Biometric authentication system and biometric authentication method

A biometric authentication system comprising:

• a server device implemented with a computer hardware, the server device being configured to store first biometric data of a plurality of users in a registering unit;
• a client device implemented with a computer hardware, the client device being configured to sample biometric data received from the users, the system being configured to authenticate the sampled biometric data by use of the first biometric data registered in the registering unit,
• the client device including a first processor and a first memory storing instructions that cause the first processor to execute:
• retaining second biometric data of the plurality of users together with user information in a retaining unit,
• verifying biometric data sampled from a user among the plurality of users with the second biometric data when in authentication,
• synthesizing information of the second biometric data of which verification is successful and the biometric data sampled from the user, and
• transmitting user information of biometric data of which the verification is successful and the synthesized information to the server device,
• the server device including a second processor and a second memory storing instructions that cause the second processor to execute:
• verifying biometric data specified by the user information sent from the client device in plural sets of the first biometric data registered in the registering unit with the synthesized information sent from the client device,
• wherein the second biometric data related to the synthesized information is retained in the retaining unit when the verification with the synthesized information by the server device is successful,
• wherein the first processor further executes:
• extracting information on feature points from the biometric data of the user,
• selecting match feature points getting matched under predetermined conditions with feature points contained in the second biometric data from the extracted feature points,
• determining whether or not the verification gets successful or unsuccessful by use of the information on the selected match feature points,
• organizing the information on the match feature points into the synthesized information,
• determining such a polygonal area as to embrace all the match feature points and to minimize an area on the basis of the match feature point information, and
• calculating, as a match rate, a rate of the match feature points to all the feature points embraced in the polygonal area,
• wherein the first processor executes, if the calculated match rate exceeds a predetermined threshold value, determining that the verification becomes successful,
• wherein the second processor further executes:
• storing a history of the match rates together with time information with respect to each user;
• calculating a variation quantity of the match rate on the basis of the stored match rate history and the stored time information and monitoring that the variation quantity of the match rate reaches a predetermined decrease status;
• and
• notifying the client device that the match rate variation quantity about the user whose biometric data is authenticated reaches the predetermined decrease status, and
• the first processor further executes updating, when the server device notifies the client device that the match rate variation quantity about the user reaches the predetermined decrease status, the second biometric data with the biometric data sampled from the user.