I started writing a WebSocket server that will act as an "router" between smart home controllers and mobile applications used to control and monitor systems. Naturally smart home controllers can also save data into cloud.
I am thinking about what would be the best way to authenticate smarthome controlllers and mobile applications. Traditional approach would be to login with username and password but as I want my server to be as secure as possible, would ed25519 based public key authentication be a better option?
Server program and mobile clients will all be 8th applications and 8th supports more crypto stuff out of the box than I will ever need.
As connection is made over https, there is probably no need to encrypt the communication channel. So, something like following would work:
- Client sends it's public key to server
- Server checks that public key exist inside the user database, responds with a challenge message and computes hash based on this message
- Client independently computes the message hash, passes private key and hash for cr:ed25519-sign and sends result back to server
- Server uses public key, hash and signature buffer from the client to authenticate the user with cr:ed25519-verify
Other possibility that allows encrypting messages between server and clients is:
- The client sends its public key to the server. The server creates a shared secret (servers private key, client public key) which it uses to encrypt a randomly generated session-key to the client.
- If the client is sending an invalid public key, no communication is possible and the server drops the connection.
- If the client is sending a valid public key, it knows the shared secret (servers public key, client private key) and uses that to decrypt the session key.
- Now session key can be used to encrypt data over channel
