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

Aymeric Vitte vitteaymeric at gmail.com
Fri Mar 24 19:00:40 UTC 2017


Since I have been working on crypto currencies/bitcoin, I kept
repeating: btc should make a priority to significantly increase the
ridiculous number of full nodes we have today, design an incentive for
people to run full nodes and design a system for people to setup full
nodes in an acceptable timeframe

Unfortunately, this was not a priority at all, maybe because of some
historical consensus between miners and devs, so here we are today, some
miners became crazy, the situation would be much more different if more
full nodes were there

Because, how comes everybody perfectly knows the plans of the conspiring
miners? They were stupid enough to explain very precisely how they will
perform the attack?

If I were them I would in addition setup quite a lot of nodes (which
probably they are planning to do, because anyway they need them for the
new sw), not difficult, not so expensive

Defending against abnormal blocks looks to be a non issue, I suppose
that the btc devs perfectly know how to create a pattern based on
history to detect abnormal blocks (including some strange transactions)
and reject them, but this further depends on the ability of current full
nodes to upgrade, which apparently is not what they do the best

I don't know what "Time is running short I fear" stands for and when 50%
is supposed to be reached

Given that it looks difficult to quickly increase the number of full
nodes, that increasing the mining power by standard means looks too
expensive, useless and not profitable, that a counter attack based on a
new proof of something does not look to be ready, then maybe the btc
folks should ask Bram Cohen (who by some luck is participating to this
list) to resurrect the bitcoin miner Epic Scale which Bittorrent Inc (in
an umpteenth dubious attempt to make money) tried some time ago to
include quietly in utorrent forgetting to ask the authorization of the
selected users, then utorrent users might upgrade (potentially 150 M),
and the resulting mining power might be sufficient, depending on the
incentive for this, which is TBD

Or activate by anticipation proof of space... unlike bitcoin-qt,
utorrent sw is quite good to be intrusive, run in background when you
think you have closed it, run things you don't know, etc, so quite
efficient in this situation

Then if btc folks wants to promote full nodes too, it would not be a bad
idea to put the bitcoin-qt blockchain + chain state in a torrent making
sure it is seeded correctly (there are plenty of academics here, they
can do it and run full nodes too) so people can download it and setup
full nodes (incentive TBD too) assuming they know about upnp/port forwarding


Le 24/03/2017 à 17:03, CANNON via bitcoin-dev a écrit :
> 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.
>
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