Miscellaneous suggestions/Centralised authentication

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A proposal by MarkR.


Why we need it

  • To run leagues we need persistent authentication
  • To prevent server admins from being able to get passwords

How authentication works now

We just have two passwords, one server password for creating a new company, and one for connecting to an existing company. Passwords are stored in memory on the server and sent in plaintext, in the clear.

The list server does not do any authentication on servers - the server name is not checked against IP.


Client decides it wants to connect to server X:

  • Client connects to the OTTD server, and asks to be authenticated
  • Server creates a random number R1 and sends it to client, also keeping a copy. R1 is associated with a given client only, and will be different each time.
  • Client sends its username, password and R1 to the auth server
  • Client gets back a session ID which is only valid in conjunction with that R1 value for some short period of time ( a few minutes or something)
  • Client sends its username + session ID to the OTTD server
  • OTTD server sends username + session ID + R1 to auth server saying "Is this valid"?
  • Auth Server replies, saying "Yes" or "No" and OTTD server allows or denies client respectively


  1. . Client never sends username / password to OTTD server (as currently)
  2. . R1 value means that sniffing the session ID is useless, as another server will use a different R1 value
    (and indeed the same server will use a different R1 value if you connect again)
  3. . Man-in-the-middle attack is still possible unfortunately, by using a modified server which also behaves as a client and "passes through" the authentication. Once it's authenticated, this modified client can do a session-hijack.
  4. . In the interim, if we're super-worried about the security of passwords being sent in the clear/to server owners, it should be a relatively trivial issue to implement a quick salting & hashing system. For a game server this is probably overkill.
  5. . Also, wouldn't it be neat using OpenID? I totally fail to see how this would work, but it's an interesting thought.


  • We're going to need a UI to set the username/password before connecting to any server
  • We're going to need (ideally), in-game registration on the main menu.


  • How to play co-op? Some sort of invite system? Currently co-op is frequently abused.
  • Can server admins allow unauthenticated clients? If so, do we indicate them somehow to other players?
  • Should the client store the default username/password locally? If so, where?
  • How does this affect LAN based play, without access to an authentication server?
  • What if a server admin wishes to completely opt out of centralised authentication?
  • Maybe OTTD shall not reinvent the wheel and use GSSAPI for auth?
  • How does the central server identify itself? host-name? IP? ssh_host_rsa_key.pub?
  • Who manages this server? How do we trust them?
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