Cryptographic signing of a data item

it is provided a method for performing a cryptographic signing operation of a data item. The method is performed in a server and comprises the steps of: receiving, from a smartcard reader, a request for a data item to be collectively signed, the request comprising an indication of the data item and an identifier of a smartcard, wherein the collective signing requires the use of both a smartcard secret key and a server secret key for the collective signature to be valid; establishing a secure channel with the smartcard; collaborating with the smartcard over the secure channel to provide a collective signature of the data item, wherein the server bases the signature on the data item and a server secret key, wherein the server secret key is specifically associated with the smartcard secret key, resulting in a collective signature; and sending the collective signature to the smartcard reader.