DNS BBS

This is a minimalist BBS, or maybe a web 2.0-style forum, except it runs entirely over DNS. I got the idea for it after doing a deep dive into the different covert channel communications techniques used by modern malware. This BBS is:

• stateless (no sessions)
• anonymous, usenames optional
• append-only
• clunky
• fun!

Build

This BBS has only been tested on Debian amd64. Absolutely no thought whatsoever was given towards compatibility on other architectures or operating systems. In theory, it should run anywhere Docker and SBCL run.

wtf

Rationale: https://0x85.org/dnsbbs.html

Depending on when you read this page, there may be a demo running on bbs.stackgho.st. Try:

$ dig @bbs.stackgho.st -p 31337 wtf.bbs.stackgho.st TXT

Topics

A list of topics can be retrieved via:

index.bbs.example.org TXT

Available topics are returned as a semicolon-separated list. For example the "dev" and "misc" topics would come back as such: t=dev,misc. Information about a topic is available via:

meta.misc.bbs.example.org TXT

This will return the topic description and the id of the most recent message, like so: desc=General discussion;latest=1

Reading messages

Once you have the ID of a message it can be retrieved like so:

msg.<id>.<topic>.bbs.example.org TXT

Or, for messages too long for a single response that have been chunked:

msg.<id>.<page>.<topic>.bbs.example.org TXT

Messages are returned base64-encoded (because only leet haxors use base64 of course)

Posting messages

Posting messages is accomplished by Base32-encoding the message contents.

post.<b32(msg)>.<topic>.bbs.example.org TXT

If the message is too long, it must be chunked:

post.<b32chunk>.<nonce>.<seq>.<topic>.bbs.example.org TXT

In this last query, <nonce> is a short client-supplied random string (e.g. a hex string like a3f9) that uniquely identifies the posting session. This prevents chunk buffers from colliding when two clients behind the same NAT post simultaneously. <seq> is an integer sequence number beginning at 0 and increasing from there. The final chunk is signified by passing the string end for the sequence number, rather than an integer.