Re: [bitcoin-dev] Does Bitcoin require or have an honest majority or a rational one? (re rbf)

[Jeremy Rubin <jeremy.l.rubin@gmail.com>]

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Building on the most work chain is perhaps not rational in many normal
circumstances that can come up today under the stated reference strategy:

1) Take highest paying transactions that fit
2) Mine on tips

E.g., suppose:

Block N: Fees = 10, reward = 1

Mempool: Fees = 2

Mining block N+1 with the mempool leads to reward 2+1 = 3, reorging leads
to reward of up to 10 + 1 + c, (c < 2, where c is the extra transactions
that fit). Assume instead your reward is 8, leaving 3+c on the table.

If you assume all other miners are tip miners, and there are two
conflicting tips, they should pick the one with the more profit for them,
which is the new one you made as a non-tip miner since you "shared" some
fee.

You aren't particularly more likely to remine block N or N+1, before
someone builds on it, as opposed to deeper reorgs (which require larger
incentive).


However, as many have pointed out, perhaps not following the simple "honest
tip mining" strategy is bad for bitcoin, so maybe we should expect it not
to happen often? Or other strategies to emerge around selecting
transactions so that the next M blocks have a similar fee profile, as
opposed to picking greedily for the next block.


--
@JeremyRubin <https://twitter.com/JeremyRubin>


On Sun, Oct 16, 2022 at 3:03 PM <email@yancy.lol> wrote:

