Final published version
Research output: Contribution in Book/Report/Proceedings - With ISBN/ISSN › Conference contribution/Paper › peer-review
Publication date | 11/2013 |
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Host publication | CCS '13 Proceedings of the 2013 ACM SIGSAC conference on Computer & communications security |
Place of Publication | New York |
Publisher | ACM |
Pages | 1075-1086 |
Number of pages | 12 |
ISBN (print) | 9781450324779 |
<mark>Original language</mark> | English |
Event | 2013 ACM SIGSAC Conference on Computer and Communications Security, CCS 2013 - Berlin, Germany Duration: 4/11/2013 → 8/11/2013 |
Conference | 2013 ACM SIGSAC Conference on Computer and Communications Security, CCS 2013 |
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Country/Territory | Germany |
City | Berlin |
Period | 4/11/13 → 8/11/13 |
Conference | 2013 ACM SIGSAC Conference on Computer and Communications Security, CCS 2013 |
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Country/Territory | Germany |
City | Berlin |
Period | 4/11/13 → 8/11/13 |
CAPTCHA is now a standard security technology for differentiating between computers and humans, and the most widely deployed schemes are text-based. While many text schemes have been broken, hollow CAPTCHAs have emerged as one of the latest designs, and they have been deployed by major companies such as Yahoo!, Tencent, Sina, China Mobile and Baidu. A main feature of such schemes is to use contour lines to form connected hollow characters with the aim of improving security and usability simultaneously, as it is hard for standard techniques to segment and recognize such connected characters, which are however easy to human eyes. In this paper, we provide the first analysis of hollow CAPTCHAs' robustness. We show that with a simple but novel attack, we can successfully break a whole family of hollow CAPTCHAs, including those deployed by all the major companies. While our attack casts serious doubt on the viability of current designs, we offer lessons and guidelines for designing better hollow CAPTCHAs.