dns-tunnel

DNS Tunnel

DNS

This contains a short implementation of the DNS protocol, inspired by the documentation from @EmilHernvall https://github.com/EmilHernvall/dnsguide/blob/master/chapter5.md

Tunnel

The basic tunnel is looking like that:

The tunnel is communicating only via TXT records, sending data happens in the following steps:

Client -> Server

1) Client sends a DNS Question for the TXT record to INIT.domain.com to check if the server answers 2) For a correct answer, the TXT Record must be set to ACK 3) Sending a payload consists of the following messages:

- DNS Request with `START.domain.com`
- DNS Reply with `ACK`
- DNS Request with `somedatahere.domain.com`
- DNS Request with `somedatahere.domain.com`
- ...
- DNS Request with `END.domain.com`
- DNS Reply with `ACK`

Server -> Client

1) The client sends regular POLL requests 2) The server will provide the data to send in the TXT Record 3) Approach is the same:

- DNS Request with `POLL.domain.com`
- DNS Reply with `START`
- DNS Request with `POLL.domain.com`
- DNS Reply with `herecomesthedata`
- DNS Request with `POLL.domain.com`
- DNS Reply with `herecomesmoredata`
- DNS Request with `POLL.domain.com`
- DNS Reply with `END`

For the complete communication, the data is first "encrypted" via xor() and then base64 encoded to hide the payload at least a little bit