[bitcoin-dev] Managing block size the same way we do difficulty (aka Block75)

James MacWhyte macwhyte at gmail.com
Sun Dec 18 21:53:57 UTC 2016

Hi All,

I'm coming late to the party. I like the Block75 proposal.

Multiple people have said miners would/could stuff blocks with insincere
transactions to increase the block size, but it was never adequately
explained what they would gain from this. If there aren't enough legitimate
transactions to fill up the block, where do you plan to earn extra income
once the block is bigger?

Miners would be incentivized to include as many legitimate transactions as
possible, but if propagation time is as big an issue as some of you have
said it is, miners would also be incentivized to keep their blocks small
enough to propagate. So why not give them the choice? Once the block size
gets too big to propagate effectively, miners would be naturally
incentivized to limit how much data they put in each block, finding the
perfect balance.

In my opinion, none of the downsides presented so far have been a good
argument. Risk of a 51% attack is not unique to this proposal, saying "we
could also do that with hardcoded limits" doesn't actually point out any
problem with this proposal, and miners already have the ability to add or
withhold transactions from their blocks.

We trust our miners to serve us by acting in their own best interests, and
this proposal simply gives them more options for doing that. If anyone can
make a strong argument against that would earn top marks in a high school
debate class, I'd love to hear it!


On Sun, Dec 11, 2016 at 3:23 PM s7r via bitcoin-dev <
bitcoin-dev at lists.linuxfoundation.org> wrote:

> Andrew Johnson wrote:
> > "You miss something obvious that makes this attack actually free of cost.
> > Nothing will "cost them more in transaction fees". A miner can create
> > thousands of transactions paying to himself, and not broadcast them to
> > the network, but hold them and include them in the blocks he mines. The
> > fees are collected by him because transactions are included in a block
> > that he mined and the left amount is in another wallet of the same
> > person. Repeat this continuously to fill blocks."
> >
> > This is easily detectable as long as the network isn't heavily
> > partitioned(which is an assumption we make today in order for
> > transaction propagation to work reliably as well as for xThin and
> > CompactBlocks to work effectively to reduce block transmission time).
> > Other miners would have an incentive to intentionally orphan blocks that
> > contained a large number of transactions that their nodes were unaware
> of.
> >
> > I don't think this sort of attack would last long.  Even later when
> > subsidies are drastically reduced, you would still lose out on
> > significant genuine fee revenue if your orphan rate increased even
> > 10%(one out of ten of your poison blocks intentionally orphaned by
> > another miner).
> >
> I disagree.
> I didn't say this is impossible to detect, but it is hard to act against
> it. One miner orphaning the block intentionally is very unlikely if that
> miner acts rationally. It would only make sense if 51% of the hash rate
> would intentionally orphan it. Otherwise the miner who intentionally
> orphans a valid block, let's say block X, has to continue to mine one in
> its place on top of block X-1, and by the time he finds one:
> a) his block X' is rejected by other miners because they already have a
> valid block X on top of which they already started to mine;
> b) block X+1 was already found and broadcasted, so the miner who
> orphaned X intentionally is on the shorter chain ignored by the network.
> So, one miner cannot do anything about it. Even a pool cannot do
> anything about it, because the loss is greater. You need 51% of the hash
> rate to intentionally orphan it, and all the miners forming 51% need to
> be colluding and know for sure that every one will intentionally orphan
> the said block, otherwise there's a huge risk of loss for who does it.
> Nobody would gamble to do this (I am not sure if gambling is the right
> word, since the loss is 100% sure here). But, we are not discussing 51%
> attacks because those are a different topic.
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