CAPTCHA-Based DDoS Defense System of Call Centers Against Zombie Smart-Phone
Recently, some researchers alarm the security community that the smart-phone which is interoperable between telecom networks and Internet, is dangerous conduits for Internet security threats to reach the telecom network such as DDoS attacks to the emergency call center. But the detailed DDoS defense scheme for the emergency call center against DDoS attack by zombie smart-phones is not presented yet. This paper presents a DDoS defense system, called cushion system, against zombie smart-phones to protect the emergency call center such as 911. The cushion system, a Private Branch eXchange(PBX) extension, differentiates the legitimate human users and zombie smart-phones using CAPTCHA test which can be solved by only human users.