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Date: Wed, 26 Feb 2025 14:11:51 -0500
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Subject: Re: [bitcoindev] Update on the Great Consensus Cleanup Revival
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On 2/23/25 5:35 PM, Antoine Poinsot wrote:
>     A 40x decrease to a validation time of 30 seconds probably is worth a=
 bit of risk for a further
>     improvement.
>=20
>=20
> Depends on what hardware. I don't think a worst case of 30 seconds for en=
d users is worth more=20
> risks. A worst case of 30 seconds for miners would probably be concerning=
.

Sure, I'm not super concerned with an RPi. I am concerned with relatively c=
heap miner hardware, tho.

> In addition, although the worst case is important to limit the damage an =
attacker can do without=20
> being economically rational, what we care about for miners attacking each=
 other is economically=20
> viable attacks. At the moment the optimal "validation time / cost to atta=
cker" ratio is not the=20
> worst case, by a large margin [0].
>=20
> I believe we should take into account the worst case to miners even if no=
t economically viable for=20
> an attacker as a safety margin. But we should keep in mind this is alread=
y overestimating the attack=20
> risk since in this scenario what we should look at is the worst case vali=
dation time of blocks that=20
> may have positive returns to an attacker.

Fair enough.

>     Can you put numbers to this?
>=20
>=20
> Sure. Using my functional test which runs the worst case today and the wo=
rst case under various=20
> mitigations [1] on a Dell XPS 15 9520 laptop (the model with an i5-12500H=
) i get 120 seconds for the=20
> worst case today and 10 seconds for the worst block with a limited of 250=
0 (potentially) executed=20
> sigops per transaction. To (maybe, they could be running more powerful ma=
chines than my laptop)=20
> impose such a validation time to other miners an attacker would have to i=
nvest 89 (!!) preparation=20
> blocks. Sure, with low fees the opportunity cost of mining preparation tr=
ansactions is not as high=20
> as it could be. But still.

Okay! That's a much better outcome than I was thinking. I assume this was w=
ith parallelization=20
across the 4+8 available cores? Do you happen to have numbers handy for the=
 worst-case with, for=20
example, one block of prep?

Matt

> [0] https://delvingbitcoin.org/t/worst-block-validation-time-inquiry/711/=
70 <https://=20
> delvingbitcoin.org/t/worst-block-validation-time-inquiry/711/70?u=3Dantoi=
nep>
> [1] https://delvingbitcoin.org/t/worst-block-validation-time-inquiry/711/=
61 <https://=20
> delvingbitcoin.org/t/worst-block-validation-time-inquiry/711/61?u=3Dantoi=
nep>
> On Thursday, February 20th, 2025 at 8:22 PM, Matt Corallo <lf-lists@mattc=
orallo.com> wrote:
>> In the delving post you said =E2=80=9CThis provides a 40x decrease in th=
e worst case validation time with=20
>> a straightforward and flexible rule minimizing the confiscatory surface.=
 A further 7x decrease is=20
>> possible by combining it with another rule, which is in my opinion not w=
orth the additional=20
>> confiscatory surface.=E2=80=9D
>>
>> Can you put numbers to this? How long does it take to validate a full bl=
ock with this 40x decrease=20
>> and how long would it take with the further 7x decrease?
>>
>> A 40x decrease to a validation time of 30 seconds probably is worth a bi=
t of risk for a further=20
>> improvement. A 40x decrease to 1 second is obviously fine :).
>>
>>> On Feb 5, 2025, at 19:57, 'Antoine Poinsot' via Bitcoin Development Mai=
ling List=20
>>> <bitcoindev@googlegroups.com> wrote:
>>>
>>> =EF=BB=BFHi everyone,
>>>
>>> A bit over a year ago i started working on revisiting the 2019 Great Co=
nsensus Cleanup proposal from
>>> Matt Corallo [0]. His proposal included:
>>> - making <=3D64 bytes transactions invalid to fix merkle tree weaknesse=
s;
>>> - making non-pushonly scriptSigs, FindAndDelete matches, OP_CODESEPARAT=
OR and non-standard sighash
>>> =C2=A0types fail script validation to mitigate the worst case block val=
idation time;
>>> - restrict the nTime field of the first block in each difficulty adjust=
ment interval to be no less
>>> =C2=A0than 600 seconds lower than the previous block's;
>>>
>>> I set out to research the impact of each of the vulnerabilities this in=
tended to patch, the
>>> alternative fixes possible for each and finally if there was any other =
protocol bug fix we'd want to
>>> include if we went through the considerable effort of soft forking Bitc=
oin already.
>>>
>>> Later in March i shared some first findings on Delving [1] and advertiz=
ed the effort on this mailing
>>> list [2]. I also created a companion thread on Delving, kept private, t=
o discuss the details of the
>>> worst case block validation time [3]. As one would expect due to the la=
rger design space available
>>> to fix this issue, this private thread is where most of the discussion =
would happen. Thank you to
>>> everyone who contributed feedback, insights, ideas and argumented opini=
ons on the different issues
>>> all along the process.
>>>
>>> Now i would like to update the broader Bitcoin development community on=
 the outcome of this effort.
>>> I believe a Consensus Cleanup proposal should include the following.
>>> - A fix for vulnerabilities surrounding the use of timestamps in the di=
fficulty adjustment
>>> =C2=A0algorithm. =C2=A0In particular, a fix for the timewarp attack wit=
h a 7200 seconds grace period as well
>>> =C2=A0as a fix for the Murch-Zawy attack [4] by making invalid any diff=
iculty adjustment period with a
>>> =C2=A0negative duration.
>>> - A fix for long block validation times with a minimal "confiscation su=
rface", by introducing a
>>> =C2=A0per-transaction limit on the number of legacy sigops in the input=
s.
>>> - A fix for merkle tree weaknesses by making transactions which seriali=
ze to exactly 64 bytes
>>> =C2=A0invalid.
>>> - A fix for duplicate transactions to supplement BIP34 in order to avoi=
d resuming unnecessary BIP30
>>> =C2=A0validation in the future. This is achieved by mandating the nLock=
Time field of coinbase
>>> =C2=A0transaction to be set to the height of their block minus 1.
>>>
>>> I have started drafting a BIP draft with the detailed specs for this.
>>>
>>> Antoine Poinsot
>>>
>>>
>>> [0] https://github.com/TheBlueMatt/bips/blob/7f9670b643b7c943a0cc6d2197=
d3eabe661050c2/bip-=20
>>> XXXX.mediawiki
>>> [1] https://delvingbitcoin.org/t/great-consensus-cleanup-revival/710
>>> [2] https://groups.google.com/g/bitcoindev/c/CAfm7D5ppjo/m/bYJ3BiOuAAAJ
>>> [3] https://delvingbitcoin.org/t/worst-block-validation-time-inquiry/71=
1
>>> [4] https://delvingbitcoin.org/t/zawy-s-alternating-timestamp-attack/10=
62#variant-on-zawys-attack-2
>>>
>>> --=20
>>> You received this message because you are subscribed to the Google Grou=
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>>> To unsubscribe from this group and stop receiving emails from it, send =
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>=20

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