KEY ISSUING METHOD AND GROUP SIGNATURE SYSTEM

摘要

There is provided a key issuing method for issuing a key by a user device connected to an issuing person device via a network. The method includes: a step of reading an issuing person public key from the issuing person device to a user storage unit; a step of receiving first concealed data containing one or more concealed text obtained by subjecting the issuing person public key to concealment processing by using element data containing information on a group element in the issuing person device; a step of generating second concealed data containing a concealed text obtained by a product of power-residue of the element data corresponding to the concealed text contained in the first concealed data by using the issuing person public key and the first concealed data, or concealed text obtained by a sum of element data multiplied by a constant, and transmitting it to the issuing person device; a step of receiving information generated in the issuing person device and based on the element data corresponding to the second concealed data; a step of generating a member public key and a member secret key corresponding to the local device by using the information based on the element data of the second concealed data and writing it into the user storage unit.