Create a Client-Sever application that allows for the sending and receiving of signed encrypted messages

• Create an application that generates public-private key pairs for any user. This will act as an automatic sign up for us in this case

• Create the client application

  • A program users to send messages securely using encryption and authentication.
  • Sends the hashed userid of the agent to the server upon connecting.
  • Receives the number of saved messages from the server and retrieves them.
  • Verifies the server's signature, decrypts the message, and displays it on the screen.
  • Prompts the user to enter the recipient userid, message, and sends them to the server.
  • Generates a signature based on the message, and sends the encrypted content, timestamp, signature, and unhashed sender userid to the server.
  • Prints the date, message, and prompt for the user to enter a new message.

• Create the server

  • Storage for messages sent by user that are not yet read by their recipients.
  • Listens for incoming connections from clients at the specified port.
  • Handles one client connection at a time.
  • Has its own private key and the public keys of all users.
  • Uses RSA/ECB/PKCS1Padding for encryption and SHA256withRSA for signature generation.
  • Stores messages in memory in encrypted form, ready to be sent to the recipient.
  • Sends saved messages to the client, deletes them from the server, and verifies the signature.
  • Computes the hashed recipient userid for storing and locating saved messages.
  • Re-encrypts the message with the recipient's public key and saves it in memory.
  • Prints the hashed userid of the client, sender and recipient userid, timestamp, and plaintext message contents for marking purposes.

To sign up a user, run java UserSignup. A prompt will appear asking for a username.

Note: Your username must be all lowercase

• The server has to started first after compiling it.
• To start the server: java Server <Port number>
• Proceed to start the client: java Client <host> <port>
• After Logging in the Client can send messages and see if he/she has any message sent to him.