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From: "Raystonn ." <raystonn@hotmail.com>
To: "Peter Todd" <pete@petertodd.org>
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In-Reply-To: <20150608214443.GC19826@muck>
Date: Mon, 8 Jun 2015 15:01:34 -0700
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Cc: Bitcoin Dev <bitcoin-development@lists.sourceforge.net>,
	"Patrick Mccorry \(PGR\)" <patrick.mccorry@newcastle.ac.uk>
Subject: Re: [Bitcoin-development] New attack identified and potential
	solution	described: Dropped-transaction spam attack against
	the blocksize limit
Precedence: list

> There will always be a blocksize limit based on technological=20
> considerations - the network has a finite bandwidth limit.

A bandwidth limit is not the same as a blocksize limit.  Bandwidth is uniqu=
e=20
to every individual.  Miners in China have different bandwidth and=20
connectivity than miners in the U.S.=2C for example.  But the block size li=
mit=20
is dictated for eveyone.  They are not comparable.

> Without a blocksize limit the attacker would just flood the network until=
=20
> the bandwidth usage became so great that consensus would fail=2C renderin=
g=20
> Bitcoin both worthless=2C and insecure.

No=2C with no blocksize limit=2C a spammer would would flood the network wi=
th=20
transactions until they ran out of money.  Meanwhile=2C everyone would jump=
 on=20
board trying to mine the blocks to collect the fees from the spammers.  It=
=20
could be one of the greatest transfers of wealth ever.  Bitcoin=20
infrastructure would build up to handle the required bandwidth=2C paid for =
by=20
the very entity spamming the network.  Bitcoin would flourish=2C growing=20
wildly as long as the fees kept coming.  This is antifragility at its best.

> The worst an attacker flooding the network with transactions with a=20
> blocksize limit can do is raise costs=2C without harming security.

No=2C at attacker flooding the network with transactions with a blocksize=20
limit can keep their fees high enough that perhaps 1% of transactions comin=
g=20
from real end-users go through.  At this point everyone would give up on=20
Bitcoin as it would become completely unusable.  The BTCUSD market would=20
tank=2C making it even easier to pay the transaction fees to keep real=20
transactions out of blocks=2C as it would continue to become cheaper and=20
eventually cost-free to obtain the bitcoin fees through market purchase.


-----Original Message-----=20
From: Peter Todd
Sent: Monday=2C June 08=2C 2015 2:44 PM
To: Raystonn .
Cc: Patrick Mccorry (PGR) =3B Bitcoin Dev
Subject: Re: [Bitcoin-development] New attack identified and potential=20
solution described: Dropped-transaction spam attack against the blocksize=20
limit

On Mon=2C Jun 08=2C 2015 at 02:33:54PM -0700=2C Raystonn . wrote:
> > the attack would be expensive.
>
> For attacks being waged to destroy Bitcoin by filling all blocks with spa=
m=20
> transactions=2C the attack succeeds when the attacker is well funded.  Th=
is=20
> gives well-funded private and/or public entities the means to destroy=20
> Bitcoin if they desire.  This is only true after the block size limit was=
=20
> implemented.  Without the block size limit=2C the spam doesn=E2=80=99t ha=
rm Bitcoin.=20
> It simply enriches miners at the cost of the spammers=2C which is a nicel=
y=20
> antifragile quality.

There will always be a blocksize limit based on technological=20
considerations - the network has a finite bandwidth limit.

Without a blocksize limit the attacker would just flood the network until=20
the bandwidth usage became so great that consensus would fail=2C rendering=
=20
Bitcoin both worthless=2C and insecure.

The worst an attacker flooding the network with transactions with a=20
blocksize limit can do is raise costs=2C without harming security. Keep in=
=20
mind=2C that at some point it'd be cheaper to just 51% attack the network.=
=20
Based on the current block subsidy of 25BTC/MB that's at the point where=20
transaction fees are 25mBTC/KB=2C which corresponds to <$2/tx fees - not th=
at=20
cheap=2C but still quite affordable for a large percentage of Bitcoin's use=
rs=20
right now. And that's the *absolute worst-case* attack possible.