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

• US 20090289760A1
• Filed: 02/27/2009
• Published: 11/26/2009
• Est. Priority Date: 04/30/2008
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Takahashi, Kenta, Murakami, Takao
• Granted Patent: US 8,340,361 B2
• Time in Patent Office: Days
• US Class Current: 340/5.820
• CPC Class Codes: G06F 18/2415 based on parametric or probabilistic models, e.g. based on likelihood ratio or false acceptance rate versus a false rejection rate
• CPC Class Codes: G06V 40/10 Human or animal bodies, e.g. vehicle occupants or pedestrians; Body parts, e.g. hands
• CPC Class Codes: G06V 40/70 Multimodal biometrics, e.g. combining information from different biometric modalities

Abstract

A biometric authentication system, authentication client terminal, and biometric authentication method are provided to reduce an expected value of the number of inputs of biometric data for authentication, while effectively preventing forgery. In a biometric authentication system, prior probabilities of enrolled users u_n and non-enrolled user u₀ are previously set. 1:N matching is performed between feature data of a claimant v and matching feature data. The matching score is calculated for each enrolled user u_n. A ratio of the likelihood v=u_n to the likelihood v≠u_n is calculated for each enrolled user u_n using the calculated matching scores. Posterior probabilities of the enrolled users u_n and non-enrolled user u₀ are calculated, using the likelihood ratios, and the prior probabilities of both the enrolled users u_n and the non-enrolled user u₀. Then, determination is made by comparing each posterior probability with a first threshold.

Claims

1. A biometric authentication system comprising:

a database holding enrolled feature data with respect to each of enrolled users u_n (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 prior probability setting unit for setting prior probabilities of the enrolled users u_n and a prior probability of a non-enrolled user u₀;

a likelihood ratio calculation unit for calculating a ratio of the likelihood V=u_n to the likelihood v≠

u_n with respect to each of the enrolled users u_n, based on the enrolled feature data held in the database and the extracted claimant feature data of the claimant;

a posterior probability calculation unit for calculating posterior probabilities of the enrolled users u_n and a posterior probability of the non-enrolled user u₀, using the calculated likelihood ratios, the prior probabilities of the enrolled users u_n, and the prior probability of the non-enrolled user u₀; and

a determination unit for 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 u_n, the determination unit 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, the determination unit determining that the claimant v is a non-enrolled user u₀.

2. The biometric authentication system according to claim 1, further comprising a 1:

N matching unit for performing 1;

N matching between the extracted claimant feature data of the claimant and the enrolled feature data held in the database, and calculating a matching score of each of the enrolled users u_n,

wherein the likelihood ratio calculation unit calculates the likelihood ratio of each of the enrolled users u_n by using the calculated matching scores.

3. The biometric authentication system according to claim 1,

wherein, when the maximum value of the posterior probability 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 requests to reacquire the biometric data of the claimant v, while when the number of acquisitions is equal to or more than the predetermined value, the determination unit determines “

authentication failure”

.

4. The biometric authentication system according to claim 3, further comprising an enrolled user pruning unit,

wherein, when the determination unit requests to reacquire the biometric data from the claimant v, the enrolled user pruning unit compares each of the posterior probabilities calculated by the posterior calculation unit with a second threshold, and excludes an enrolled user u_n corresponding to the posterior probability smaller than the second threshold, from the target to be matched to the claimant v.

5. The biometric authentication system according to claim 3,

wherein the posterior probability calculation unit compares the posterior probability of the non-enrolled user u₀ calculated in the current acquisition of the biometric data from the claimant v with the prior probability of the non-enrolled user u₀ when the number of acquisitions is one, or with the posterior probability of the non-enrolled user u₀ calculated in the previous acquisition of the biometric data when the number of acquisitions is two or more, and

wherein, when the posterior probability of the non-enrolled user u₀ calculated in the current acquisition is higher, the posterior probability calculation unit does not use the feature data extracted in the current acquisition in the calculation of posterior probabilities in the subsequent acquisitions of the biometric data from the claimant v.

6. The biometric authentication system according to claim 3,

wherein the database holds a plurality of different types of feature data belonging to a plurality of modalities with respect to each of the users u_n, and

wherein the biometric authentication system further comprises a biometric information input sensor that allows for acquisition of the biometric data only once with respect to each of modalities.

