In the thesis we focus on designing an authentication system to authenticate users over a network with a username and a password. The system uses the zero-knowledge proof (ZKP) system as a password verification mechanism. The ZKP protocol used is based on the quadratic residuosity problem. The authentication system is defined as a method in the extensible authentication protocol (EAP). Using a ZKP system yields interesting security properties that make the system favourable to be used over insecure networks.