion of the response are included in the secondary value; and - compare the time period with a predefined threshold, wherein the predefined threshold is calculated based on a predefined maximum allowed distance to the communication partner, wherein the request and response are transmitted by modulated signals, wherein each of the modulated signals comprises one or more symbols and the request and response are transmitted by the one or more symbols, and the time period is measured using timings of the one or more symbols.