> The proof-of-work also solves the problem of determining
> representation in majority decision
> making. If the majority were based on one-IP-address-one-vote, it
> could be subverted by anyone
> able to allocate many IPs. Proof-of-work is essentially
> one-CPU-one-vote. The majority
> decision is represented by the longest chain, which has the greatest
> proof-of-work effort invested
> in it. If a majority of CPU power is controlled by honest nodes, the
> honest chain will grow the
> fastest and outpace any competing chains. To modify a past block, an
> attacker would have to
> redo the proof-of-work of the block and all blocks after it and then
> catch up with and surpass the
> work of the honest nodes. We will show later that the probability of a
> slower attacker catching up
> diminishes exponentially as subsequent blocks are added.
>
>
> It's interesting that Nash Equilibrium isn't mentioned here.  Since each
> miner has the option to either contribute to the longest chain or not, even
> if the miners know what strategy the other miners will use, they still
> wouldn't change their decision to contribute to the majority.
>
>
> For example, if I run a shop that takes rain checks, but I sell an
> item to a higher bidder who didn't have a hold on the item, that is
> not honest, but it may be selfish profit maximizing.
>
>
> It would be honest if the store policy said ahead of time they are allowed
> to sell rain checks for more in such an occurrence.  Although this is a
> good example of the difference between honest and rational.  I think this
> means it's not a Nash Equilibrium if we needed to rely on the store owner
> to be honest.
>
>
> Satoshi said an honest majority is required for the chain to be
> extended. Honest is not really defined though. Honesty, in my
> definition, is that you follow a pre specified rule, rational or not.
>
>
> My take is that "rational" is probably a better word than honest.  In
> terms of a Nash Equilibrium, each participant is simply trying to maximize
> their outcome and honesty doesn't matter (only that participants are
> rational).
>
>
> It seems a lot of the RBF controversy is that Protocol developers have
> aspired to make the honest behavior also be the rational behavior.
> This is maybe a good idea because, in theory, if the honest behavior
> is rational then we can make a weaker assumption of selfishness
> maximizing a parameter.
>
>
> I'm curious, can RBF can be described by a Nash Equilibrium?  If yes, then
> it also shouldn't matter if participants are honest?
>
>
> Overall, it might be nice to more tightly document what bitcoins
> assumptions are in practice and what those assumptions do in terms of
> properties of Bitcoin, as well as pathways to weakening the
> assumptions without compromising the behaviors users expect the
> network to have.  An "extended white paper" if you will.
>
>
> White paper 1.1 :D
>
>
> A last reflection is that Bitcoin is specified with an honest majority
> assumption, but also has a rational dishonest minority assumption over
> both endogenous (rewards) and exogenous (electricity) costs. Satoshi
> did not suggest, at least as I read it, that Bitcoin works with an
> rational majority assumption. (If anyone thinks these three are
> similar properties you can make some trivial counterexamples)
>
>
> My take is the opposite unless I'm missing something.  Participants are
> always incentivized to choose the rational solution (Not to waste
> electricity on a minority chain).
>
> Cheers,
> -Yancy
>
> On 2022-10-16 19:35, Jeremy Rubin via bitcoin-dev wrote:
>
> The Bitcoin white paper says:
>
> The proof-of-work also solves the problem of determining
> representation in majority decision
> making. If the majority were based on one-IP-address-one-vote, it
> could be subverted by anyone
> able to allocate many IPs. Proof-of-work is essentially
> one-CPU-one-vote. The majority
> decision is represented by the longest chain, which has the greatest
> proof-of-work effort invested
> in it. If a majority of CPU power is controlled by honest nodes, the
> honest chain will grow the
> fastest and outpace any competing chains. To modify a past block, an
> attacker would have to
> redo the proof-of-work of the block and all blocks after it and then
> catch up with and surpass the
> work of the honest nodes. We will show later that the probability of a
> slower attacker catching up
> diminishes exponentially as subsequent blocks are added.
>
> This, Satoshi (who doesn't really matter anyways I guess?) claimed
> that for Bitcoin to function properly you need a majority honest
> nodes.
>
> There are multiple behaviors one can describe as honest, and
> economically rational or optimizing is not necessarily rational.
>
> For example, if I run a shop that takes rain checks, but I sell an
> item to a higher bidder who didn't have a hold on the item, that is
> not honest, but it may be selfish profit maximizing.
>
> Satoshi said an honest majority is required for the chain to be
> extended. Honest is not really defined though. Honesty, in my
> definition, is that you follow a pre specified rule, rational or not.
>
> It seems a lot of the RBF controversy is that Protocol developers have
> aspired to make the honest behavior also be the rational behavior.
> This is maybe a good idea because, in theory, if the honest behavior
> is rational then we can make a weaker assumption of selfishness
> maximizing a parameter.
>
> However, Satoshi did not particularly bound what aspects of honesty
> are important for the network, because there isn't a spec defining
> exactly what is honest or not. And also as soon as people are honest,
> you can rely on that assumption for good effect.
>
> And sometimes, defining an honest behavior can be creating a higher
> utility system because most people are "law abiding citizens" who
> might not be short term rational. For example, one might expect that
> miners would be interested in making sure lightning closes are
> "accurate" because increasing the utility of lightning is good for
> Bitcoin, even if it is irrational.
>
> It seems that the NoRBF crowd want to rely on an honest majority
> assumption where the honest behavior is not doing replacement if not
> requested. This is really not much different than trying to close
> lightning channels "the right way".
>
> However, where it may be different, is that even in the presence of
> honest majority, the safety of 0conf isn't assured given the potential
> of race conditions in the mempool. Therefore it's not clear to me that
> 0conf working well is something you can drive from the Honest Majority
> Assumption (where honest includes first seen).
>
> Overall, it might be nice to more tightly document what bitcoins
> assumptions are in practice and what those assumptions do in terms of
> properties of Bitcoin, as well as pathways to weakening the
> assumptions without compromising the behaviors users expect the
> network to have.  An "extended white paper" if you will.
>
>  It's somewhat clear to me that we shouldn't weaken assumptions that
> only seem local to one subsystem of Bitcoin if they end up
> destabilizing another system. In particular, things that decrease
> "transaction utility" for end users decrease the demand for
> transactions which hurts the fee market's longer term viability, even
> if we feel good about making an honest policy assumption into a self
> interested policy assumption.
>
> A last reflection is that Bitcoin is specified with an honest majority
> assumption, but also has a rational dishonest minority assumption over
> both endogenous (rewards) and exogenous (electricity) costs. Satoshi
> did not suggest, at least as I read it, that Bitcoin works with an
> rational majority assumption. (If anyone thinks these three are
> similar properties you can make some trivial counterexamples)
>
> Cheers,
>
> Jeremy
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> bitcoin-dev@lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>
>

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