Abstract

CAPTCHAs are employed as a security measure to differentiate human users from bots. A new sound-based CAPTCHA is proposed in this paper, which exploits the gaps between human voice and synthetic voice rather than relays on the auditory perception of human. The user is required to read out a given sentence, which is selected randomly from a specified book. The generated audio file will be analyzed automatically to judge whether the user is a human or not. In this paper, the design of the new CAPTCHA, the analysis of the audio files, and the choice of the audio frame window function are described in detail. And also, some experiments are conducted to fix the critical threshold and the coefficients of three indicators to ensure the security. The proposed audio CAPTCHA is proved accessible to users. The user study has shown that the human success rate reaches approximately 97% and the pass rate of attack software using Microsoft SDK 5.1 is only 4%. The experiments also indicated that it could be solved by most human users in less than 14 seconds and the average time is only 7.8 seconds.

Highlights

  • With the expansion of Internet, a great many daily activities are done through Internet for convenience, including communication, education and e-commerce

  • A new audio CAPTCHA which exploits the gaps between human voice and synthetic voice rather than relays on the auditory perception of human is proposed to solve the previous questions

  • Unlike currently existed sound based CAPTCHAs, our CAPTCHA exploits the gaps between human voice and synthetic voice

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Summary

INTRODUCTION

With the expansion of Internet, a great many daily activities are done through Internet for convenience, including communication, education and e-commerce. Text-based CAPTCHAs relay on the distortion of digits/letters and other visual effects added in the background image. The user is asked to identify the distorted characters and entered them. The first ones present users with a sound clip which contains distorted numbers and characters with background noise. In contrast with the traditional sound based CAPTHCAs, our new proposed CAPTHCA exploits the gaps between human voice and synthetic voice. It generates challenges by presenting a sentence which is randomly selected from some books. The user is asked to read out the sentence, and the mechanism estimates weather it is a human or not by analyzing the generated audio file.

RELATED WORKS
THE PROPOSED SCHEME
THE ANALYSIS OF AUDIO FILE
The choice of the window function
The Indicators
The processes of the analysis
PARAMETERS DETERMINATION
RESULTS
USER STUDY
CONCLUSIONS
Full Text
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