An interface cable is configured to connect a host instrument to a physiological sensor. The interface cable has an ID signal input from the sensor and a LED drive signal input from the host instrument sensor port. The interface cable also has a data signal output to the host instrument sensor port. The LED drive signal and the data signal provide an encrypted handshake to and from the host instrument. The handshake is responsive to the ID signal so as to enable normal operation of the host instrument and the sensor.