a simple generic attack on text captchas
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A Simple Generic Attack on Text Captchas Haichang Gao (Xidian - PowerPoint PPT Presentation

A Simple Generic Attack on Text Captchas Haichang Gao (Xidian University), Jeff Yan (Lancaster University), Fang Cao, Zhengya Zhang, Lei Lei, Mengyun Tang, Ping Zhang, Xin Zhou, Xuqin Wang and Jiawei Li (Xidian University) Introduction CAPTCHA :


  1. A Simple Generic Attack on Text Captchas Haichang Gao (Xidian University), Jeff Yan (Lancaster University), Fang Cao, Zhengya Zhang, Lei Lei, Mengyun Tang, Ping Zhang, Xin Zhou, Xuqin Wang and Jiawei Li (Xidian University)

  2. Introduction CAPTCHA : Completely Automated Public Turing Test to Tell Computers and Humans Apart .

  3. Gabor Filters Dennis Gabor laid their theoretical foundations in 1946. The temporal (1-D) Gabor filters The Spatial (2-D) Gabor filters Log-Gabor filters 2D Log-Gabor filters

  4. Real World Popular Captchas

  5. Our Attack

  6. Our Attack : Extracting Components

  7. Our Attack : Extracting Components

  8. Our Attack : Partition and Recognition Step 1. Component sorting

  9. Our Attack : Partition and Recognition Step 2. Graph building

  10. Our Attack : Partition and Recognition Step 2. Graph building

  11. Our Attack : Partition and Recognition Step 3. Graph pruning

  12. Our Attack : Partition and Recognition Step 3. Graph pruning

  13. Our Attack : Partition and Recognition Step 4. Recognizing component combinations

  14. Our Attack : Partition and Recognition Step 4. Recognizing component combinations

  15. Our Attack : Partition and Recognition Step 5. Graph search

  16. Evaluation : Attack Results

  17. Evaluation : Further Applicability Test

  18. Evaluation : A Comparison with Prior Art pixel counting, histogram analysis, CFS Decaptcha : preprocessing, segmentation, post-segmentation, recognition, and post-preprocessing CCS’13: The Robustness of Hollow Captchas. WOOT’ 14:The End is Nigh: Generic Solving of Text-based Captchas .

  19. Design Choices : Graph Search Algorithms

  20. Design Choices : Extraction Orientations

  21. Design Choices : Extraction Orientations

  22. Design Choices : Extracting Methods

  23. Design Choices : Classifiers

  24. Defence

  25. Summary and Conclusion

  26. Thank you !

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