A system and method are described for performing authentication on a computing device using a mobile device connected over an audio channel to the computing device, in scenarios where smart card authentication may have been traditionally used. An application executing on the computing device receives a request from a user, which request requires authentication of the user before being allowed by the application. An audio transmission containing encoded data including information authenticating the user is received at the computing device from the user's mobile device via a microphone. The audio transmission is decoded and the information authenticating the user is extracted. The information authenticating the user is verified and the request is allowed in the application.