Set of two or more dongles for providing a digital signature,



wherein each dongle holds a secret key,
wherein each dongle is configured to receive a message, to compute a digital signature of the received message using the secret key, and to transmit the computed digital signature,
wherein at least one of the dongles is configured to, before computing the digital signature, verify the presence of at least one other dongle belonging to the set, and to compute the digital signature only upon successful verification of the presence of one or more other dongles.