(dis)advantages of DC-Net vs remailers

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tcmay@netcom.com wrote:

> Chaumian digital mixes--what you Americans call "remailers"--mainly
> solves the sender anonymity problem. Message pools, or broadcast to a
> group or site that includes the receiver, mainly deals with receiver
> anonymity. The combination of the two deals with both.
> 
> Both are solved elegantly with the Dining Cryptographer's Protocol,
> about which much is written on this list every few months. Messages
> are "sent" in an Ouija-board fashion and received by the person who
> can successfully decrypt a public message sent over the system.

I tend to favor remailers + broadcasting + anonymous-return-addresss
over the DC-Net protocol.  Let me list some of their relative 
advantages and disadvantages.  Please add to these if you can think
of more...

Advantages of DC-Net over remailers

	- more flexible trust relationships - you can add your buddies to 
		the set of people who have to be compromised to trace you
	- lower latency - don't have to wait for remailers to collect enough 
		mail for batches
	- untracibility need not depend on assumptions about the enemy's
		computational power

Disadvantages of DC-Net

	- complexity - explaining the core concepts of a remailer takes only 
		a couple of lines, as opposed to a couple of screens for a DC-Net
		Implementation of a DC-Net seems to be an order of magnitude
		harder as well.
	- more vulnerable to denial of service attacks
	- MUCH higher bandwidth costs

I think over the long run the last factor will be most important.  In 
a DC-Net, for each bit one participant wants to send to another, EVERY
OTHER participant must broadcast a bit to ALL participants.  I can 
imagine a remailer-net with one million users, but I don't see any 
possibility that a DC-Net can be scaled to that size.

Wei Dai


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E-mail: Wei Dai <weidai@eskimo.com>   URL: "http://www.eskimo.com/~weidai"
=================== Exponential Increase of Complexity ===================
--> singularity --> atoms --> macromolecules --> biological evolution
--> central nervous systems --> symbolic communication --> homo sapiens
--> digital computers --> internetworking --> close-coupled automation
--> broadband brain-to-net connections --> artificial intelligence
--> distributed consciousness --> group minds --> ? ? ?

On Mon, 6 Feb 1995, Wei Dai wrote:
 
> I think over the long run the last factor will be most important.  In 
> a DC-Net, for each bit one participant wants to send to another, EVERY
> OTHER participant must broadcast a bit to ALL participants.  I can 
> imagine a remailer-net with one million users, but I don't see any 
> possibility that a DC-Net can be scaled to that size.

Not so -- you merely have to broadcast to enough people.  
But then the topology, and hence the complexity, gets worse.

This however merely reduces the bandwidth waste from n^2 to n*lg(n)


A further wrinkle -- forming DC nets of DC nets, can reduce the
bandwidth waste to lg(n)^2, which should scale adequately to cover
the cosmos, but then the complexity gets really scary.

And when you try to figure how to deal with denial of service
attacks in a big DC net that tries to use bandwidth with
tolerable efficiency -- I don't know if anyone has figured out
what would be involved -- I certainly have not.


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