mobile computing

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Introduction
Mobile computing has been given special attention as the next personal computing and communication environment, because of the enormous improvement in performance of the portable computer, personal digital assistant (PDA), and wireless networking infrastructure. However, mobile communication infrastructures, especially wireless data networks, lack communication speed, reliability and security. Mobile users are worried about information leakage by wireless tapping. Therefore, research and development is needed for communication security of mobile computing environments. Encryption tools and new applications that use exclusive API for security control have been proposed. This paper describes a communication method with data compression and encryption for mobile computing environments. This method offers communication, data compression and encryption from end to end by adding a process via WinSock API without changing the existing TCP/IP-based application.
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Problems of communication, data compression and encryption processing
There are two methods of compressing and encrypting communication data:
<!--[if !supportLists]-->1. <!--[endif]-->Encryption done by the application and compression done by the modem.
<!--[if !supportLists]-->2. <!--[endif]-->Embedding the functions of encryption and compression into the communication control software.
Both methods have problems. High-performance compression is not anticipated using method 1, because data randomizing by the first encryption process removes regularity, thereby preventing efficient compression in the compression sequence after the encryption sequence. Applications should have the encrypting function in the case of method 1. There is another problem: In method 2, changing the TCP/IP software is necessary, which is against our goal. The method of data compression and encryption processing in PPP (Point to Point Protocol) is popular, but it only takes effect between client and access server.
Data compression and encryption by intercepting WinSock command from WinSock API
WinSock API is a standard application programming interface for TCP/IP-based PC communication programs. We achieved embedded data compression and encryption without changing the TCP/IP and application software by intercepting WinSock commands from WinSock API temporarily and adding individual processing. Figure 2 shows intercepting WinSock commands.
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First, our application execution support program changes the linkage between the target application program and WinSock DLL program when the target application program is loaded into memory by the loader before its execution. The secure communication add-in program that we developed intercepts the send command of the application program from WinSock API, compresses its data in the send command, encrypts the data, and then returns this command to WinSock DLL, which is properly transferred. On the other hand, the receive command is intercepted from WinSock API, as with the send command. Also, the secure communication add-in program decrypts the data received from WinSock DLL, decompresses it, and then returns it to the application program, which is properly transferred. Other commands of WinSock are processed in the same way as above. By using this method, we have achieved these features without changing any program or any interfaces.