A method for biometric authentication of a user of a mobile device, and a case for performing the method is provided. The method includes, by the case, coupling the mobile device to the case, receiving from the mobile device biometric data of the user of the mobile device that was captured by the mobile device, storing the biometric data, receiving a request from the mobile device for authenticating the user of the mobile device, the request including biometric data captured by the mobile device, comparing the biometric data stored in the case and the biometric data included in the request, and sending to the mobile device a response to the request for authenticating the user of the mobile device based on a result of the comparison, wherein the response to the request is for use by the mobile device to perform an operation based on the authentication of the user.