Cryptology ePrint Archive: Report 2010/478

Cryptanalysis of the Convex Hull Click Human Identification Protocol

Hassan Jameel Asghar and Shujun Li and Josef Pieprzyk and Huaxiong Wang

Abstract: Recently a convex hull based human identification protocol was proposed by Sobrado and Birget, whose steps can be performed by humans without additional aid. The main part of the protocol involves the user mentally forming a convex hull of secret icons in a set of graphical icons and then clicking randomly within this convex hull. While some rudimentary security issues of this protocol have been discussed, a comprehensive security analysis has been lacking. In this paper we analyse the security of this convex hull based protocol. In particular, we show two probabilistic attacks which reveal the user's secret after the observation of only a handful of authentication sessions. These attacks can be efficiently implemented as their time and space complexities are considerably less than brute force attack. We show that while the first attack can be mitigated through appropriately chosen values of system parameters, the second attack succeeds with a non-negligible probability even with large system parameter values which cross the threshold of usability.

Category / Keywords: cryptographic protocols / Human Identification Protocols, Observer Attack, Entity Authentication

Publication Info: A short paper with the same title is to appear in the proceedings of the Information Security Conference (ISC) 2010. This is the full version of the paper.

Date: received 10 Sep 2010

Contact author: hassan jameel at gmail com

Available format(s): PDF | BibTeX Citation

Version: 20100912:162810 (All versions of this report)

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