Dev/DHCP

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Design Documentation Whonix DHCP Server

If Whonix had a DHCP server running on eth1 on Whonix-Gateway™...[edit]

Advantages:

  • Setting up Multiple Whonix-Workstation™ would be simpler.
  • In particular, you could trivially clone an existing workstation instance (including the unmodified standard template), use it, and delete it... or even run it with all "disk writes" done only in RAM.
  • Using Other Operating Systems would be simpler.

Disadvantages:

  • Higher attack surface due to DHCP?
    • Anything obviously creates attack surface. DHCP itself is a simple protocol, but that doesn't mean it has zero risk.
    • ISC dhcpd is the reference implementation:
      • It's probably more complicated than you'd like to see, because it provides so many facilities for conditional responses.
      • On the other hand, it's mature, heavily used in exposed places, and much of its attack surface is probably only reachable from the server side.
    • There are other implementations.

Needs research:

  • Does DHCP have some feature which a compromised Whonix-Workstation could abuse? Does DHCP have a feature such as "tell me the IP of your upstream router"?
    • Answer:
      • The basic idea behind DHCP is that the client tells the server some things it knows about itself and asks the server to tell it more.
        • The "things" are attribute-value pairs that use well-known numeric attribute identifiers, some of which are reserved for local customization.
        • The client usually asks for specific attributes. The server is free to leave some out or add unrequested ones.
      • There is no standard attribute for "IP of your upstream router" because that's not useful. It would be possible to add it, but that would require server support.
      • DHCP servers can be configured to forward requests to upstream servers, which may be routers. That is a server-side configuration option, and a client can't ask the server to do it.
      • Any reasonable DHCP server can be configured to give clients only a fixed set of attributes chosen by the server.
      • DHCP server code, in general, gives the admin a huge amount of control over the information it will provide to clients. You could certainly configure ISC dhcpd to give only X or Y attributes.
    • TODO: Read this stuff...

If Whonix had a DHCP client running on eth0 on Whonix-Workstation...[edit]

Disadvantages:

  • Needs research: Some users with little knowledge only download Whonix-Workstation and set its network settings to DHCP. (example) Accepting any IP from DHCP would allow them to non-anonymously use Whonix-Workstation easily. We would have to add some protection to avoid accepting an IP from VirtualBox NAT, if that is possible.
  • Needs research: Configuration of Onion Services could become more difficult because these need a fixed internal IP?
    • No. DHCP typically assigns only addresses from a configured range within a subnet. If you want a host with a fixed address, you give it an address outside the dynamic range. You can also configure a DHCP server to always assign a given IP address to a given MAC address or other host identifier, although that's not necessarily something you'd want to rely on for a hidden service.
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