Patent ID: 9258283
Filing Date: 2016-02-09
CPC Classification: G05B,H04L

Claim Text:
1. A key management system for writing, into a home appliance, a second key to be used in cryptographic communication between the home appliance and a second server, by using a mobile information terminal that communicates with (a) a first server managing a master key and (b) the second server managing a first key and the second key, the key management system comprising: the mobile information terminal; and the home appliance, wherein the home appliance includes: a computer processor; and a non-transitory computer-readable medium having stored thereon executable instructions that, when executed by the computer processor, cause the home appliance to function as: a communication unit configured to communicate with the mobile information terminal; a master key storage region in which the master key is previously stored; a service key storage region in which the first key and the second key are to be stored; a key writing processing unit configured to write, into the service key storage region, one of (a) the first key encrypted by the master key and (b) the second key encrypted by the master key, only when the communication unit receives the one of (a) the first key and (b) the second key; and a cryptographic processing unit configured to perform cryptographic processing using one of (i) the master key stored in the master key storage region and (ii) the one of the first key and the second key which is stored in the service key storage region, when the mobile information terminal receives, from one of the first server and the second server, the first key encrypted by the master key managed in the first server, the mobile information terminal transmits (a) the first key encrypted by the master key and (b) a request for writing of the first key, when the communication unit receives the first key encrypted by the master key and the request for writing of the first key from the mobile information terminal, the cryptographic processing unit is configured to decrypt the first key by the master key stored in the master key storage region, and the key writing processing unit is configured to write the decrypted first key to the service key storage region, when the mobile information terminal receives, from the second server, the second key encrypted by the first key managed in the second server, the mobile information terminal transmits, to the communication unit, the second key encrypted by the first key, when the communication unit receives, from the mobile information terminal, the second key encrypted by the first key, the cryptographic processing unit is configured to decrypt the second key by the first key stored in the service key storage region, the home appliance holds the decrypted second key, the mobile information terminal transmits, to the communication unit, a request for reading of the second key held in the home appliance, when the communication unit receives, from the mobile information terminal, the request for reading of the second key, the cryptographic processing unit is configured to encrypt, by the master key stored in the master key storage region, the second key held in the home appliance, and the second key encrypted by the master key is transmitted to the mobile information terminal, the mobile information terminal receives, from the communication unit, the second key encrypted by the master key, and transmits, to the communication unit, the second key and a request for writing of the second key, and when the communication unit receives, from the mobile information terminal, the second key encrypted by the master key and the request for writing of the second key, the cryptographic processing unit is configured to decrypt the second key by the master key stored in the master key storage region, and the key writing processing unit is configured to write the decrypted second key to the service key storage region.