Subject: Re: [bitcoin-dev] Selfish Mining Prevention

From: Moral Agent <[email-masked]>
Date: Fri, 14 Sep 2018 10:49:16 -0400

You might be interested in an idea I wrote about that is in a similar
spirit here:

https://medium.com/coinmonks/taming-large-miners-with-helper-blocks-6ae67ac242f6

>From the article:

When a block is solved, it randomly selects one satoshi from the utxo set
and gives whomever controls that satoshi the power to generate a “Helper
Block”. The Helper Block commits to a subset of transactions for inclusion
in the next block. A miner can accept the Helper Block by including the
suggested transactions and giving the associated transaction fees to a
payment address specified in the Helper Block. Miners who do not use a
Helper Block must satisfy a 25% higher difficulty.

On Fri, Sep 14, 2018 at 9:56 AM Andrew via bitcoin-dev <
[email-masked]> wrote:

> I discussed this more at bitcointalk:
> https://bitcointalk.org/index.php?topic=4998410.0
>
> The attacks I'm interested in preventing are not only selfish mining
> and collusion, but also more subtle attacks like block withholding,
> and in general anything that aims to drive out the competition in
> order to increase hashrate fraction. I also scrapped the idea of
> changing the block subsidies, and I am only focuses on fees.
>
> You can read more about the motivation and details in the bitcointalk
> thread, but my proposal in short would be to add the concept of
> "reserve fees". When a user makes a transaction, for each txout
> script, they can add parameters that specify the fraction of the total
> fee that is held in "reserve" and the time it is held in "reserve"
> (can set a limit of 2016 blocks). This "reserve" part of the fee will
> be paid to miners if the hashrate rises. So if hashrate is currently h
> and peak hashrate (from past year) is p, then for each period (1 day),
> a new hashrate is calculated h1, and if h1 > h, then the fraction
> (h1-h)/p from the reserve fees created in the past 2016 blocks will be
> released to miners for that period (spread out over the 144 blocks in
> that period). And this will keep happening as long as hashrate keeps
> rising, until the "contract" expires, and the leftover part can be
> used by the owner of the unspent output, but it can only be used for
> paying fees, not as inputs for future transactions (to save on block
> space).
>
> This should incentivize miners to not drive out the competition, since
> if they do, there will be less of these reserve fees given to miners.
> Yes in the end the miners will get all the fees, but with rising
> hashrate they get an unconditional subsidy that does not require
> transactions, thus more space for transactions with fees.
>
> I can make a formal BIP and pull request, but I need to know if there
> is interest in this. Now fees don't play such a large part of the
> block reward, but they will get more important, and this change
> wouldn't force anything (would be voluntary by each user), just miners
> have to agree to it with a soft fork (so they don't spend from the
> anyone-can-spend outputs used for reserve fees). Resource requirements
> for validation are quite small I believe.
>
> On Sat, Sep 1, 2018 at 12:11 AM, Andrew <[email-masked]> wrote:
> > As I understand, selfish mining is an attack where miners collude to
> > mine at a lower hashrate then with all miners working independently.
> > What are the current strategies used to prevent this and what are the
> > future plans?
> >
> > One idea I have is to let the block reward get "modulated" according
> > to peak hashrate. Say p is the peak hashrate for 365 periods (1 year)
> > consisting of 144 blocks, h is the hashrate of the last 144 block (1
> > day) period, and r is the base subsidy (12.5 BTC currently). You can
> > then make the max block reward 0.5 r (1 + h/p). So if hashrate is at
> > peak you get the full reward. Otherwise you get less, down to a min of
> > 0.5 r.
> >
> > If miners were to collude to mine at a lower than peak hashrate, then
> > they may be able to do it profitably for 144 blocks, but after that,
> > the reward would get modulated and it wouldn't be so much in their
> > interest to continue mining at the lower hashrate.
> >
> > What flaws are there with this? I know it could be controversial due
> > to easier mining present for early miners, so maybe it would have to
> > be done in combination with a new more dynamic difficulty adjustment
> > algorithm. But I don't see how hashrate can continue rising
> > indefinitely, so a solution should be made for selfish mining.
> >
> > Also when subsidies stop and a fee market is needed, I guess a portion
> > of the fees can be withheld for later if hashrate is not at peak.
> >
> >
> > --
> > PGP: B6AC 822C 451D 6304 6A28  49E9 7DB7 011C D53B 5647
>
>
>
> --
> PGP: B6AC 822C 451D 6304 6A28  49E9 7DB7 011C D53B 5647
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