Patent ID: 8886931
Filing Date: 2014-11-11
Classification: H04L,H04W

Abstract:
1. A key sharing system with communication terminals which belong to a same group, and a management device which holds information for sharing a group shared key among said communication terminals, wherein a first communication terminal among said communication terminals comprises; a group shared key storage device that stores said group shared key; a terminal individual information generation device that generates terminal individual information individually for each second communication terminal among said communication terminals; a terminal individual information storage device that stores said terminal individual information; a terminal key information generation device that generates terminal key information individually for each of said second communication terminals, using said terminal individual information; a terminal key information transmission device that transmits said terminal key information to said second communication terminal; an encryption information generation device that generates common encryption information for said second communication terminals, using said terminal individual information; an encryption device that encrypts said group shared key, using said encryption information; and an encrypted shared key information transmission device that transmits encrypted shared key information obtained in said encryption to said management device, and said management device comprises: an encrypted shared key information receiving device that receives encrypted shared key information from said first communication terminal; an encrypted shared key information storage device that stores said received encrypted shared key information; and an encrypted shared key information transmission device that transmits encrypted shared key information stored in said encrypted shared key information storage device to said second communication terminal, and said second communication terminal comprises: a terminal key information receiving device that receives terminal key information from said first communication terminal; an encrypted shared key information receiving device that receives encrypted shared key information from said management device; and a decryption device that restores said group shared key, using said received terminal key information and said received encrypted shared key information, and when a situation arises where at least one of said second communication terminals departs from said group, said first communication terminal: updates encryption information, using the terminal individual information of said second communication terminals other than said at least, one of said second communication terminals; transmits encrypted shared key information, in which said group shared key is encrypted using the updated encryption information, to said management device; and updates the encrypted shared key information to be stored in said management device.