Re: Anonymous browsing (was Re: Getting Back to our Radical Roots)

[tzeruch@ceddec.com]

On Fri, 20 Jun 1997, Jeremey Barrett wrote:

> X-Premail-Auth: Good signature from user "Jeremey Barrett
>    <jeremey@bluemoney.com>".

> Anonymous web browsing is definitely being worked on. However, simply
> chaining proxies ala remailer chains is not sufficient because traffic
> analysis is fairly trivial.
> 
> The question is what's the threat model. If the goal is to prevent the
> server from identifying the client given limited resources, then
> www.anonymizer.com or similar is sufficient. However, the real problem
> is preventing an entity with unlimited resources and control over most
> of the nodes in the anonymous network from conducting successful traffic
> analysis. This is an entirely different and very difficult problem.

Having got the latest Applied Cryptography, it looks like it would be
possible to set up a series of servers on the "Dining Cryptographers at a
Disco" model.  It would require a constant flow, probably something like
token ring, so couldn't be used for high bandwidth applications, but it
completely nukes traffic analysis.

(as an aside, if someone has control of "most of the nodes" they can cheat
however they want without resorting to traffic analysis - if they
control few nodes the picture is different).

[brief but wrong description: assume there are an even number of servers. 
Each generates a random number and passes it on along with a parity bit. 
Then next server compares it's random number with the previous one and
flips the parity bit if the random bits *differ*, and then sends the
parity bit and the same random bit to the next server. When the bit has
completed the circuit, the parity bit will be zero (which would be
broadcast or send in the next round), unless someone altered it
intentionally.  So any one can set a one bit by simply not flipping it,
and no one will know who since all anyone knows is the original state of
the parity bit when they saw it, and the previous random number.  If a
series of bits is encrypted using a public key, then only the recipient
will be able to receive it, and in all cases no one will know who sent or
received the message.  You need collision detection like ethernet, and
some addressing stuff, but all the extra bandwidth obscures the sender
and recipient.  Someone please post a clearer description]