README

Robert Li
CIT 595 Final Project
Mini-RSA Chat

This project is a 2-way chat program. written in Java, that encrypts all 
messages using the RSA encryption algorithm. It first exchanges public keys 
with its counterpart, then encrypts each message sent with that public key. 
Messages received are then decrypted with the private key.

It also includes an application to generate an RSA key pair, as well as an 
application to crack an RSA public key via brute force.


-----INSTRUCTIONS-----

STARTING THE PROGRAM

To run the program, you can use the included Makefile. The following commands 
are available:

 make runserver - Compiles, then runs the chat server on port 8484.
 make runclient - Compiles, then runs the chat client using host localhost and 
                    port 8484
 make runkeygen - Compiles, then runs the RSA key generator with the 50th and 
                    100th prime numbers.
 make runcrack  - Compiles, then runs the RSA key cracker with the public key 
                    (2729, 3149).
 make build     - Compiles all .java files to .class files.
 make clean     - Removes the compiled files.

After compiling, you can run the programs with the following commands:

 Server: java chat/ChatClient -s <port number>
 Starts a server, which listens on the specified port number.

 Client: java chat/ChatClient -c <host>:<port number>
 Starts a client, which attempts to connect to a server at the specified host 
   and port number.

 Key Generator: java minirsa/Keygen <n> <m>
 Generates a random RSA key pair using the nth and mth prime numbers.

 Cracker: java minirsa/Cracker <e> <m>
 Using a brute force algorithm, 

Note that the server must be running and listening before the client attempts 
to connect.

PROGRAM FLOW

The chat programs, when they first start, will prompt the user for their RSA 
key. The server will then listen for a connection on the specified port, and 
the client will attempt to connect to the specified host.

After the connection is made, both programs will spawn a reader and a writer 
thread. The writer thread will prompt the user for input, encrypt it, then 
write it to the opened socket. The reader thread will read from the socket, 
decrypt the message, and write it to the screen.


-----PROGRAMMING NOTES-----

APPROACH

We started by writing the Mini-RSA library functions, which took us back to CIT 
592. Next, we wrote a basic server and client, allowing the two to connect and 
send messages back and forth. To make the chat full duplex, we implemented 
threads, one for reading and one for writing. Lastly, we incorporated the RSA 
encryption and decryption for the writer and reader, respectively.