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From: Anthony Towns <aj@erisian.com.au>
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Subject: Re: [bitcoin-dev] Adjusted difficulty depending on relative
	blocksize
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On 14 August 2015 at 16:48, Jakob R=C3=B6nnb=C3=A4ck <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> 14 aug 2015 kl. 16:20 skrev Anthony Towns <aj@erisian.com.au>:
>
> On 14 August 2015 at 11:59, Jakob R=C3=B6nnb=C3=A4ck <
> bitcoin-dev@lists.linuxfoundation.org> wrote:
>
>> What if one were to adjust the difficulty (for individual blocks)
>> depending on the relative size to the average block size of the previous
>> difficulty period? (I apologize if i=E2=80=99m not using the correct ter=
ms, I=E2=80=99m not
>> a real programmer, and I=E2=80=99ve only recently started to subscribe t=
o the
>> mailing list)
>>
>
> =E2=80=8BThat would mean that as usage grew, blocksize could increase, bu=
t
> confirmation times would also increase (though presumably less than
> linearly). That seems like a loss?
>
> Would that really be the case though? If it takes 5% to find a block, but
> it contains 5% more transactions would that not mean it=E2=80=99s the sam=
e? That
> would argue against the change if not for the fact that the blocks will b=
e
> bigger for the next difficulty period.
>

=E2=80=8BIf you're waiting for one confirmation, something like that works =
-- you
might from 95% chance of 10 minutes 5% chance of 20 minutes to 100% chance
of 10m30s. But if you want 144 confirmations (eg) you go from 95% chance of
1 day, 5% chance of 1 day 10 minutes; to 100% chance of 1 day 72 minutes.

> If you also let the increase in confirmation time (due to miners finding
> harder blocks rather than a reduction in hashpower) then get reflected ba=
ck
> as decreased difficulty, it'd probably be simpler to just dynamically
> adjust the max blocksize wouldn't it?
>
> I guess that could make the difficulty fluctuate a bit depending on the
> amount of transactions and the fees being paid. Would it really matter in
> the long run though? Since it=E2=80=99s the same amount of miners, doesn=
=E2=80=99t that
> just mean it=E2=80=99s just the number that is lower, not the actual inve=
stment
> needed to mine the blocks? Not sure if this would open up some forms of
> attacks on the system for someone willing to lose money though=E2=80=A6
>

Once blocksizes had normalised as much larger than 1MB with a corresponding
higher average hashrate, a bad actor could easily mine a raft of valid
empty/small blocks at the minimum hash rate and force a reorg (and do
doublespends, etc).

