Biometric authentication system, authentication client terminal, and biometric authentication method

A biometric authentication system comprising:

• a database holding enrolled feature data with respect to each of enrolled users un (n=1 to N);
• a feature extraction unit for extracting feature data of a claimant v based on biometric data acquired from the claimant v;
• a 1:N matching unit for performing 1:N matching between the extracted feature data of the claimant and the feature data held in the database, and calculating a matching score of each of the enrolled users un;
• a likelihood ratio calculation unit for calculating a ratio of the likelihood v=un to the likelihood v≠un with respect to each of the enrolled users un, using the calculated matching scores;
• and
• a determination unit for comparing each of the likelihood ratios with a first threshold, when a maximum value of the likelihood ratio is larger than the first threshold, the determination unit determining that the enrolled user corresponding to the likelihood ratio showing the maximum value is identical to the claimant v, while when the maximum value of the likelihood ratio is equal to or less than the first threshold, and when the number of acquisitions of the biometric data from the claimant v is less than a predetermined value, the determination unit requesting to reacquire the biometric data of the claimant v, and when the number of acquisitions is equal to or more than the predetermined value, the determination unit determining “authentication failure”.

An authentication client terminal capable of communicating with an authentication server terminal, the authentication server terminal including a database holding enrolled feature data with respect to each of enrolled users un (n=1 to N), and a prior probability setting unit for setting prior probabilities of the enrolled users un and a prior probability of a non-enrolled user u0,

• the authentication client terminal comprising:
• a feature extraction unit for extracting the feature data of a claimant v based on the biometric data acquired from the claimant v;
• an authentication request unit for transmitting the extracted feature data of the claimant to the authentication server terminal, calculating a ratio of likelihood v=un to likelihood v≠un with respect to each of the enrolled users un, based on the feature data of the claimant and the matching feature data held in the database, calculating the posterior probabilities of the enrolled users un and the posterior probability of the non-enrolled user u0, using the calculated likelihood ratios, the prior probabilities of the enrolled users un, and the prior probability of the non-enrolled user u0, comparing each of the calculated posterior probabilities with a first threshold, when a maximum value of the posterior probability is larger than the first threshold, the authentication request unit requesting to transmit the information of the enrolled user un or non-enrolled user u0 corresponding to the posterior probability showing the maximum value, and acquiring the information transmitted from the authentication server terminal in response to the request;
• and
• a determination unit for determining that when the acquired information is of the enrolled users un, the enrolled user un and the claimant v are identical, and that when the acquired information is of the non-enrolled user u0, the claimant v is a user other than the enrolled users un.

A biometric authentication method comprising:

• a step of extracting feature data of a claimant v based on the biometric data acquired from the claimant v;
• a prior probability setting unit for setting prior probabilities of the enrolled users un and a prior probability of a non-enrolled user u0;
• a step of calculating a ratio of likelihood v=un to likelihood v≠un with respect to each of the enrolled users un, based on the feature data held in the database with respect to each of the enrolled users un (n=1 to N), as well as on the extracted claimant feature data;
• a step of calculating posterior probabilities of the enrolled users un and a posterior probability of the non-enrolled user u0, using the calculated likelihood ratios, the prior probabilities of the enrolled users un, and the prior probability of the non-enrolled user u0;
• and
• a step of comparing each of the calculated posterior probabilities with a first threshold, when a maximum value of the posterior probability is larger than the first threshold, and when the posterior probability showing the maximum value is one of the posterior probabilities of the enrolled users un, determining that the corresponding enrolled user and the claimant v are identical, while when the posterior probability showing the maximum value is the posterior probability of the non-enrolled user u0, determining that the claimant v is a non-enrolled users u0.