Proactive quantum secret sharing

A proactive quantum secret sharing scheme is proposed, in which the participants can update their key shares periodically. In an updating period, one participant randomly generates the EPR pairs, and the other participants update their key shares and perform the corresponding unitary operations on the particles of the EPR pairs. Then, the participant who generated the EPR pairs performs the Bell-state measurement and updates his key share according to the result of the Bell-state measurement. After an updating period, each participant can change his key share, but the secret is changeless, and the old key shares will be useless even if they have been stolen by the attacker. The proactive property of our scheme is very useful to resist the mobile attacker.