An imaging device comprising a controller, a prover supply item and a verifier supply item, where the imaging device is configured to authenticate the prover supply item by: sending a challenge response from the prover supply item to the verifier supply item, and determining a status of the challenge response. When the verifier supply item determines that the received challenge response is a correct output of an algorithm when challenge data is input to the algorithm, the status is determined as verified. A supply item configured to be operable as a prover supply item when installed in an imaging device. The prover supply item is configured to receive an indication of an algorithm to be performed and receive challenge data, perform the algorithm using the challenge data as input to determine a challenge response, and send the challenge response to a verifier supply item.