johanhenriksson / d2prox

Diablo II game proxy

d2prox

Diablo II proxy written in Go. Proxying allows the user to bypass IP rate limits set by battle.net. Application-level proxying is achieved by deep packet inspection and modification.

Since the code allows modification of any D2 packet, it could theoretically be used as a base for packet editing, packet filtering and implementing packet based hacks & bots.

Disclaimer

This software is unfinished and not yet properly tested. It's only meant as a proof of concept. Don't use it on battle.net.

Configuration

Environment variables:

• REALM (string): Realm hostname. Defaults to europe.battle.net
• LOCAL (bool): Indicates whether the server runs on a local or remote machine. If true, the proxy can only be reached from the local machine. Otherwise, its public ip is looked up and used for proxying. Defaults to true

How to use

• Rewrite europe.battle.net (or your desired realm hostname) to the proxys IP address in your systems hosts file. If the proxy is running in local mode, this will be 127.0.0.1. Otherwise, it should be the proxy machines public IP address.

  Example: (/etc/hosts)

  127.0.0.1 europe.battle.net
  

• Run d2prox

  Using docker-compose:

  docker-compose up
  

  By building the go executable:

  go run cmd/d2prox.go
  

• Login and play

Method

It works by implementing 3 separate proxies for Battle.net, the Diablo 2 Realm Server and the Diablo 2 Game Server. Application-level proxying is achieved by deep packet inspection and modification.

The basic idea is as follows:

• Configure the system to resolve _realm_.battle.net to the proxy ip
• Client connects to our battle.net proxy
• Once the player authenticates, battle.net sends the realm server ip to the client (SID_REALMLOGONEX). This packet is intercepted by the proxy, and replaced with 127.0.0.1. The original realm server ip is stored in a map which correlates clients (using the MCP tokens) to realm server ips.
• Client connects to the realm server proxy
• Client sends MCP_STARTUP containing its MCP token. The MCP token is used to retrieve the original realm server ip, and a connection is opened to it. From now on, all traffic is forwarded to the real realm server.
• Client creates or joins a game. MCP_JOINGAME is intercepted, and the game server ip is also replaced with 127.0.0.1, and a token is used to map the client to this original ip.
• Client connects to the game server proxy
• Client sends D2GS_GAMELOGON with the game token, which is used to retrieve the original ip and connect to the game server. From now on, all traffic is forwarded to the real game server.