A system and method for authentication are provided. The system for authentication according to one embodiment of the present disclosure includes: a service server configured to: receive a first authentication request message from an authentication server and convert a random number included in the first authentication request message into an optical code; a first user terminal configured to receive the optical code from the service server and display the optical code; and a second user terminal configured to: recognize the random number by capturing an image of the displayed optical code in response to receiving a second authentication request message from the service server and authenticate a user by using the random number, the second authentication request message, and biometric information of the user.