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In-Reply-To: <201608040327.36571.luke@dashjr.org>
References: <CAAEDBiGMGWLeC81vkojGwEqQTT1HQaE=a3z114u6=FXXM2DRtQ@mail.gmail.com>
	<201608040327.36571.luke@dashjr.org>
From: Andrew Johnson <andrew.johnson83@gmail.com>
Date: Wed, 3 Aug 2016 23:49:26 -0400
Message-ID: <CAAy62_JGZ0srYK4DKb5DOb5hz2OjvS6wXtnAnoAj9+KvEGTsDg@mail.gmail.com>
To: Luke Dashjr <luke@dashjr.org>,
	Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>
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Subject: Re: [bitcoin-dev] BIP clearing house addresses
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"This is already possible. Just nLockTime your withdrawls for some future
block. Don't sign any transaction that isn't nLockTime'd at least N blocks
beyond the present tip."

This would have prevented the Bitfinex hack if BitGo did this, but it
wouldn't have helped if the Bitfinex offline key had been compromised
instead of BitGo doing the 2nd sig.  In the BFX hack the TXNs were signed
by Bitfinex's hot key and BitGo's key, they required 2 of 2.

If I'm understanding correctly, what Matthew is proposing is a new type of
UTXO that is only valid to be spent as an nLockTime transaction and can be
reversed by some sort of RBF-type transaction within that time period, I
believe.

But I don't think this will work. What do you do if the keys are
compromised?  What's to stop the attacker from locking the coins up
indefinitely by repeatedly broadcasting a refund transaction each time you
try to spend to an uncompromised address?

You'd need a third distinct key required for the refund TXN that's separate
from the keys used to sign the initial nLockTime TXN.  And the refund TXN
would need to be able to go to a new address entirely.

On Aug 3, 2016 11:28 PM, "Luke Dashjr via bitcoin-dev" <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> On Wednesday, August 03, 2016 6:16:20 PM Matthew Roberts via bitcoin-dev
> wrote:
> > In light of the recent hack: what does everyone think of the idea of
> > creating a new address type that has a reversal key and settlement layer
> > that can be used to revoke transactions?
>
> This isn't something that makes sense at the address, since it represents
> the
> recipient and not the sender. Transactions are not sent from addresses
> ever.
>
> > You could specify so that transactions "sent" from these addresses must
> > receive N confirmations before they can't be revoked, after which the
> > transaction is "settled" and the coins become redeemable from their
> > destination output. A settlement phase would also mean that a
> transaction's
> > progress was publicly visible so transparent fraud prevention and
> auditing
> > would become possible by anyone.
>
> This is already possible. Just nLockTime your withdrawls for some future
> block. Don't sign any transaction that isn't nLockTime'd at least N blocks
> beyond the present tip.
>
> Luke
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>

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<p dir=3D"ltr">&quot;This is already possible. Just nLockTime your withdraw=
ls for some future<br>
block. Don&#39;t sign any transaction that isn&#39;t nLockTime&#39;d at lea=
st N blocks<br>
beyond the present tip.&quot;</p>
<p dir=3D"ltr">This would have prevented the Bitfinex hack if BitGo did thi=
s, but it wouldn&#39;t have helped if the Bitfinex offline key had been com=
promised instead of BitGo doing the 2nd sig.=C2=A0 In the BFX hack the TXNs=
 were signed by Bitfinex&#39;s hot key and BitGo&#39;s key, they required 2=
 of 2.</p>
<p dir=3D"ltr">If I&#39;m understanding correctly, what Matthew is proposin=
g is a new type of UTXO that is only valid to be spent as an nLockTime tran=
saction and can be reversed by some sort of RBF-type transaction within tha=
t time period, I believe.</p>
<p dir=3D"ltr">But I don&#39;t think this will work. What do you do if the =
keys are compromised?=C2=A0 What&#39;s to stop the attacker from locking th=
e coins up indefinitely by repeatedly broadcasting a refund transaction eac=
h time you try to spend to an uncompromised address?</p>
<p dir=3D"ltr">You&#39;d need a third distinct key required for the refund =
TXN that&#39;s separate from the keys used to sign the initial nLockTime TX=
N.=C2=A0 And the refund TXN would need to be able to go to a new address en=
tirely.</p>
<div class=3D"gmail_extra"><br><div class=3D"gmail_quote">On Aug 3, 2016 11=
:28 PM, &quot;Luke Dashjr via bitcoin-dev&quot; &lt;<a href=3D"mailto:bitco=
in-dev@lists.linuxfoundation.org">bitcoin-dev@lists.linuxfoundation.org</a>=
&gt; wrote:<br type=3D"attribution"><blockquote class=3D"gmail_quote" style=
=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">On Wedne=
sday, August 03, 2016 6:16:20 PM Matthew Roberts via bitcoin-dev<br>
wrote:<br>
&gt; In light of the recent hack: what does everyone think of the idea of<b=
r>
&gt; creating a new address type that has a reversal key and settlement lay=
er<br>
&gt; that can be used to revoke transactions?<br>
<br>
This isn&#39;t something that makes sense at the address, since it represen=
ts the<br>
recipient and not the sender. Transactions are not sent from addresses ever=
.<br>
<br>
&gt; You could specify so that transactions &quot;sent&quot; from these add=
resses must<br>
&gt; receive N confirmations before they can&#39;t be revoked, after which =
the<br>
&gt; transaction is &quot;settled&quot; and the coins become redeemable fro=
m their<br>
&gt; destination output. A settlement phase would also mean that a transact=
ion&#39;s<br>
&gt; progress was publicly visible so transparent fraud prevention and audi=
ting<br>
&gt; would become possible by anyone.<br>
<br>
This is already possible. Just nLockTime your withdrawls for some future<br=
>
block. Don&#39;t sign any transaction that isn&#39;t nLockTime&#39;d at lea=
st N blocks<br>
beyond the present tip.<br>
<br>
Luke<br>
_______________________________________________<br>
bitcoin-dev mailing list<br>
<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org">bitcoin-dev@lists.=
linuxfoundation.org</a><br>
<a href=3D"https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev" =
rel=3D"noreferrer" target=3D"_blank">https://lists.linuxfoundation.org/mail=
man/listinfo/bitcoin-dev</a><br>
</blockquote></div></div>

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