A New Secure and Usable Captcha-Based Graphical Password Scheme

CaRP are known graphical password schemes using Captcha visual objects for password setting. CaRP contains four schemes with different alphabet symbols used for password specification. We generalize CaRP schemes introducing Click Symbol-Alphanumeric (CS-A) scheme which as CaRP schemes, ClickText (CT), ClickAnimal (CA), AnimalGrid (AG), and ClickPoint (CP), uses a proper symbol selection on the screen by clicking, but does not specify a particular alphabet. In particular, we show that using together in one alphabet Alphanumeric (A) and Visual (V) symbols (CS-AV) improves its usability and users are more motivated towards making strong passwords. For the security analysis, we applied segmentation techniques to identify the symbols on CT and proposed CS-AV. The segmentation and symbols identification of CS-AV and CT scheme do not reveal sensitive information. This paper also studies the usability: Experiments on both schemes show that such usability feature as memorability of CS-AV is greater by 3.75% than that of CT scheme.