Subject: Re: [bitcoin-dev] Drivechain proposal using OP_COUNT_ACKS

From: Sergio Demian Lerner <[email-masked]>
Date: Sun, 2 Oct 2016 19:36:29 -0300

On Sun, Oct 2, 2016 at 6:46 PM, Russell O'Connor via bitcoin-dev <
[email-masked]> 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.