1. A method of determining a counterfeit security document, the security document having disposed thereon or therein coded data including a plurality of coded data portions, each coded data portion being indicative of: an identity of the security document; and, a signature part, the signature part being a part of a digital signature of at least part of the identity; wherein the method includes steps of: in a sensing device: sensing a plurality of coded data portions; and, generating, using the sensed coded data portions, indicating data indicative of: the identity; the respective signature parts; and an identifier for each signature part: in a processor: determining, from the indicating data: a determined identity; and, a determined signature from the plurality of signature parts by arranging signature parts according to respective identifiers; determining a generated identity from the sensed signature; and determining if the security document is a counterfeit document by comparing the determined identity and the generated identity.