Authors

• Mariam T. Sulaiman ¹
• Nidaa F. Hassan ²

¹ Computer Science Department University of Technology, Baghdad, Iraq

² Computer Science, Department, University of Technology, Baghdad, Iraq.

Abstract

CAPTCHA is the facility that prevents web bots from accessing
the web services by generating tests to check whether the user is human or
computer program. In this paper, a new pseudo-random bits generator based
on chaotic system is offered to generate Arabic letters and numbers for
CAPTCHA system. The proposed generator uses two Jacobian elliptic
Chebyshev rational maps that are combined in the algorithm to produce a
block of 32bits in each iteration. A specified number of bits are selected from
the resulted blocks to be converted to a set of Arabic letters and numbers.
National Institute of Standards and Technology (NIST) statistical test suite
are used to assess the generator randomness, all tests has been passed except
Longest Run of Ones in a Block Test, Binary Matrix Rank Test and Random
Excursions Test.

Keywords

• CAPTCHA
• chaotic map
• Jacobian elliptic Chebyshev rational map
• NIST statistical test suite
• pseudo-random bits generator

Main Subjects

• Science