New CAPTCHA Approach for Securing Online Social Network and Webpages Using Extended Finite Automata (XFA CAPTCHA)

Today computer and the internet play an
important role in our daily life. We have shown highly
remarkable of automated behavior that is criminal in
violation of terms of services such as auto sharing or send
friend request. SO, CAPTCHA is used for protecting
webpages against automated programs which are called
bots. It is providing challenge response tests that
determine whether or not the users are human or bot. It
contains various contorted letters that are difficult for
attacker’s bots, but easy for humans. Since there are a
lot of services on the internet, for example (email, social
network, search engine) which allow users to register,
during registration, some attackers write malicious
programs that make website resources damaged by
making automated software which is called (Bots). Many
research developed more techniques to prevent accessing
web resources by spammers. This paper introduces a
new mechanism of CAPTCHA approach using extended
finite automata (XFA) for securing web pages and online
social networks against a new breed of bots. The XFA
CAPTCHA is a CAPTCHA based on image which
generates its tests using the automata Graph technique.
The result of our research evidence that the mechanism
of XFA CAPTCHA is effective in terms of security and
usability respectively. As a result of that, it improved the
rate of efficiency by 97.8%, the time for solving is around
20 seconds, and the value the probability of success rate
for speculation attack is decreased to 1.03% in average.
When compared to other CAPTCHAs, the XFA
CAPTCHA is a strong competitor in terms of security
and usability function.