=E2=80=8BCheers,
aj=E2=80=8B

--=20
Anthony Towns <aj@erisian.com.au>

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<div dir=3D"ltr"><div class=3D"gmail_default" style=3D"font-family:monospac=
e"><span style=3D"font-family:arial,sans-serif">On 14 August 2015 at 16:48,=
 Jakob R=C3=B6nnb=C3=A4ck </span><span dir=3D"ltr" style=3D"font-family:ari=
al,sans-serif">&lt;<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org"=
 target=3D"_blank">bitcoin-dev@lists.linuxfoundation.org</a>&gt;</span><spa=
n style=3D"font-family:arial,sans-serif"> wrote:</span></div><div class=3D"=
gmail_extra"><div class=3D"gmail_quote"><blockquote class=3D"gmail_quote" s=
tyle=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div=
><div><div style=3D"word-wrap:break-word"><div><div><blockquote type=3D"cit=
e"><div>14 aug 2015 kl. 16:20 skrev Anthony Towns &lt;<a href=3D"mailto:aj@=
erisian.com.au" target=3D"_blank">aj@erisian.com.au</a>&gt;:</div><br><div>=
<div dir=3D"ltr"><div style=3D"font-family:monospace"><span style=3D"font-f=
amily:arial,sans-serif">On 14 August 2015 at 11:59, Jakob R=C3=B6nnb=C3=A4c=
k=C2=A0</span><span dir=3D"ltr" style=3D"font-family:arial,sans-serif">&lt;=
<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org" target=3D"_blank">=
bitcoin-dev@lists.linuxfoundation.org</a>&gt;</span><span style=3D"font-fam=
ily:arial,sans-serif">=C2=A0wrote:</span><br></div><div class=3D"gmail_extr=
a"><div class=3D"gmail_quote"><blockquote class=3D"gmail_quote" style=3D"ma=
rgin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,=
204);border-left-style:solid;padding-left:1ex">What if one were to adjust t=
he difficulty (for individual blocks) depending on the relative size to the=
 average block size of the previous difficulty period? (I apologize if i=E2=
=80=99m not using the correct terms, I=E2=80=99m not a real programmer, and=
 I=E2=80=99ve only recently started to subscribe to the mailing list)<br></=
blockquote><div><br></div><div><div style=3D"font-family:monospace">=E2=80=
=8BThat would mean that as usage grew, blocksize could increase, but confir=
mation times would also increase (though presumably less than linearly). Th=
at seems like a loss?</div></div></div></div></div></div></blockquote>Would=
 that really be the case though? If it takes 5% to find a block, but it con=
tains 5% more transactions would that not mean it=E2=80=99s the same? That =
would argue against the change if not for the fact that the blocks will be =
bigger for the next difficulty period.</div></div></div></div></div></block=
quote><div><br></div><div><div class=3D"gmail_default" style=3D"font-family=
:monospace">=E2=80=8BIf you&#39;re waiting for one confirmation, something =
like that works -- you might from 95% chance of 10 minutes 5% chance of 20 =
minutes to 100% chance of 10m30s. But if you want 144 confirmations (eg) yo=
u go from 95% chance of 1 day, 5% chance of 1 day 10 minutes; to 100% chanc=
e of 1 day 72 minutes.<span style=3D"font-family:arial,sans-serif">=C2=A0</=
span></div></div><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8=
ex;border-left:1px #ccc solid;padding-left:1ex"><div><div><div style=3D"wor=
d-wrap:break-word"><div><div><blockquote type=3D"cite"><div dir=3D"ltr"><di=
v class=3D"gmail_extra"><div class=3D"gmail_quote"><div><div style=3D"font-=
family:monospace">If you also let the increase in confirmation time (due to=
 miners finding harder blocks rather than a reduction in hashpower) then ge=
t reflected back as decreased difficulty, it&#39;d probably be simpler to j=
ust dynamically adjust the max blocksize wouldn&#39;t it?</div></div></div>=
</div></div></blockquote></div><div>I guess that could make the difficulty =
fluctuate a bit depending on the amount of transactions and the fees being =
paid. Would it really matter in the long run though? Since it=E2=80=99s the=
 same amount of miners, doesn=E2=80=99t that just mean it=E2=80=99s just th=
e number that is lower, not the actual investment needed to mine the blocks=
? Not sure if this would open up some forms of attacks on the system for so=
meone willing to lose money though=E2=80=A6</div></div></div></div></div></=
blockquote><div><br></div><div><div class=3D"gmail_default" style=3D"font-f=
amily:monospace">Once blocksizes had normalised as much larger than 1MB wit=
h a corresponding higher average hashrate, a bad actor could easily mine a =
raft of valid empty/small blocks at the minimum hash rate and force a reorg=
 (and do doublespends, etc).</div><br></div><div><div class=3D"gmail_defaul=
t" style=3D"font-family:monospace">=E2=80=8BCheers,</div><div class=3D"gmai=
l_default" style=3D"font-family:monospace">aj=E2=80=8B</div></div></div><di=
v><br></div>-- <br><div>Anthony Towns &lt;<a href=3D"mailto:aj@erisian.com.=
au" target=3D"_blank">aj@erisian.com.au</a>&gt;</div>
</div></div>

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