From: CANNON <cannon@cannon-ciota.info>
Message-ID: <5b9ba6c4-6d8f-9c0b-2420-2be6c30f87b5@cannon-ciota.info>
Date: Fri, 24 Mar 2017 16:03:31 +0000
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Subject: [bitcoin-dev] Defending against empty or near empty blocks from
 malicious miner takeover?
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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
PGP Fingerprint: 2BB5 15CD 66E7 4E28 45DC 6494 A5A2 2879 3F06 E832 
Email: cannon@cannon-ciota.info

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