[freehaven-dev] Re: Blocks

[Michael J Freedman <mfreed@MIT.EDU>]

------- Forwarded Message
From: "Blat Froop" <petergunn@hotmail.com>
To: mfreed@MIT.EDU
Subject: Re: Blocks
Date: Mon, 31 Jul 2000 13:49:52 GMT

>From: Michael J Freedman <mfreed@MIT.EDU>
>To: petergunn@hotmail.com
>CC: freehaven@freehaven.net
>Subject: Blocks
>Date: Sun, 30 Jul 2000 23:08:00 -0400
>
>Peter,
>
>I wanted to introduce myself as somebody also interested in anonymous
>publishing systems.  I've been working with a few other colleagues
>on the Free Haven system (http://freehaven.net), which focuses more
>on content-neutral, long-lived storage.  You can find more information
>at our site, as well as the paper we recently presented at the Berkeley
>conference on Design Issues in Anonymity and Unobservability
>(http://freehaven.net/papers).
>
>Anyway, I came across the Blocks project, and was wondering if you could
>explain the "anonymity" features to a greater extent.

Hi,

first I'd better give you a little background to Blocks... Blocks
was started as a prototype to investigate possible new algorithms
for things like routing and searching, for distributed file
sharing applications like GNUtella and Freenet. However, GNUtella
seems very disorganised, and Freenet to slow to bring out a
useable version... so the Blocks prototype has had quite a lot
of interest, and it looks like Blocks may eventually become a system
in its own right (if it isnt already). But the downside is that
Blocks was never properly designed to be either very efficient,
very useable, complete secure, or completely anonymous.

Eventually I will have docs on the website, but its been time consuming 
getting things set up and getting Blocks into a useable state.

Basically Blocks anonymity features rely on the fact that unless
you can break the cipher or PRNG, you shouldnt be able to tell
whats in the disk cache or what passed over the network unless
you are directly connected to the server in question, or active in
a man-in-the-middle attack. A new feature in 0.14 which allows
the readvertisements of files will actually allow someone to connect
to servers and see what is stored there... this violates the
anonymity idea, but it was requested by users, and it can be
easily switched off.

>
>If you could explain the protocol more, it would be appreciated.  We're
>trying to better develop and formalize the notion of anonymity,
>especially in terms of publishing (file-sharing) systems.  A lot of
>systems are starting to claim "anonymity", really without specifying
>exactly what it is (Freenet, Gnutella, Publius, etc.)  I guess this is
>somewhat a concern when users place data in the system, and have
>different assumptions of their protection than what it actually
>offered.  Hopefully, we'll all be able to better develop this notion to
>clear up misunderstandings and work towards stronger cryptographic
>protections.

This is where we differ... if I wanted to try and protect against
the NSA or Israelis I certainly wouldnt be using a 512bit DH Key
exchange or a 128bit homebrew (XTEA based) cipher. Blocks sacrifices
quite a bit in order to deomonstrate ideas but not to burden the
whole system with them. I think Blocks is reasonably secure (or at
least it will be when its finished) in that it will be *very*
expensive for someone to get enough information to prove that
someone published or served particular content... certainly
prohibitively expensive for sys admins or ISPs.

The big question about Blocks is that it is currently unknown
what people will use it for. Perhaps people want a Napster/Gnutella
clone, in which case Blocks is more than secure enough for the
sort of content that tends to be published there. If people really
do want to publish content of a more contraversial content then
for what I can see things like Freehaven may well be more suitable,
and, if Freehaven (or similar) becomes as useable as GNUtella, I
could see Blocks and friends losing popularity very quickly.

Hopefully I'll have docs on the protocol up on the webpage within
a week or two, but its not a high priority right now (and Im not
the best technical author :-)

Freehaven looks quite interesting... I'll have a poke around your
site from time to time (it seems to be down right now tho).

ttfn

PG.



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