1. A method of authenticating product packaging, the packaging having disposed thereon or therein coded data including a number of coded data portions, each coded data portion being indicative of: an identity of the packaging; and a part of a signature, the signature being a digital signature of at least a part of the identity of the packaging and comprising a plurality of signature parts; wherein the method includes the steps of: receiving indicating data from a sensing device, the sensing device being responsive to sensing one of the coded data portions to generate the indicating data which is indicative of the identity of the packaging, the part of the signature, and a signature part identifier; determining a determined signature using the identity of the packaging; determining a determined signature part using the determined signature and the signature part identifier; and authenticating the packaging by comparing the determined signature part and the part of the signature.