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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
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> the only way a transaction can be removed from a Bitcoin Core mempool is
> through it getting mined, double-spent, or the node restarting.
Right. And that results in some transactions with insufficient fees getting
dropped today after many hours.
> The protection that we have against that attack is that you need access to
> a lot of bitcoins to pay enough fees.
That's no protection against a well-funded private and/or public entity.
Without the block size limit, this attack doesn't exist. It would simply
result in a transfer of wealth from spammer to miners, which is a nicely
antifragile response for the Bitcoin network.
-----Original Message-----
From: Peter Todd
Sent: Monday, June 08, 2015 2:33 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
> > there is no memory pool cap currently
>
> Real hardware does not have an infinite amount of RAM. Memory pool sizes
> cannot grow unbounded. Some transactions with insufficient fees do get
> dropped today after many hours.
Actually they don't, which is an unfortunate problem with the existing
mempool implementation; the only way a transaction can be removed from a
Bitcoin Core mempool is through it getting mined, double-spent, or the
node restarting.
The protection that we have against that attack is that you need access
to a lot of bitcoins to pay enough fees. With the 0.01mBTC/KB minimum
relay fee and $230 USD/BTC that works out to about $2.3kUSD/GB of ram
consumed, and furthermore, actually getting that many transactions to
propagate over the network is non-trivial. (no, I'm not going to tell
you how)
The obvious solution is to cap the size of the mempool and evict
transactions lowest fee/KB first, but if you do that they you (further)
break zeroconf security. On the other hand, if you don't break zeroconf
security an attacker can prevent reasonable fee transactions from
propagating.
I probably should get around to fixing this...
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