Data protection method, authentication server, data protection system, and data structure

An authentication server in a data protection system which includes a device, a plurality of authentication servers including the authentication server, and a plurality of data servers, the authentication server comprising:

• a communication unit configured to receive transaction data which is generated by the device and includes a first hash value obtained from history information of the device, and obtain, from at least one of the plurality of data servers, a second hash value computed by the at least one of the plurality of data servers performing computation processing on encrypted history information without decrypting the encrypted history information, the encrypted history information being history information of the device encrypted using a secure computation method which enables computation without decrypting the encrypted history information, the encrypted history information being obtained from the device and recorded in the at least one of the plurality of data servers;
• a transaction data verifier which verifies the transaction data;
• a data verifier which determines whether the first hash value and the second hash value match;
• and
• a recorder which records the transaction data in a distributed ledger in synchronization with the plurality of authentication servers excluding the authentication server, when a validity of the transaction data is verified and the first hash value and the second hash value match.

A data protection system, comprising:

• a device;
• a plurality of authentication servers;
• and
• a plurality of data servers, wherein
• the device includes:
• a transaction data generator which generates transaction data including a first hash value obtained from history information of the device, and transmits the transaction data to an authentication server included in the plurality of authentication servers;
• and
• a first secure computation calculator which generates encrypted history information by encrypting the history information using a secure computation method which enables computation without decrypting the encrypted history information, and transmits the encrypted history information to the plurality of data servers,
• each of the plurality of data servers includes:
• a recorder which records the encrypted history information obtained from the device;
• and
• a second secure computation calculator which computes a second hash value of the recorded encrypted history information by performing computation processing on the recorded encrypted history information without decrypting the recorded encrypted history information, and transmits the second hash value to the authentication server, and
• the authentication server includes:
• a communication unit configured to receive the transaction data including the first hash value from the device, and obtain the second hash value from at least one of the plurality of data servers;
• a transaction data verifier which verifies the transaction data;
• a data verifier which determines whether the first hash value and the second hash value match;
• and
• a recorder which records the transaction data in a distributed ledger in synchronization with the plurality of authentication servers excluding the authentication server, when a validity of the transaction data is verified and the first hash value and the second hash value match.

A data structure used for a block recorded in a blockchain in a data protection system which includes a device, a plurality of authentication servers, and a plurality of data servers, the data structure comprising:

• a blockchain address which is an identifier for identifying a creator of transaction data included in the block of the blockchain;
• a transaction ID for identifying the transaction data;
• a first hash value which is included in the transaction data and obtained from history information of the device;
• and
• an electronic signature of a user of the transaction data, wherein
• the transaction data is included in the block when the first hash value and a second hash value match, the second hash value being computed by at least one of the plurality of data servers performing computation processing on encrypted history information without decrypting the encrypted history information, the encrypted history information being obtained from the device and being history information of the device encrypted using a secure computation method which enables computation without decrypting the encrypted history information.