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

1. A data protection method for a data protection system which includes a device, a plurality of authentication servers, and a plurality of data servers, the data protection method being performed by a first authentication server included in the plurality of authentication servers, and comprising:

obtaining identification information and a third hash value from the device, the identification information identifying first encrypted history information of first history information which is targeted for data verification, the third hash value being obtained from the first history information;

generating first transaction data which includes the identification information and indicates a data verification request, and transmitting the first transaction data to the at least one of the plurality of data servers;

obtaining, from the at least one of the plurality of data servers, a fourth hash value computed by the at least one of the plurality of data servers performing computation processing on the first encrypted history information without decrypting the first encrypted history information, the first encrypted history information being identified by the identification information from among one or more items of 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;

determining whether the third hash value and the fourth hash value match; and

when the third hash value and the fourth hash value do not match, generating second transaction data which includes the identification information and indicates a deletion request for deletion of the first encrypted history information identified by the identification information, and transmitting the second transaction data to the at least one of the plurality of data servers.

2. The data protection method according to claim 1 , further comprising:

when the third hash value and the fourth hash value do not match, recording the second transaction data in the distributed ledger in synchronization with the plurality of authentication servers excluding the first authentication server.

3. The data protection method according to claim 1 , wherein the history information includes personal data of a user of the device.

4. The data protection method according to claim 1 , further comprising:

receiving transaction data which is generated by the device and includes a first hash value obtained from history information of the device;

obtaining, 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;

verifying the transaction data, and determining whether the first hash value and the second hash value match; and

when a validity of the transaction data is verified and the first hash value and the second hash value match, recording the transaction data in a distributed ledger in synchronization with the plurality of authentication servers excluding the first authentication server.

5. A computer comprising:

a processor; and

a memory that stores a program for causing the processor to execute the method according to claim 1 .

6. A non-transitory storage medium storing a program that causes a processor to execute the method according to claim 1 .