Abstract
ABSTRACTAs one of the effective access control mechanism, CAPTCHA can provide privacy protection and multimedia security for big data. In this paper, an attack on hollow CAPTCHA using accurate filling and nonredundant merging is proposed. Firstly, a thinning operation is introduced to repair character contour precisely. Secondly, an inner-outer contour filling algorithm is presented to acquire solid characters, which only fills the hollow character components rather than noise blocks. Thirdly, the segmentation to the solid characters produces mostly individual characters and only a small number of character components. Fourthly, a minimum-nearest neighbor merging algorithm is proposed to obtain individual characters without redundancy. Lastly, the convolutional neural network (CNN) is applied to acquire the final recognition results. The experimental results based on the real CAPTCHA data sets show that comparing with the existing attack methods on hollow CAPTCHA, the proposed method has higher success rate and superior efficiency.
Highlights
With the proliferation of network, huge amounts of data are being explosively generated every day
We propose an attack on hollow CAPTCHA using accurate filling and nonredundant merging (AF& NM)
In order to solve the above problems, this paper proposes an attack on hollow CAPTCHA using accurate filling and nonredundant merging
Summary
With the proliferation of network, huge amounts of data are being explosively generated every day. How to protect the security and privacy for big data becomes a key issue in this field. As one of the effective access control mechanisms, CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart [1]) is widely applied to many large websites, including Google, Yandex, and so on. CAPTCHA has played an increasingly important role in privacy protection and multimedia security for big data. The frequently used CAPTCHAs are textbased CAPTCHA, image-based CAPTCHA, shortmessage-service -based CAPTCHA, audio-based CAPTCHA, etc. The most widely-used CAPTCHA is the text-based schemes [2], an image containing several distorted characters. The typical types of text-based CAPTCHA are solid CAPTCHA, hollow CAPTCHA, 3D CAPTCHA, etc
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