Digital Image Chaotic Encryption And Transmission System Based On FTP

The development of mobile operating systems and progress of low-power chip manufacturing technique have made mobile equipment popular, such as smartphone and tablet PC, which have changed way of work and entertainment for most people. With the popularity of mobile net-surfing and mobile payment, security issues on embedded equipment have been paid more attention than ever. Because of its visual characteristics, digital image has taken place of short message, which once was the most popular way of transferring information on mobile phones. Thus, the solution of how to transmitting digital image safely on embedded equipment becomes one of the most popular research areas. Most ordinary encryption methods are designed for text, which are not efficient ways of image encryption. However, researches on chaotic phenomenon indicate that chaotic systems are more suitable for encrypting digital image than ordinary encryption methods.In order to solve the problem of safely transmitting digital images on embedded equipment, this paper has designed a chaotic encrypting and transmitting system based on File Transfer Protocol. This system includes two parts as showed below:1. Chaotic sequence encryption algorithm designed for bitmap image. Based on the analysis of researches on this issue at home and abroad, this paper proposes a sequence encryption algorithm to encrypt digital images, which is realized by using chaotic sequence. A disturbing policy and a diffusion mechanism are mixed into encryption scheme, which is to make sure that the chaotic scheme be strong enough when confronting key-exhaustive attack or choose/known plain-text type of attack. Output values of disturbing system are used to operating with plain-text image data. The results are used as key sequence, which makes sure that the chaotic encryption sequence not only depend on chaotic system, but also rely on specific plain-text image. Because bitmap image is incompressible, which makes bitmap be able to retain characteristics of image, the encryption algorithm is just designed for bitmap image for now.2. A secure FTP server based on vsftpd. The transmitting system is realized on ARM development board. The FTP server is built on the embedded Linux platform with vsftpd, which is used to transmit encrypted image files through network. The FTP server provides support for SSL/TLS protocol and management of users’access privilege to keep both plain-text image and encrypted image safe on the server, which also makes sure that encrypted images are safely transmitted.The transmitting process is as described below:after the plain-text image has been encrypted on the server, the encrypted image file is moved to home folder of FTP user. The client then logs in with users’name and password, and receives the encrypted image from server, which is decrypted on the client. Result of test indicates that this system can transmit the digital image safely and quickly, and it is strong enough to defend choose/known plain-text and exhaustive attacks. The FTP server is safe under complicated network environments. Result of this paper has promoted the application of chaotic systems.