A method of authenticating an object is disclosed. Coded data portions are provided on a surface of the object. Each coded data portion encodes a position of coded data portion on the surface, an identity associated with the object and a signature fragment. The signature fragment is a fragment of a digital signature of at least part of the identity associated with the object. Next, indicating data is received from a sensing device in response to the sensing device sensing coded data portions. The indicating data is representative of the data encoded in the coded data portions sensed by the sensing device. From the indicating data the identity associate with the object, a plurality of signature fragments encoded in respective coded data portions, and the position of respective coded data portions are determined. A signature fragment identifier for respective signature fragments is determined from the respective positions. Also, a determined signature is determined by arranging the signature fragments according to their respective signature fragment identifiers. The determined signature is decrypted to obtain a determined identity. The object is authenticated by comparing the identity to the determined identity.