A method of authenticating an object using a processor that receives indicating data generated in response to sensing of coded data. The indicating data is indicative of an identity of the object and, at least part of a signature, the signature being a digital signature of at least a part of the identity. The processor determines from the indicating data, a received identity and at least one received signature part, and then uses the received identity and a secret key, to determine a determined signature. The determined signature is then compared to the at least one received signature part to authenticate the object.