关键词: 图形验证码, 网络攻击, Web安全

Abstract: The current CAPTCHA is so simple that it can be easily identified by the automated procedures, which may cause many security risks. On the purpose of enhancing the security of Web applications, an improved CAPTCHA algorithm based on the random sequence was introduced. First of all, the algorithm created a true color image with random background color. Second, it determined characters and the number of character that were randomly generated in a certain range. Finally, the algorithm put characters on the image and the positions of characters were random. To determine the sequence of characters, lines were put between characters. The characteristic of the algorithm is that the number, font, position and input sequence of the characters were uncertain. The experimental results show that the CAPTCHA based on random sequence has great advantages, which can provide a strong security for Web applications.

Key words: CAPTCHA, network attack, Web security