A method for determining a distance upper bound by a verifier device is described. The method includes measuring a first round-trip time to receive a first response from a target device corresponding to a first message sent to the target device. The method also includes measuring a second round-trip time to receive a second response from the target device corresponding to a second message sent to the target device, the second response being delayed by a processing time multiplier. The method further includes determining a transit time measurement based on the first round-trip time, the second round-trip time and the processing time multiplier. The method additionally includes determining the distance upper bound based on the transit time measurement.