openssh unix dev - Aug 2021 - SSH as discard server?

Before I go about reinventing the wheel I thought I would ask here.

I'm doing some development in SSH and it would be helpful if I could 
isolate certain aspects of what I am working on. What I would like to do 
is have an SSH aware discard server that accepts an inbound connection 
from an SSH client and then dumps every incoming packet into a black 
hole. I don't want to process, decrypt, or otherwise do anything with 
those packets post authentication. Switching to a none cipher won't work 
as it would require both ends to renegotiate to none. Likewise, just 
redirecting the output to /dev/null means I'm still spending cycles 
decrypting and verifying the HMAC.

So does anyone know of any existing implementations that can do this? If 
not, does anyone have any suggestions as to where to start? I'm thinking 
that adding a new CFLAG so I can do a discard in in cipher_crypt would 
be reasonable but I wanted to get any thoughts people might have.

e.g. 	if ((cc->cipher->flags & CFLAG_DISCARD) != 0) {
		return 0;
	}

Thanks,

Chris

After authentication, the ssh client is almost certainly going to 
request a channel.? If you don't acknowledge that, it will hang. It can 
then request further channels at any point during the connection.? 
Handling this requires decrypting the traffic.? Any "sink" server that
doesn't bother to decrypt packets will need to be written in a way which 
is very specific to the way the client uses SSH.

 From the intro to rfc4254:

    This document describes the SSH Connection Protocol.  It provides
    interactive login sessions, remote execution of commands, forwarded
    TCP/IP connections, and forwarded X11 connections.  **All of these channels
are multiplexed into a single encrypted tunnel**.

(my emphasis)