7. The biometric authentication system according to claim 3,

wherein the database holds a plurality of different types of feature data belonging to the same modality with respect to each of the enrolled users u_n, and

wherein the 1:

N matching unit determines “

authentication failure”

when the best matching score is obtained several times for the same biometric information until acquisition of the biometric data in this time.

8. The biometric authentication system according to claim 3,

wherein the database holds a plurality of different types of feature data belonging to the same modality with respect to each of the enrolled users u_n, and

wherein, when the best matching score is obtained several times for the same biometric information until acquisition of the biometric information in this time, the 1:

N matching unit does not use among the matching score above the matching scores calculated in acquisitions other than the acquisition with the best matching score for the calculation of likelihood ratios by the likelihood ratio calculation unit.

9. The biometric authentication system according to claim 1,

wherein, when the determination unit determines that the claimant v is a non-enrolled users u₀, the prior probability setting unit increases the prior probabilities of the non-enrolled users u₀.

10. The biometric authentication system according to claim 1,

wherein the first threshold is larger than 0.5.

11. The biometric authentication system according to claim 1,

wherein the determination unit outputs forgery warning information about the forgery when it is determined that the claimant v is the non-enrolled users u₀.

12. The biometric authentication system according to claim 1, further comprising:

a loss calculation unit; and

a prior probability and threshold setting unit,

wherein, each time authentication is performed, the loss calculation unit calculates a loss W₁ when the claimant v is an enrolled user and is identified as another enrolled user, and a loss W₀ when the claimant v is a non-enrolled user and is identified as a certain enrolled user, and

wherein the prior probability and threshold setting unit sets the prior probabilities of the enrolled users u_n and a corresponding threshold, as well as the prior probability of the non-enrolled user u₀ and a corresponding threshold, using the losses W₁ and W₀, respectively, so that EFRR as well as an expected value R_n of the loss when the claimant v is identified as the n-th enrolled user are equal to or less than respective desired values.

13. A biometric authentication system comprising:

a database holding enrolled feature data with respect to each of enrolled users u_n (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 u_n;

a likelihood ratio calculation unit for calculating a ratio of the likelihood v=u_n to the likelihood v≠

u_n with respect to each of the enrolled users u_n, 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”

.

14. The biometric authentication system according to claim 13, further comprising an enrolled user pruning unit,

wherein, when the determination unit requests to reacquire the biometric data, the enrolled user pruning unit compares each of the likelihood ratios calculated by the likelihood ratio unit with a second threshold, and excludes an enrolled user u_n corresponding to the likelihood ratio smaller than the second threshold, from the target to be matched to the claimant v.

15. 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 u_n (n=1 to N), and a prior probability setting unit for setting prior probabilities of the enrolled users u_n 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=u_n to likelihood v≠

u_n with respect to each of the enrolled users u_n, 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 u_n and the posterior probability of the non-enrolled user u₀, using the calculated likelihood ratios, the prior probabilities of the enrolled users u_n, 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 u_n 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 u_n, the enrolled user u_n 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 u_n.

16. The authentication client terminal according to claim 15,

wherein the authentication request unit requests to perform 1:

N matching between the extracted feature data of the claimant and the feature data held in the database, calculates the matching score of each of the enrolled users u_n, and calculates the likelihood ratio of each of the enrolled users u_n by using the calculated matching scores.

17. 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 u_n and a prior probability of a non-enrolled user u₀;

a step of calculating a ratio of likelihood v=u_n to likelihood v≠

u_n with respect to each of the enrolled users u_n, based on the feature data held in the database with respect to each of the enrolled users u_n (n=1 to N), as well as on the extracted claimant feature data;

a step of calculating posterior probabilities of the enrolled users u_n and a posterior probability of the non-enrolled user u₀, using the calculated likelihood ratios, the prior probabilities of the enrolled users u_n, 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 u_n, 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.

18. The biometric authentication method according to claim 17, further comprising a matching step of 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 u_n,

wherein the likelihood calculation step involves calculating the likelihood ratio of each of the enrolled users u_n by using the calculated matching scores.