Re: [bitcoin-dev] Defending against empty or near empty blocks from malicious miner takeover?

From: "Emin Gün Sirer" <el33th4x0r@gmail•com>
To: Bitcoin Dev <bitcoin-dev@lists•linuxfoundation.org>,
	 CANNON <cannon@cannon-ciota•info>
Subject: Re: [bitcoin-dev] Defending against empty or near empty blocks from malicious miner takeover?
Date: Fri, 24 Mar 2017 09:27:47 -0700	[thread overview]
Message-ID: <CAPkFh0s-ZyLN06h+EpU2rfgs5TkTEPG+3FZyWSXusp-Z9XHasQ@mail.gmail.com> (raw)
In-Reply-To: <5b9ba6c4-6d8f-9c0b-2420-2be6c30f87b5@cannon-ciota.info>

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Because there's no consensus on the contents of the mempool, this approach
is unsafe and will lead to forks. It also opens a new attack vector where
people can time the flood of new transactions with the discovery of a block
by a competitor, to orphan the block and to fork the chain.

The technical defense against an attacking majority of miners is to change
the PoW, effectively moving the community off into a new altcoin where the
attackers, hopefully, don't have majority hash power.

- egs

Sent from my phone, please compensate for autocorrect errors.

On Mar 24, 2017 9:06 AM, "CANNON via bitcoin-dev" <
bitcoin-dev@lists•linuxfoundation.org> wrote:

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> When the original white paper was written the idea was that nodes
> would be miners at same time. That the distribution of mining power
> being mostly on par with the distribution of nodes if I understand
> correctly. The problem we face now I fear, is the mining power
> becoming centralized. Even if every bitcoin node invested a $1000
> into mining power and mined at a loss, it still would not even
> make a dent in hash distribution. Currently there are around 6000
> known nodes. If each node invested $1000 for say 10 ths of hashing
> power. At current hashrate of around 3,674,473,142 GH/s this would
> only make up %16 of hash power. This is out of balance as while
> nodes are distributed mining power is becoming very centralized
> due to the creation of monopolization of ASICs. The problem we
> are facing is a small group of a couple people whom control a
> large amount and growing of hash power. At time of this writing
> it has quickly risen to 39% and at current rate will soon become
> 50% of hashing power that is controlled by a small group of a few
> people. Their intentions are too hijack the bitcoin network to a
> cryptocurrency that suits their dangerous agenda. Dangerous because
> their plan would centralize power of consensus as I understand it,
> to themselves the miners. Dangerous also because the code base of
> the attempting subverters is buggy, insecure, and reckless from a
> technological standpoint. Even though they only have very minute
> amount of nodes compared to legitimate bitcion nodes, the danger
> is that they are very quickly taking over in mining power. While
> it is true that nodes will not accept invalid blocks that would be
> attempted to be pushed by the conspirators, they are threatening to
> attack the valid (or in their words, "minority chain") by dedicating
> some mining power soley to attacking the valid chain by mining empty
> blocks and orphaning the valid chain. So even though the majority
> of nodes would be enforcing what blocks are valid and as a result
> block the non-compliant longer chain, the conspiring miner can simply
> (as they are currently threatening to) make the valid chain unuseable
> by mining empty blocks.
>
> If a malicious miner with half or majority control passes invalid
> blocks, the worst case scenario is a hardfork coin split in which
> the non-compliant chain becomes an alt. However the problem is that
> this malicious miner is very recently threatening to not just simply
> fork, but to kill the valid chain to force economic activity to the
> adversary controlled chain. If we can simply defend against attacks
> to the valid chain, we can prevent the valid chain from dying.
>
> While empty or near empty blocks would generally be protected by
> the incentive of miners to make money. The threat is there if the
> malicious miner with majority control is willing to lose out on
> these transaction fees and block reward if their intention is to
> suppress it to force the majority onto their chain.
>
> Proposal for potential solution Update nodes to ignore empty blocks,
> so this way mined empty blocks cannot be used to DOS attack the
> blockchain. But what about defense from say, blocks that are
> not empty but intentionally only have a couple transactions
> in it? Possible to have nodes not only ignore empty blocks,
> but also blocks that are abnormally small compared to number of
> valid transactions in mempool?
>
> For example would be something like this:
> If block = (empty OR  <%75 of mempool) THEN discard
> This threshold just an example.
>
> What would be any potentials risks
> and attacks resulting from both having such new rulesets and not
> doing anything?
>
> Lets assume that the first problem of blocking empty or near empty
> blocks has been mitigated with the above proposed solution. How
> likely and possible would it be for a malicious miner with lots of
> mining power to orphan the chain after so many blocks even with
> non empty blocks? Is there a need to mitigate this?
> If so is it possible?
>
> Time is running short I fear. There needs to be discussion on various
> attacks and how they can be guarded against along with various
> other contingency plans.
>
> - --
> Cannon
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> Email: cannon@cannon-ciota•info
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