Γράψτε μια εφαρμογή Android -- 2

Android text messages and file exchange In this project you have to create a message and file transfer/exchange application. This is a simplified chat application with security in mind. This infrastructure is composed of a central server and multiple users who exchange messages with each other via the server. The service will be framed by users and authentication procedures agreement cryptographic keys to ensure the communication of end users. Implementation For the implementation of the application must deploy applications in JAVA and Android. Essentially you need to develop an application for the server service and one for the client. The first, need not be based on a graphical interface. For the client implementation you should develop appropriate GUI for servicing the infrastructure functions on Android. Server We assume that the Server holds a pair of public and private key (RSA -1024bits). It should maintain a data base of available users and to disclose to customers when necessary. Moreover, the base will reserve the public encryption keys of each user connected to the infrastructure. Communication with customers based on SOCKETS. Client The Client should develop appropriate GUI, that supports the functions of messaging and file transfer. The Client each time boots, generates a pair of public and private key (RSA - 1024bits). Communication protocols: Users authentication For authentication of users on the server must implement the following protocol. The process results in the creation of a session key to secure communication between server-client. Key agreement scenario In this scenario key role is played by a central server. When the user A wants to communicate with the user B, initially sends the corresponding request to the server (Step 1). Then the server generates an AES-128 symmetric encryption key and delivers it to the two participants, which is encrypted with their public keys. First, the symmetric key is delivered to B and after receiving confirmation (ACK) from him, the server delivers to A (and expects to confirm). Not taking confirmation causes resending the key from the server. Then both users can this key to encrypt messages and files. Wanted: • Server application on JAVA. • Client application on Android. • The communication protocol between entities – Each entity will have a separate class in your code. • The communications will be based on sockets. • Is communication protocol safe? If not, what would you propose to further secure the protocol? • Verify that the messages exchanged will be in encrypted form. • Conclusions. Optional - Output message integrity assurance mechanism.