From: Isidor Zeuner <cryptocurrencies@quidecco.de>
To: odinn <odinn.cyberguerrilla@riseup.net>
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References: <54760A50.201@riseup.net>
	<CAJHLa0N6+hpwNECpHUSiKuj4-BYohh=Wr1DP=67Ff8xVBsi8-Q@mail.gmail.com>
In-Reply-To: <54760A50.201@riseup.net>
Message-Id: <20141127020947.A13D2E19A09@quidecco.de>
Date: Thu, 27 Nov 2014 03:09:47 +0100 (CET)
Cc: Bitcoin Development <bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] Deanonymisation of clients in Bitcoin P2P
 network paper
Precedence: list

Hello there,

quote:
> Please see also the following:
>
> https://cpunks.org//pipermail/cypherpunks/2014-November/005971.html
>

I agree about the severity of the Tor/Bitcoin issue, but I see no
point in bashing Bitcoin's financial privacy characteristics as
the linked pages seem to do.

Bitcoin can be useful as a part of a strategy to improve on privacy,
but it does not intend to be a run-and-forget solution for doing so.

A lot of issues found in this context can actually be traced back to
Tor's characteristics already known before. It's just that
Bitcoin makes Tor's deficiencies more measurable - before Bitcoin,
those interested in researching how Tor performs in an automated
context where a much smaller community. In the end, I guess both
projects can benefit from the research we can do now.

> Respect,
>
> - -Odinn
>
> Jeff Garzik:
> > I don't recall being contacted directly, but the attack has been
> > discussed.  It relies on a number of conditions.  For example, if
> > you are over Tor, they try to kick the machine off Tor, _assuming_
> > that it will fall back to non-Tor.  That's only true for dual stack
> > nodes, which are not really 100% anonymous anyway -- you're
> > operating from your public IP anyway.
> >

Generally, it cannot be said that the attack vector described here is
irrelevant for non-dual-stack nodes. An attacker might not be able to
collect IP addresses of Tor-only nodes, but he can try to kick the
users from all Tor exit nodes he does not control, and proceed with
other attacks when a large number of Tor-only users connect through
his Tor exit node(s).

Since this attack vector has been discussed, I started making some
measurements on how effective it is to connect to Bitcoin using Tor,
and I found that the number of connections dropping to near-zero is
a situation which occurs rather frequently, which suggests that there
is still room to improve on the DoS handling.

Best regards,

Isidor