jhchat

UPDATE

haven't taken security course when I made this. If I were to make such app now, a few changes would have been made:

• Instead of plain TCP connection, I would look for TLS libraries
• Dilemma below could be solved by either
  • trust a Certificate Authority
  • adopt DPKI, make use of block chain to exchange key pairs
• Use thiserror to define my error types
• Use tonic (grpc) or axum (http) instead of making my own protocol
• Replace the encryption library by openssl bindings
• Avoid some silly code in my current perspective

Goals

• Users do trust Client (They build it from source)

• Client can decide not to trust Server (By default public keys are exchanged through server)

  • User may manually set other's public key via third party communication
  • A pre-configured dummy message is sent if the key delivered by server is not identical
    • with warnings on client side
    • dummy message is encrypted by server's public key
      • Client behaves as if it hasn't discovered Server's fraud

• Client can decide not to trust user's device

  • Private key is encrypted on local disk and decrypted by server during connection

In short, this project assumes that the server and the current computer user are malicious. Our goal is to have each potential hostile hold one piece of the puzzle, so that information leaks only if they refer to the same individual.

Dilemma

It is quite inconvenient to manually exchange public keys when users don't trust the server, but for now I am not aware of any alternative solution.

Ideally, users expect the following would happen when they send a message

However, no one can prevent the server from doing this

MileStone

Feature	Status	Source Path	Lib
Application Protocol	Done	core/src/codec/msg_codec.rs	tokio-util
Message Delivery	Done	server/src/process.rs	N/A
Log	Done	server/src/init.rs	tracing
Config	Done	core/src/config.rs	serde + toml
Client Encryption	Done	core/encryption/rsa_impl.rs	RustCrypto/rsa
Customizable Encryption	Done	core/traits/encrypt.rs	N/A
Exchange Public Key	Done	server/src/process.rs	N/A
Offline Pubkey Mode	Coming Next		N/A
Update Key Strategy	Coming Next		N/A
Authentication	To Do		TBD
Unsafe Group Chat	To Do		N/A
Expensive Group Chat (e2ee)	To Do		N/A
File Server (RSA + AES)	To Do		RustCrypto/aes
Encrypt Private Keys on Client	To Do		TBD
Chat History Persistence	To Do		diesel
Horizontal Scaling	To Do		TBD

Build From Source

Prerequisit: rustc 1.71

git clone https://github.com/realzhujunhao/jhchat.git cd jhchat cargo build --release