Subject: Re: [Bitcoin-development] New attack identified and potential solution described: Dropped-transaction spam attack against the blocksize limit

From: "Raystonn ." <[email-masked]>
Date: Mon, 8 Jun 2015 15:01:34 -0700

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

A bandwidth limit is not the same as a blocksize limit.  Bandwidth is unique 
to every individual.  Miners in China have different bandwidth and 
connectivity than miners in the U.S., for example.  But the block size limit 
is dictated for eveyone.  They are not comparable.

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

No, with no blocksize limit, a spammer would would flood the network with 
transactions until they ran out of money.  Meanwhile, everyone would jump on 
board trying to mine the blocks to collect the fees from the spammers.  It 
could be one of the greatest transfers of wealth ever.  Bitcoin 
infrastructure would build up to handle the required bandwidth, paid for by 
the very entity spamming the network.  Bitcoin would flourish, growing 
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 
> blocksize limit can do is raise costs, without harming security.

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

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

On Mon, Jun 08, 2015 at 02:33:54PM -0700, Raystonn . wrote:
> > the attack would be expensive.
>
> For attacks being waged to destroy Bitcoin by filling all blocks with spam 
> transactions, the attack succeeds when the attacker is well funded.  This 
> gives well-funded private and/or public entities the means to destroy 
> Bitcoin if they desire.  This is only true after the block size limit was 
> implemented.  Without the block size limit, the spam doesn’t harm Bitcoin. 
> It simply enriches miners at the cost of the spammers, which is a nicely 
> antifragile quality.

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

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

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