From: cman@IO.COM (Douglas Barnes)
Date: Sat, 9 Oct 93 18:30:59 PDT
To: newsham@wiliki.eng.hawaii.edu (Timothy Newsham)
Subject: Re: DC-Net proposal,  comments requested
In-Reply-To: <9310091935.AA17001@toad.com>
Message-ID: <9310100127.AA23557@illuminati.IO.COM>
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> A DC-NET
>    This net is broadcast in nature (data written by one machine can be
> seen by all other machines on the network) but with the characteristic 
> that it is impossible to tell which machine on a particular DC-Net 
> wrote out the data (except if all other machines are controlled by the 
> same person?).  The DC-NET itself is bit oriented.  Such a DC-network would

Actually, a single collusion between two processes could isolate a 
single non-colluding process, if that process was "between" them 
on the graph. One of the hard problems with DC Nets is how to minimize
the need for trust among the members, and how to arrange for net
formation and re-formation in a way that minimizes the ability to
deliberately or systematically partition all of the processes over
a period of time as part of a "fishing expedition" to determine the
source of some perceived-noxious output from the net.

We talked about DC Nets at the Austin cypherpunks meeting, and played
the "Dining Cryptographers Game" (complete with snazzy pieces provided
by yours truly). It was fun, but folks were a little nonplussed about 
the degree of trust required among participants.

> be the underlying layer for the packet network.  The actual DC-Network
> would be made up of processes on various (or even the same,  for testing 
> purposes) machines all connected together with TCP.  
>  
> 
> The Packet Net
>    The Packet Network would be built with the DC-Net as a base.  In order
> to send useful information across the network a single node would form
> data into packets.  These packets would be outputted to the network a
> bit at a time.  Since the DC-Net is bit oriented it is possible for

I've been looking at this problem as well, Tim, and it doesn't seem to 
me that you have to output a bit at a time. In fact, the DC net machines
should probably be operating on blocks that fit nicely into single IP
packets. Just consider the blocks to be the result of N coin tosses.

> another node to send some bits after one node has started to write out
> its packets.  As a node writes out a packet it should listen to the
> network for "collisions" and if a collision is detected it would 
> "give up" on the current transmission and wait for some time to start
> again.  Packets from one machine to another must have some sort of
> addressing.  The packet could be encrypted entirely in the public
> key of the destination if there is only a single DC net.  If there
> are multiple DC-Nets with packet forwarding between them then there
> must be some sort of plaintext address information in the packets.
> The return address should *never* be in plaintext.  Probably the
> data and return address of a packet would be encrypted in the public
> key of the destination or in a private key shared with the destination.
> 
> Sessions
>   Virtual connections can be built on top of the packet network in
> the same way as they are on top of other packet networks.  Some protocol
> like TCP (or even the TCP protocol) could be used.
> 
> 
> Why should this be built on the internet?
>     Writting and debugging a network of this sort on top of the internet
> should be easier than writing it and implementing it from scratch.  Some
> people have proposed neighborhood networks that would be used to
> implement untraceable and unstoppable connections.  This is an excellent
> way to develop and debug such a network.
> 
> What needs to be resolved
>    Alot!  This is just something I threw together.  There are alot of
>    questions.  In fact most of it is still a question.  The protocol
>    of the underlying DC-Net needs to be written.  A packet layer must
>    be written or adapted from current protocols.  The issues of addressing
>    need to be addressed.  There are also sure to be alot of politically
>    oriented questions as well.
> 

One head scratcher I've been considering is whether it would be better
to simulate a token-passing scheme, or to have comparisons broadcast
to all participants. Since in a broadcast scheme, the number of packets
per round generated is n^2, it seems prima facie that token passing would
be faster (it would certainly consume a much smaller % of the net's total
bandwidth), but actually for reasonable n, the accumulated latencies from
a few slow links could very well make the token passing slower. 

Also, I have thought of some ways of dealing with "slacker" processes
or folks who suddenly drop out that work better with a broadcast approach,
but there's probably a way to deal with them in the token-based scheme.

Another issue is whether or not your processes need to elect a "lead" process 
to handle synchronization issues and serve as an arbiter in net formation
and re-formation.


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