Abstract: Network Security is a specialized field in computer science that involves securing a network infrastructure. Denial-of-service (DoS) and distributed DoS (DDoS) are the major threats to cyber-security. In computing, a denial-of-service (DoS) attack is an attempt to make network resource unavailable to its intended users. DDos is short for Distributed Denial of Service. DDoS is a type of DOS attack where multiple systems, which are often infected with a Trojan, are used to target a single system causing a Denial of Service (DoS) attack. To prevent the Denial-of-service and distributed DoS attack a client puzzle method is implemented. In order to prevent further attack in network and to enhance the security the request that is provided by the client and the file sent by the server to client is in encrypted form. One drawback of existing system is if the attacker identifies the port, he can intrude or interfere in the communication and flood DOS attack and can hack communicating data. The methodology used is explained as follows. First the client has to solve a puzzle generated by the server. Then the client checks the latency of the file that has to be accessed from server database. The client can test the latency of the server by inputting the corresponding server IP address, number of packets, and the length of data in bytes. After processing the latency checking parameters, ping statistics of the server and the approximate round trip time will be displayed in the result. The client then encrypts the request and sends the request to server. AES Algorithm is used to perform the encryption and decryption. The server upon receiving the request has to decrypt the request using the client port number and IP address. The server sends the requested file by encrypting the file. Finally the client receives the file, decrypts the content and read it. Thus it can be concluded that more reliable communication can be performed between server and clients and active communications remains unaffected even in the presence of DDoS attacks. This scheme is mainly used for military applications.
Keywords: Denial of service (Dos) Attack, Distributed Denial of service (DDos) attack, Software Puzzle, AES algorithm.