securedChatServerClient

An application developed with python 2.7, for a secure communication between clients, the server in this application authenticated users, and generation symmetric keys for peer users communication

Execution example

starting the server

python ./Server/server.py 

starting the client

python ./Client/client.py 

the CLI handeled by the client application

authentication

auth USERNAME PASSWORD

signing up

sign USERNAME PASSWORD

sending a message to userX

send userX message

requesting the list of connected users

list

The packacges used in this aplication

cryptography with fernet for key generation and message encryption/decryption also RSA for key encryption

bcrypt for password hashing

tinyDB to store username's and passwords in a json file

PyYaml to read configuration file

socket for network communication TCP dadatgram between client and server, and UDP datagrame between clients.

Configuration Files

client configuration file

specify the ip address and the location of the server certificate

cat /Client/config.yaml
server_address: localhost
server_port: 10000
server_certificate: ./KeyA_/A_certificate.crt

server configuration file

sepecify the ip address of the server, the location of it public and private keys, and the json file were are the passwords stored

cat /Server/config.yaml
server_address: localhost
server_port: 10000
server_certificate: ./KeyA/A_certificate.crt
server_privateKey: ./KeyA/A_privateKey.key
data_base: pass.json

Instant messaging system Architecture

The architecture is based on a client server system for authentication and a client to client communication

Server

With a private and public keys

• The server maintain a database mapping usernames and hashed passwords
• The server permit to a user to sign up and authentify himself
• The server inform each connected client by any new connected or disconnected user and also, a list of all connected client
• The server generate a symmetric key when a user want to communicate with another user, and communicate it to both users

Client

With the server public key, client server authentication

• First Step: the client enter his username and password, the application will hash the password, and generate a symmetric key K, then send to the server Pubk[K]:K{USERNAME:Hash(Password)}

• Second Step: the server receive a new connection followed with the message Pubk[K]:K{USERNAME:Hash(Password)} with the server private key decrypt Pubk[K], then decrypted K{USERNAME:Hash(Password)}, check if the credential are in the database if it is the case send K{‘True’} otherwise send K{‘False’}

• Third step: user receive K{(‘False’|’True’)} decrypt the message if False ask the user to reenter the username and password and resend the authentication message to the server; otherwise if it is True it send back to the server the address of the Datagram Socket for peer client message

Client request to communicate with another user

When a user Y for the first time after his authentication, want to send a message to another connected user X:

• Client Y send a request to the server, for the address and a symmetric key to exchange secretly with X
• At the reception of this request by the server, it generate a key and send it back to both users X and Y
• from the received server message Client X will know that he will be expecting a message from Y and therefore he has the key Kxy to decrypt the received message from Y and also to encrypt messages for Y