A biometric authentication system including a user terminal and an authentication server which is connected with the user terminal across a network , wherein: the user terminal comprises: a sensor adapted to acquire biometric information of a user; a feature extraction unit adapted to extract feature data for authentication from the acquired biometric information; a feature data encoding unit adapted to encode the feature data for authentication, thus creating encoded feature data for authentication; and a transmitting unit adapted to transmit identification request information including the encoded feature data for authentication to the authentication server, and the authentication server comprises: a DB for storing biometric encrypted authentication information; a search unit adapted to search for biometric encrypted authentication information included in the DB, based on the identification request information; a decryption processing unit adapted to decrypt the biometric encrypted authentication information searched out using the encoded feature data for authentication as a decryption key and to uniquely identify a user, based on authentication information obtained by the decryption; and an authentication response processing unit adapted to perform authentication response processing with respect to the identified user, based on the authentication information obtained by decryption, on behalf of the user terminal. the user terminal comprises: a sensor adapted to acquire biometric information of a user; a feature extraction unit adapted to extract feature data for authentication from the acquired biometric information; a feature data encoding unit adapted to encode the feature data for authentication, thus creating encoded feature data for authentication; and a transmitting unit adapted to transmit identification request information including the encoded feature data for authentication to the authentication server, and a sensor adapted to acquire biometric information of a user; a feature extraction unit adapted to extract feature data for authentication from the acquired biometric information; a feature data encoding unit adapted to encode the feature data for authentication, thus creating encoded feature data for authentication; and a transmitting unit adapted to transmit identification request information including the encoded feature data for authentication to the authentication server, and the authentication server comprises: a DB for storing biometric encrypted authentication information; a search unit adapted to search for biometric encrypted authentication information included in the DB, based on the identification request information; a decryption processing unit adapted to decrypt the biometric encrypted authentication information searched out using the encoded feature data for authentication as a decryption key and to uniquely identify a user, based on authentication information obtained by the decryption; and an authentication response processing unit adapted to perform authentication response processing with respect to the identified user, based on the authentication information obtained by decryption, on behalf of the user terminal. a DB for storing biometric encrypted authentication information; a search unit adapted to search for biometric encrypted authentication information included in the DB, based on the identification request information; a decryption processing unit adapted to decrypt the biometric encrypted authentication information searched out using the encoded feature data for authentication as a decryption key and to uniquely identify a user, based on authentication information obtained by the decryption; and an authentication response processing unit adapted to perform authentication response processing with respect to the identified user, based on the authentication information obtained by decryption, on behalf of the user terminal. <EOS>