Disclosed are a system for security authentication via a mobile device, which includes: a first terminal of a user which requests mobile authentication; a server which generates authentication information and a key for encryption, encrypts the authentication information with the key, and divides the key into first information and second information to transmit the first information to the first terminal and transmit the second information and the encrypted information to a second terminal of the user; and the second terminal which acquires the first information from the first terminal, generates the key based on the first information and the second information, and acquires the authentication information by using the generated key.