Key distribution with centralised server

A centralised Key Distribution Centre is responsible for storing user details including user name, ip address, user port number, and a hash digest obtained from combining passphrase with name. This hash digest is used as 'salt' to derive the secret key shared between a particular client and server. For client-server interaction, messages are encrypted using this obtained unique key for each client. A client 'A' who wishes to communicate with another client 'B' registered with the same server approaches the server so that a session key can be generated for secure interaction between both involved parties. The server encrypts this session key and other details required for authentication with the respective shared secret keys with the clients A and B. This message from the server can only be decrypted by these 2 clients ensuring secure distribution of a symmetric key.

Setup Instructions

sudo apt install python3
sudo apt install python3-pip
pip3 install cryptography==3.3.1

Running Code

Make sure pwd.txt is present before running code(either as an empty file or with details of already registered user). Input message to be sent is to be stored in a file in.txt

1. KDC

./kdc -p <kdc_port_no> -o out.txt -f pwd.txt

2. Client - Reciever Register the reciever client(if not previously registered) with KDC and wait for message from sender on port number 60000.

./client -n <reciever_name> -m R -s outenc -o outfile -a 127.0.0.1 -p <kdcport>

3. Client - Sender Register the sender client(if not previously registered) with KDC.

./client -n <sender_name> -m S -r <reciever_name> -i in.txt -a 127.0.0.1 -p <kdcport>

Follow along with the prompts to complete process of sending a message. Script files of a sample run are available in "SCRIPTS" folder

NOTE:

• Reciever client should be run before sender client.
• All communications are between ports within localhost.
• InvalidToken error is raised and socket is closed if passwords used do not match.