A method of authenticating an object by sensing coded data provided on or in a surface associated with the object. The coded 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 part of the identity. The method includes using the sensed coded data to determine a sensed identity and a sensed signature part. The sensed identity is then used to determine at least a determined signature part, which is then compared to the sensed signature part, with the object being authenticated using the results of the comparison.