Encryption key distribution system, key distribution server, locking terminal, viewing terminal, encryption key distribution method, and computer-readable medium

A locking terminal for generating an encrypted folder by encrypting a folder, and decrypting the encrypted folder by using a decryption key received from a key distribution server, the locking terminal comprising:

• a locking section that stores thereon an encryption key used to encrypt the folder, and when generating the encrypted folder by encrypting the folder by using the encryption key, writes a user ID of an unlocking right owner who is entitled to decrypt the encrypted folder and a key ID that identifies the encryption key used to encrypt the folder, into the encrypted folder;
• a viewing request section that, when the locking terminal receives a request to view the encrypted folder, reads (i) the user ID of the unlocking right owner who is entitled to decrypt the encrypted folder, (ii) the key ID that identifies the encryption key used to generate the encrypted folder, and (iii) an address of the key distribution server that stores thereon the decryption key corresponding to the key ID, from the encrypted folder, and transmits the read user ID and key ID, to the address of the key distribution server as a viewing request of the encrypted folder;
• and
• an unlocking section, when the locking terminal receives the decryption key from the key distribution server, decrypts the encrypted folder the viewing of which is requested, by using the decryption key received from the key distribution server.

An encryption key distribution method for distributing an encryption key by using a system including therein (i) a locking terminal that stores thereon an encryption key used to encrypt a folder, (ii) a key distribution server that stores thereon, in association with the encryption key, a decryption key used to decrypt the encrypted folder which is generated by using the encryption key, (iii) a viewing terminal that unlocks the encrypted folder, and (iv) a mobile communication terminal that is registered on the key distribution server as an authentication key used to authenticate a user, wherein

• the locking terminal generates the encrypted folder by encrypting the folder by using the encryption key,
• when receiving a request to view the encrypted folder, the viewing terminal transmits a viewing request of the encrypted folder to the key distribution server,
• when receiving the viewing request of the encrypted folder from the viewing terminal, the key distribution server transmits the decryption key to the viewing terminal, under a condition that the key distribution server receives an access from the mobile communication terminal owned by the user who is set as an unlocking right owner of the encrypted folder, and
• when receiving the decryption key corresponding to the encrypted folder the viewing of which is requested from the key distribution server, the viewing terminal unlocks the encrypted folder by using the decryption key.

A computer-readable medium storing thereon a program for a locking terminal for generating an encrypted folder by encrypting a folder, receiving a decryption key used to decrypt the encrypted folder from a key distribution server, and decrypting the encrypted folder by using the decryption key,

• the program causing the locking terminal to realize:
• a locking function of storing an encryption key used to encrypt the folder, and when the locking terminal generates the encrypted folder by encrypting the folder by using the encryption key, writing a user ID of an unlocking right owner who is entitled to decrypt the encrypted folder and a key ID that identifies the encryption key used to encrypt the folder, into the encrypted folder;
• a viewing request function of, when the locking terminal receives a request to view the encrypted folder, reading (i) the user ID of the unlocking right owner who is entitled to decrypt the encrypted folder, (ii) the key ID that identifies the encryption key used to generate the encrypted folder, and (iii) an address of the key distribution server that stores thereon the decryption key corresponding to the key ID, from the encrypted folder, and transmitting the read user ID and key ID, to the address of the key distribution server as a viewing request of the encrypted folder;
• and
• an unlocking function of, when the locking terminal receives the decryption key from the key distribution server, decrypting the encrypted folder the viewing of which is requested, by using the decryption key received from the key distribution server.