Propose an Arabic CAPTCHA System based on Chaotic Maps

Abstract

CAPTCHA is the facility that prevents web bots from accessingthe web services by generating tests to check whether the user is human orcomputer program. In this paper, a new pseudo-random bits generator basedon chaotic system is offered to generate Arabic letters and numbers forCAPTCHA system. The proposed generator uses two Jacobian ellipticChebyshev rational maps that are combined in the algorithm to produce ablock of 32bits in each iteration. A specified number of bits are selected fromthe resulted blocks to be converted to a set of Arabic letters and numbers.National Institute of Standards and Technology (NIST) statistical test suiteare used to assess the generator randomness, all tests has been passed exceptLongest Run of Ones in a Block Test, Binary Matrix Rank Test and RandomExcursions Test.

Keywords

• captcha
• chaotic map
• jacobian elliptic chebyshev rational map
• nist statistical test suite
• pseudo-random bits generator