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From: Karl <gmkarl@gmail.com>
Date: Sun, 16 May 2021 14:10:12 -0400
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To: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
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Subject: Re: [bitcoin-dev] Proposal: Force to do nothing for first 9 minutes
 to save 90% of mining energy
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[sorry if I haven't replied to the other thread on this, I get swamped
by email and don't catch them all]

This solution is workable but it seems somewhat difficult to me at this tim=
e.

The clock might be implementable on a peer network level by requiring
inclusion of a transaction that was broadcast after a 9 minute delay.

Usually a 50% hashrate attack is needed to reverse a transaction in
bitcoin.  With this change, this naively appears to become a 5%
hashrate attack, unless a second source of truth around time and order
is added, to verify proposed histories with.

A 5% hashrate attack is much harder here, because the users of mining
pools would be mining only 10% of the time, so compromising mining
pools would not be as useful.

Historically, hashrate has increased exponentially.  This means that
the difficulty of performing an attack, whether it is 5% or 50%, is
still culturally infeasible because it is a multiplicative, rather
than an exponential, change.

If this approach were to be implemented, it could be important to
consider how many block confirmations people wait for to trust their
transaction is on the chain.  A lone powerful miner could
intentionally fork the chain more easily by a factor of 10.  They
would need to have hashrate that competes with a major pool to do so.

> How would you prevent miners to already compute the simpler difficulty pr=
oblem directly after the block was found and publish their solution directl=
y after minute 9? We would always have many people with a finished / compet=
ing solution.

Such a chain would have to wait a longer time to add further blocks
and would permanently be shorter.

> Your proposal won=E2=80=99t save any energy because it does nothing to de=
crease the budget available to mine a block (being the block reward).

You are assuming this budget is directly related to energy
expenditure, but if energy is only expended for 10% of the same
duration, this money must now be spent on hardware.  The supply of
bitcoin hardware is limited.

In the long term, it won't be, so a 10% decrease is a stop-gap
measure.  Additionally, in the long term, we will have quantum
computers and AI-designed cryptography algorithms, so things will be
different in a lot of other ways too.