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Date: Mon, 6 May 2013 11:25:50 -0700
Message-ID: <CAAS2fgSh+dYxSak8HvE0Sr4=zxzRc=3dMQ6X_nD_a+OdacUBZQ@mail.gmail.com>
From: Gregory Maxwell <gmaxwell@gmail.com>
To: Adam Back <adam@cypherspace.org>
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Cc: Bitcoin Dev <bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] Discovery/addr packets (was: Service bits
 for pruned nodes)
Precedence: list

On Mon, May 6, 2013 at 11:04 AM, Adam Back <adam@cypherspace.org> wrote:
> bitcoins primary
> vulnerability IMO (so far) is network attacks to induce network splits,
> local lower difficulty to a point that a local and artificially isolated
> area of the network can be fooled into accepting an orphan branch as the
> one-true block chain,

Uh.  It currently costs about 2016*25*$120 =3D six million dollars to
reduce the difficulty in your isolated fork by a factor of 4.

To reduce it by a factor of 1000 (what would be required to make a
parallel fork that you could maintain in realtime with a single avalon
device) the cost is  sum(2016*25/4^n*120,n,0,ceil(log4(1000))) or
about eight million dollars.

Surely you can think of attacks on Bitcoin which are less expensive
than eight million dollars. :P

> maybe even from node first install time.

Protecting against that=E2=80=94 making sure any such attack has to start f=
rom
a high difficulty=E2=80=94 is, in my opinion, the biggest continued
justification for checkpoints.

> (btw I notice most of the binaries and tar balls are not signed, nor serv=
ed
> from SSL - at least for linux).

They are signed.

> With ToR, it has a similar bootstrap problem to bitcoin.  So while that m=
ay
> help it is also passing the buck, not necessarily solving the problem.  A=
nd

No, it doesn't. It has centrally controlled directories that publish
an official Truth of the Network. Someone can isolate you and thus DOS
you, but they can't put you on a fantasy tor network.  But ...
centeralized.

> as I said I think its possible bitcoin has a higher assurance need in tha=
t
> the attackers motivated my $$ might put more effort in than the odd

It does, and we also consider decentralization a core value. But even
the tor project would like to decentralize more.