Abstract: Among other things, the present disclosure describes an authentication system that leverage a mobile phone to improve the security of web logins and web payments on a personal computer. The described embodiments do not require special hardware beyond a cell phone with a camera. Using embodiments of the present invention, memorization of passwords is avoided and the login process is faster and less error-prone than with existing systems. In a payment system according to an embodiment, users do not need to let retailers keep their passwords because credit card information need to be manually input. In addition, the present invention allows users to conveniently take advantage of one-time use credit cards for additional security.