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From: Sergio Demian Lerner <sergio.d.lerner@gmail.com>
Date: Sun, 2 Oct 2016 19:36:29 -0300
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To: "Russell O'Connor" <roconnor@blockstream.io>, 
	Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Content-Type: multipart/alternative; boundary=94eb2c06652ecaacaa053de977c7
Subject: Re: [bitcoin-dev] Drivechain proposal using OP_COUNT_ACKS
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On Sun, Oct 2, 2016 at 6:46 PM, Russell O'Connor via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

>
> But I would argue that in this scenario, the only way it
>> would become invalid is the equivalent of a double-spend... and therefore
>> it
>> may be acceptable in relation to this argument.
>>
>
> The values returned by OP_COUNT_ACKS vary in their exact value depending
> on which block this transaction ends up in.  While the proposed use of this
> operation is somewhat less objectionable (although still objectionable to
> me), nothing stops users from using OP_EQUALVERIFY and and causing their
> transaction fluctuate between acceptable and unacceptable, with no party
> doing anything like a double spend.  This is a major problem with the
> proposal.
>

Transactions that redeem an output containing (or referencing by means of
P2WSH) an OP_COUNT_ACKS are not broadcast by the network. That means that
the network cannot be DoS attacked by flooding with a transaction that will
not verify due to being too late.
The only parties that can include the redeem transaction are the miners
themselves.
Therefore I see no problem that an OP_COUNT_ACKS scriptSig transaction is
invalidated after the liveness times expires.
If there is no expiration, then polls can last forever and the system fails
to provide DoS protection for block validation since active polls can
accumulate forever.

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<div dir=3D"ltr"><br><div class=3D"gmail_extra"><br><div class=3D"gmail_quo=
te">On Sun, Oct 2, 2016 at 6:46 PM, Russell O&#39;Connor via bitcoin-dev <s=
pan dir=3D"ltr">&lt;<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org=
" target=3D"_blank">bitcoin-dev@lists.linuxfoundation.org</a>&gt;</span> wr=
ote:<br><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border=
-left:1px #ccc solid;padding-left:1ex"><div dir=3D"ltr"><br><div class=3D"g=
mail_extra"><div class=3D"gmail_quote"><span class=3D""><blockquote style=
=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding=
-left:1ex" class=3D"gmail_quote">But I would argue that in this scenario, t=
he only way it<br>
would become invalid is the equivalent of a double-spend... and therefore i=
t<br>
may be acceptable in relation to this argument.<br></blockquote><div><br></=
div></span><div>The values returned by <span class=3D"m_-780418529899519097=
7gmail-im">OP_COUNT_ACKS vary in their exact value depending on which block=
 this transaction ends up in.=C2=A0 While the proposed use of this operatio=
n is somewhat less objectionable (although still objectionable to me), noth=
ing stops users from using OP_EQUALVERIFY and and causing their transaction=
 fluctuate between acceptable and unacceptable, with no party doing anythin=
g like a double spend.=C2=A0 This is a major problem with the proposal.<br>=
</span></div></div></div></div></blockquote><div><br></div><div>Transaction=
s that redeem an output containing (or referencing by means of P2WSH) an OP=
_COUNT_ACKS are not broadcast by the network. That means that the network c=
annot be DoS attacked by flooding with a transaction that will not verify d=
ue to being too late.<br></div><div>The only parties that can include the r=
edeem transaction are the miners themselves.<br></div><div>Therefore I see =
no problem that an OP_COUNT_ACKS scriptSig transaction is invalidated after=
 the liveness times expires.<br></div><div>If there is no expiration, then =
polls can last forever and the system fails to provide DoS protection for b=
lock validation since active polls can accumulate forever. <br><br><br></di=
v><div><br></div></div></div></div>

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