Assignment Task

Developing a Secure Peer-to-Peer Chat App

You are required to build a secure, asynchronous, peer-to-peer chat application. Network communications must be via TCP. The flow of the program should be:

1. Start the program.
2. Ask the user for the following information:
   • A port on the machine to act for incoming connections.
   • The name of a file containing a directory of individuals that can be contacted.
3. Open Server TCP socket locally on the port specified by the user.
4. Load the user directory (specification below). This is a JSON serialized dictionary format.
5. Wait for either an incoming network message or a message to be sent, typed by the user.
6. If there`s an incoming network message:
   • Connect to the destination using the secure protocol, which must include:
     • The generation of key material as shown below.
     • Mutual authentication of the outgoing connection.
     • Establishment of a secure channel using SHA256 HMAC and AES256 CBC Cryptography.
   • Receive Message – Message format below.
   • Check the control information for consistency.
   • Display the received message to the user.
   • Terminate the connection.
7. If there`s a message to be sent:
   • Wait for the message to be completed (Your choice of end indication).
   • Request the destination from the user. This should be selected from the directory, but you should also provide a manual option to directly specify IP address, port, and password.
   • Open a socket to the destination.
   • Connect to the destination using the secure protocol, which must include:
     • The generation of key material as shown below.
     • Mutual authentication of the outgoing connection.
     • Establishment of a secure channel using SHA256 HMAC and AES256 CBC Cryptography.
   • Send Message – Message format below.
   • Display transmission success or failure message to the user.
   • Terminate the connection.
8. Go to step 5.

Message Formats

You should use a Python Dictionary message format that can be serialized as follows:

User Directory Format

Type of HMAC in use: SHA256
Type of encryption in use: AES256CBC

You should use a Python List of Dictionaries for the directory format, which can be serialized:

Additional Requirements and Information

• Before starting to write your application, plan the way you will develop features.
• Use the user name in the CHAP messages to select the incoming information for the key.
• Passwords should not be used directly for CHAP, HMAC, and crypto keys. Utilizing a key derivation function will be rewarded with higher marks.
• All messages sent and received should be logged with appropriate security to protect their confidentiality and integrity.
• All keys MUST be lowercase.
• All msg_type values must be lowercase.
• Where there is no explicit body (ack or nack), the body value is the serialized version of the NoneType or None.
• PDUs MUST be serialized as a string and encoded using utf-8.
• You may wish to delay the implementation of the user directory functionality to aid simplicity in building the system. However, a user directory is needed for higher marks.
• Any messages received out of a time window of 25 seconds should be ignored.
• Use a 32-bit Cyclic Redundancy Check calculation from the zlib library in the Message header.
• It is highly recommended to use an object-oriented approach.
• You must only use primitive cryptographic libraries and not utilize protocols such as SSL/TLS.
• It is highly recommended to use some form of FSM for the management of the communications protocol.
• Use comments extensively to explain your code.
• Include a short .txt file that explains any security weaknesses you think are present in the approach.