CHANGE DIRECTION WITH KEY CONTROL SYSTEM AND CHANGE DIRECTION WITH KEY CONTROL METHOD

摘要

PROBLEM TO BE SOLVED: To enable change with a key of a plurality of times due to information sharing between users, and the control of change direction with a key.SOLUTION: A change direction with key control system 100 includes: a storage part 220 for storing change with a key information which defines the acceptance/rejection of information sharing and a relation of directivity between users, a replacement key for reencoding encoded data of one user so that a decoding key held by the other user can decode the reencoded encoded data, and encoded data by the user; and a change server with a key 200 provided with an arithmetic unit 210 for receiving a transmission request from a user terminal, reencoding encoded data of a prescribed user with a replacement key about between users corresponding to definition in the case that the directivity of information sharing to information sharing possibility from the prescribed user to the other user is defined in the change with a key information, and transmitting the reencoded encoded data to a user terminal of the other user.SELECTED DRAWING: Figure 1