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End to end messaging system like WhatsApp

Your task will be to design an end to end messaging system like WhatsApp with the below functional- ities:
• Multiclient chat application that has a server component and 4 clients [atleast].
• The system should support the signup and sign in feature. [error message with wrong credentials].
• User can send message to other user [p2p message] [ SEND command] [ ]
• Each user can join multiple chat rooms (groups) at a time.
• Each user can list all the groups. [LIST Command] [show all group and number of participants in each group]
• Each user can join a group [JOIN command]. If the group does not exist then the first create it then joins it.
• Each user can create a group [CREATE command].
• If one user sends a message to a group it should be sent to all members of that group.
• The message is encrypted using Tripple DES (3DES) and the key will be Diffie–Hellman key type exchanged between clients.
• For each group make one key (random nonce).
• Message can be any type, for example, text, images, video, and audio.
Note: The one time Diffie–Hellman type key must be include a prive key (for instance roll nos.).

For End to end encryption, we have done following: 1) For direct peer to peer For chat message

  • First a secret key a generated on both sides using Diffi-hellman.
  • Message is encrypted and decrypted using the same key.
  • Everytime a new key is generated, even if the 2 end might have done communications in the past.

For Sending File

  • First a signal message is send indicating the receiver that it's receiving a file and not a text message so that it runs code to receive file on it's end.
  • Now key is generated using Diffi-hellman and is used on both ends.

2) For Group messaging

  • When a group is created, a secret number is generated on server side, this is shared with group creator using his password as the key.
  • When other peers join group, they get the key from server using their password as key.
  • For sending message in group, first a signal message to each group member to indicate that it's a group message GROUP SIGNAL SYNTAX GROUP <GROUP_NAME> for text message GROUP <GROUP_NAME> <FILE_NAME> for sending file in group
  • This indicator message informs receiver to decrypt using the specified group mentioned in the signal message.

List of Commands

- For Running Server

python3 server.py 
Eg. python3 server.py

- For Running Server

python3 clienr.py <port_number>
Eg. python3 client.py 5000

- For sending message to a single client:

SEND <Username> <Message>`
Eg. SEND a Hello

- For sending message in a group:

SENDGROUP <Groupname> <Message>`
Eg. SENDGROUP xyz Hello

- For creating a new group:

CREATE <Groupname>
Eg. CREATE xyz

- For joining a group:

JOIN <Groupname>
Eg. JOIN xyz

- To show all the groups available:

 LIST

- For sending file to a single client:

SENDFILE <Filename> <Username>
Eg. SENDFILE abc a

- For sending file in a group:

SENDGROUPFILE <Filename> <Groupname>
Eg. SENDGROUPFILE abc xyz