A New Text Based CAPTCHA
Eric Ke Wang, Yun Ming Ye · Applied Mechanics and Materials · 2013
Attacks on text-based CAPTCHAs are getting more sophisticated. Most existing schemes defend attacks by increasing deformation or distortion rate of words which sacrifice the friendliness of the system. In this paper, we propose a secure one time text-based CAPTCHA scheme which can effectively defend multiple attacks without decreasing the friendliness of the scheme for valid users. The core of our design is an information obfuscation scheme which determines which character image to display and which to hide in an online manner from a sequence of 62 character images which makes it more difficult to attack. Encryption method is employed for protecting display policies which control showing and hiding of information. Prototype has been implemented and the preliminary results are encouraging.