With the rapid development of the Internet the widespread popularization of communication technology,the file forwarding volume is increasing day by day,which makes the security and privacy of files urgently need a simple and convenient function to protect them. If access to file permission can be controlled, the functions of chat software will be richer and safer. In the design process, we are faced with two major challenges:(1)If an object is specified, only this object can receive the information sent by users;(2)It must be sure that users have forwarding permission when forwarding files and this permission can only be determined by the sender and must be secure. To solve the above problems, we adopt C/S structure, which is divided into server-side and client-side to develop software. We build the server-side to help the client by connecting to the back-end databases, such as user login verification, realization of chat software, file permission access control, etc. The we build the client-side to realize the entry of account passwords and messages, the receipt of messages, etc. Furthermore, we proved that the security of this software and it not need to encrypt the files, which is efficient and convenient.