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From: Sergio Demian Lerner <sergio.d.lerner@gmail.com>
Date: Mon, 8 May 2017 19:15:48 -0300
Message-ID: <CAKzdR-qFXqPdRczxeQtmJVwBRx2QLNK1acAD1q1miLJthipsSA@mail.gmail.com>
To: Natanael <natanael.l@gmail.com>
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Cc: Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>,
	Eric Lombrozo <eric@ciphrex.com>
Subject: Re: [bitcoin-dev] Full node "tip" function
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Yes you practically can. No proxy can defeat the protocol investing less
money than buying storage space to store the blockchain.

Even with challenge-response delays of minutes.  That's why it will be
fully controlled by a RSK smart-contract, with no user intervention.
I'm will post about this soon.


On Mon, May 8, 2017 at 6:44 PM, Natanael <natanael.l@gmail.com> wrote:

>
> Den 8 maj 2017 23:01 skrev "Sergio Demian Lerner via bitcoin-dev" <
> bitcoin-dev@lists.linuxfoundation.org>:
>
> I'll soon present a solution to encourage full nodes to store the
> blockchain based on Proof-of-Unique-Blockchain-Storage (PoUBS)
>
>
> Proving that you're holding your own copy of the blockchain, not shared
> with other nodes? I don't think that's possible to do securely. It falls on
> that the whole blockchain is both public and static, while any such proof
> of independence needs to rely on unique capabilities per node.
>
> All you can do with a challenge-response protocol is to prevent honest
> nodes from being unwitting backends to dishonest transparent proxy nodes
> (by binding the challenge to cryptographic node identities).
>
> Even latency bounding protocols can't stop you from putting multiple
> *seemingly independent* nodes in front of the same backend with one single
> copy of the blockchain.
>
> I believe best you can do is to force somebody to hold multiple copies
> locally on multiple hardware units to not run out of memory I/O when
> creating proofs for multiple remote nodes, through using memory heavy
> functions for the proof of storage, forcing quick random access. However
> somebody willing to put enough RAM in a server rack to hold the full
> blockchain could still easily pretend to be multiple regular nodes with
> independent copies.
>
> Any kind of attempt at forcing the full copy of the blockchain to be in
> memory close to the CPU will either rule out most nodes from passing or
> will be cheatable.
>

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<div dir=3D"ltr">Yes you practically can. No proxy can defeat the protocol =
investing less money than buying storage space to store the blockchain.<div=
><br><div>Even with challenge-response delays of minutes.=C2=A0 That&#39;s =
why it will be fully controlled by a RSK smart-contract, with no user inter=
vention.</div><div>I&#39;m will post about this soon.<div><br></div><div><b=
r></div><div><br></div></div></div></div><div class=3D"gmail_extra"><br><di=
v class=3D"gmail_quote">On Mon, May 8, 2017 at 6:44 PM, Natanael <span dir=
=3D"ltr">&lt;<a href=3D"mailto:natanael.l@gmail.com" target=3D"_blank">nata=
nael.l@gmail.com</a>&gt;</span> wrote:<br><blockquote class=3D"gmail_quote"=
 style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><d=
iv dir=3D"auto"><span class=3D""><div class=3D"gmail_extra" dir=3D"auto"><b=
r><div class=3D"gmail_quote">Den 8 maj 2017 23:01 skrev &quot;Sergio Demian=
 Lerner via bitcoin-dev&quot; &lt;<a href=3D"mailto:bitcoin-dev@lists.linux=
foundation.org" target=3D"_blank">bitcoin-dev@lists.<wbr>linuxfoundation.or=
g</a>&gt;:<br type=3D"attribution"><blockquote class=3D"m_67384626744989422=
30quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left=
:1ex"><div dir=3D"ltr"><div><div>I&#39;ll soon present a solution to encour=
age full nodes to store the blockchain based on Proof-of-Unique-Blockchain-=
Sto<wbr>rage (PoUBS)</div></div></div></blockquote></div></div><div dir=3D"=
auto"><br></div></span><div dir=3D"auto">Proving that you&#39;re holding yo=
ur own copy of the blockchain, not shared with other nodes? I don&#39;t thi=
nk that&#39;s possible to do securely. It falls on that the whole blockchai=
n is both public and static, while any such proof of independence needs to =
rely on unique capabilities per node.=C2=A0</div><div dir=3D"auto"><br></di=
v><div dir=3D"auto">All you can do with a challenge-response protocol is to=
 prevent honest nodes from being unwitting backends to dishonest transparen=
t proxy nodes (by binding the challenge to cryptographic node identities).=
=C2=A0</div><div dir=3D"auto"><br></div><div dir=3D"auto">Even latency boun=
ding protocols can&#39;t stop you from putting multiple *seemingly independ=
ent* nodes in front of the same backend with one single copy of the blockch=
ain.=C2=A0</div><div dir=3D"auto"><br></div><div dir=3D"auto">I believe bes=
t you can do is to force somebody to hold multiple copies locally on multip=
le hardware units to not run out of memory I/O when creating proofs for mul=
tiple remote nodes, through using memory heavy functions for the proof of s=
torage, forcing quick random access. However somebody willing to put enough=
 RAM in a server rack to hold the full blockchain could still easily preten=
d to be multiple regular nodes with independent copies.=C2=A0</div><div dir=
=3D"auto"><br></div><div dir=3D"auto">Any kind of attempt at forcing the fu=
ll copy of the blockchain to be in memory close to the CPU will either rule=
 out most nodes from passing or will be cheatable.=C2=A0</div><div class=3D=
"gmail_extra" dir=3D"auto"></div></div>
</blockquote></div><br></div>

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